belajar Astronomy

Supermoon 19 Maret 2011

2011-03-20T00:27:00.008+07:00

Karena fenomena Supermoon ini cukup heboh dan banyak menimbulkan salah persepsi, mari coba dibahas sedikit meskipun sebenarnya fenomena ini bukanlah fenomena astronomi yang penting. Impact atau efeknya hampir tidak ada selain tinggi air pasang air laut sedikit lebih tinggi.

The Moon looks extra-big when it is beaming through foreground objects--a.k.a. "the Moon illusion." Credit: NASA

Dari perhitungan astronomi, pada tanggal 19 Maret 2011 Bulan dalam peredarannya mengelilingi Bumi, akan berada pada posisi paling dekat dengan Bumi, disebut sebagai posisi perigee. Tentunya dalam peredaran mengitari Bumi, Bulan akan selalui melalui posisi perigee, tetapi posisi perigee tersebut tidak selalu berada pada angka yang tepat sama, tetapi bervariasi sepanjang waktu.

Pada tanggal tersebut, yang pada saat itu Bulan dalam fase Purnama, dalam perhitungan merupakan jarak yang paling dekat ke Bumi semenjak 18 tahun yang lalu. Lalu? Apa yang akan terjadi? Beredar kabar di dunia maya, bahwa pada saat tersebut, akan terjadi bencana alam yang sangat dahsyat, mulai dari badai besar, gempa Bumi sampai dengan letusan gunung berapi. Sepertinya seram sekali! Tetapi benarkah itu?

Mari kita tinjau satu persatu, pertama, fenomena ‘supermoon’, ini sebetulnya adalah fenomena alam yang biasa terjadi. Pada suatu ketika, dalam peredarannya di langit, Bulan-Bumi-Matahari bisa berada dalam satu garis lurus, biasanya pada saat itu bisa terjadi bulan baru atau bulan purnama. Dan bila pada saat bulan purnama, Bulan berada pada posisi perigee, maka keadaan ini oleh para ahli astrologi (bukan ahli astronomi!) disebut ‘super moon’! Jadi istilah super moon bukanlah istilah astronomi, tetapi istilah astrologi.

Kedua, pada tanggal itu, akan terjadi bencana alam? Tentulah dalam siklus alamiah, Bulan mempengaruhi terjadinya gaya pasang surut laut di Bumi, dan ketika Bulan ‘mendekat’, tentulah pengaruh gravitasi Bulan menjadi lebih besar (demikian yang dikatakan hukum gravitasi Newton). Akan tetapi, apakah bila pengaruh gravitasi Bulan menjadi lebih besar, akan terjadi bencana alam? Mari kita sedikit berhitung dengan matematika. Ambil rata-rata jarak Bumi-Bulan 382900 km, sedangkan pada tanggal 19 Maret 2011, Bumi-Bulan berjarak 356577 km, atau ‘mendekat’ sejarak 26323 km, atau hanya 6,87% lebih dekat dibanding rata-rata.

Posisi Bulan saat berada di perigee atau titik terdekat dengan Bumi. courtsey physcorg.com

Dengan jarak yang sekecil itu (6,87%), akan menyebabkan dampak yang luar biasa? Seperti biasa, efek pasang surut terjadi setiap hari, dan bila resultan vektor gaya gravitasi Bulan & Matahari menjadi lebih besar maka efek pasang surut menjadi lebih besar. Menurut physorg.com (yang mengutip NASA), efek "perigeean ides" ini hanya menambah tinggi air pasang beberapa cm saja (maximum 15 cm).

Posisi Bumi-Bulan-Matahari dan kaitannya dengan pasang surut. kredit : Boomeria.org

Tentunya pada saat ketika purnama ditambah perigee, gaya gravitasi menjadi lebih berpengaruh, tetapi, dari studi geofisika yang telah banyak dilakukan, tidak dtemukan adanya dampak yang signifikan pada keseimbangan energi Bumi. Gempa Bumi, letusan vulkanik, ataupun berbagai fenomena di Bumi lebih disebabkan keseimbangan energi di Bumi, seperti pergeseran lempeng Bumi, sedangkan efek pasang surut oleh Bulan, tidaklah cukup kuat menggeser keseimbangan energi tersebut, yang artinya ‘super moon’ tidak akan menyebabkan bencana alam.

Mungkin dibutuhkan seorang Superman yang datang dari planet Kripton untuk menggeser keseimbangan Bumi, karena Superman mempunyai kekuatan yang jauh lebih besar dibanding kekuatan super moon; tetapi kita tahu bahwa superman adalah tokoh rekaan, sebagaimana bencana akibat super moon adalah telaah astrologi. Kalau sudah demikian, pertanyaan berikut, apa yang akan terjadi di tanggal 19 Maret yang akan datang?

Yang pasti Bulan akan tampak lebih ‘besar’ 14% dan 30% lebih cerlang di Banding ‘biasanya’, namun bisakah Anda membedakannya (bukan karena Anda punya asumsi awal bahwa Bulan lebih besar dari biasanya)?

Bulan Purnama saat di perigee akan tampak lebih besar 14%. kredit: NASA

Jawabannya belum tentu. Di langit tidak ada penggaris/meteran yang dapat digunakan untuk mengukur diameter Bulan (selain Anda menggunakan teleskop dengan skala ukuran di lensa nya). Jika Anda mengamati Bulan saat di titik tertingginya dan tidak ada benda lain sebagai pembanding, maka Anda tidak dapat membedakan bulan purnama ini (super moon) dengan bulan purnama biasa.

Untuk mendapatkan efek "piringan Bulan yang besar", Anda disarankan mengamati Bulan saat ada di dekat horizon. Pada posisi ini, ada efek ilusi optik yang akan menciptakan kesan bahwa piringan Bulan nampak lebih besar dari biasanya (efek ini terjadi pada saat gerhana Bulan "biasa" juga). Alasannya masih sulit dijelaskan oleh astronomer maupun psikolog. Bulan yang dekat dengan horizon akan nampak "sangat" besar (lihat ilustrasi gambar pertama).

So, apakah fenomena supermoon penting untuk diamati? jawabnya tergantung Anda. Anda bisa memanfaatkan momentum ini untuk mengadakan observasi Bulan bersama teman Anda, baik dengan mengamati langsung maupun dengan binokular/teleskop kecil.

Artikel di atas disadur dari Langit Selatan dengan beberapa perubahan yang diambil dari physorg.com.

Documentaries

2011-03-07T02:35:00.005+07:00

Beberapa kumpulan documentary yang menarik untuk disimak.

1. Universe: The Cosmology Quest

2. The Search for Life: The Drake Equation

3. The Universe
link

4. How the Universe Works

5. The Birth Of Earth
Part 1

Part 2

Part 3

Semoga bermanfaat

Pseudoscience vs Science

2011-02-09T06:49:00.003+07:00

Akhir - akhir ini banyak sekali berita di media massa yang nampak seperti science namun sebenarnya hanya pseudo-science. Berikut ini ada artikel yang bagus mengenai hal ini, yang dikutip dari www.astronomynotes.com. Selamat membaca dan semoga bermanfaat.

"Yes, the world would be a more interesting place if there were UFOs lurking in the deep waters off Bermuda and eating ships and planes, or if dead people could take control of our hands and write us messages. It would be fascinating if adolescents were able to make telephone handsets rocket off their cradles just be thinking at them, or if our dreams could, more often than can be explained by chance and our knowledge of the world, accurately foretell the future." Just one nice passage among many, many in Carl Sagan's "The Demon-Haunted World" (available in the campus library and most public libraries). Well, Dr. Sagan, if the world would be more interesting if the unexplained UFOs were in fact space aliens, if we could communicate with the dead or space aliens, etc., why are you scientists such stuffy, party-poopers, insisting that the evidence is not good enough to prove that these things exist? With thousands of eye-witnesses, what more do you need? Sagan wrote that passage above just before he discussed pseudoscience in "The Demon-Haunted World". If we understand the difference between real science and pseudoscience, perhaps we can understand the view of many scientists and skeptics that the UFO research is pseudoscience.

"Pseudo" means "not genuine; sham", something pretending to be something else that it is not. Pseudosciences "purport to use the methods and findings of science, while in fact they are faithless to its nature—often because they are based on insufficient evidence or because they ignore clues that point the other way" (Sagan, 1996). We are awash in pseudoscience from all around us because "pseudoscience is easier to contrive than science" ("contrive" is a pretty strong word choice by Dr. Sagan). With pseudoscience, the standards of argument and what is allowable as evidence are much more relaxed than what you find in science.

This is not to say that all of science is correct. No, there have been plenty of mistakes in science, plenty of blind alleys. No, reality is messier, more unpredictable than the best detective/murder-mystery novel. With science, hypotheses are framed in a way that they can be tested by experiment and observation. Nature has the final veto power in whatever explanation we come up with but scientists are human (yes, they are) and subject to emotional attachments to their explanations. They too can be offended when their pet explanation doesn't pan out, when Nature has vetoed it.

Pseudoscience is just the opposite. Hypotheses are often framed in a way that makes them untestable. "Practitioners [of pseudoscience] are defensive and wary. Skeptical scrutiny is opposed. When the pseudoscientific hypothesis fails to catch fire with scientists, conspiracies to suppress it are deduced" (Sagan, 1996). Ah, yes! How many times have we heard that the science journals won't publish the UFO research with charges of bias and close-mindedness on the part of the science "establishment"? Such charges are part of the conspiracy mindset. I'm sorry, but it is not a conspiracy. It is because the UFO evidence is not of the caliber needed to base conclusions upon and less fantastic alternative explanations that don't involve space aliens are not addressed or explored by the author of the proposed paper. Not every truly scientific paper makes it into the journals either but the scientist doesn't complain of a conspiracy. No, the paper was probably rejected because more data needed to be gathered to improve the signal (the confidence level) above the ever-present statistical fluctuations of reality in order to deduce the conclusion reached by the author. Sometimes, too strong a conclusion is deduced from too weak a data set. Another likelihood is that the author did not explore an alternative explanation because they failed to see the assumptions that they were operating under. Our filters can blind us to the obvious.

"Perhaps the sharpest distinction between science and pseudoscience is that science has a far keener appreciation of human imperfections and fallibility than does pseudoscience." (Sagan, 1996) This is why conclusions based solely (or even mostly) on eye-witness testimony are not acceptable in science, however harsh that may seem to the layman. The Innocence Project (see www.innocenceproject.org) has shown that eyewitness identification has played a significant role in 75% of the convictions that were later overturned through DNA testing. Thirty years of social science research has proven that eyewitness identification is often unreliable. Even victims of horrendous personal crimes have mis-identified the perpetrators. Unfortunately, our memories are malleable. Initial uncertainties in recollection become strongly-held beliefs, bed-rock certainties, once we've had time to try to make sense of what happened. Our creativity can sometimes lead us astray. It can happen to the best of us. Even scientists. Please see Christopher Chabris' and Daniel Simons' Invisible Gorilla website for some of this research and especially see Dan Simons' "Counter-Intuition" talk he gave in April 2010. There is a video of his short talk in the video section of Invisible Gorilla in which he gives powerful examples of our perceptions, intuitions, and even the reasoning about our intuition leading even the best of observers astray. That is why scientists lay their results open to the very critical scrutiny of others. And they agree to accept the criticism and re-submit their work when they have improved their argument through better data or give it up when the observations show that their idea does not have merit. They don't blame the "establishment".

So, it is not because scientists just don't want to believe in space aliens that they are critical of the claims of UFOs as aliens, it is because time and time again the methodology of the UFO claims have not followed the high standards of verifiable scientific research. Has every claim of UFOs-as-space aliens been investigated? No. There are so many! It takes more time and energy to figure out the ordinary, natural cause of something than it takes for creative people to imagine fantastic things. Perhaps scientists are a bit too quick to discount UFOs-as-space aliens claims but after years of going down that dead end interpretation of noisy data, can you understand why they might want to devote their time to something more provable?

The next several pages are lengthy excerpts of Sagan's "The Demon-Haunted World: Science as a Candle in the Dark", published by Ballantine Books (New York) in 1996 (ISBN 0-345-40946-9). These excerpts are examples of alternative, plausible explanations that "point the other way" from that of space aliens and government cover-ups of space alien invasions.

Roswell, New Mexico

What follows is an excerpt from Sagan's "The Demon-Haunted World" about the alleged flying saucer crash in Roswell, NM in 1947 (page 84-86).

A great to-do has been made of one or more alleged crashed flying saucers near Roswell, New Mexico, in 1947. Some initial reports and newspaper photographs of the incident are entirely consistent with the idea that the debris was a crashed high-altitude balloon. But other residents of the region—especially decades later—remember more exotic materials, enigmatic hieroglyphics, threats by military personnel to witnesses if they didn't keep what they knew to themselves, and the canonical story that alien machinery and body parts were packed into an airplane and flown to the Air Materiel Command at Wright-Patterson Air force Base. Some, but not all, of the recovered alien body stories are associated with this incident.

Philip Class, a long-time and dedicated UFO skeptic, has uncovered a subsequently declassified letter dated July 27, 1948, a year after the Roswell" incident," from Major General C.B. Cabell—then Director of Intelligence for the U.S. Air Force (and later, as a CIA offical, a major figure in the abortive U.S. invasion of Cuba at the Bay of Pigs). Cabell was inquiring of those who reported to him on what UFOs might be. He hadn't a clue. In an October 11, 1948 summary response, explicitly including information in the possession of the Air Materiel Command, we find the Director of Intelligence being told that nobody else in the Air Force had a clue either. This makes it unlikely that UFO fragments and occupants had made their way to Wright-Patterson the year before.

What the Air Force was mostly worried about was that UFOs were Russian. Why Russians would be testing flying saucers over the United States was a puzzle to which the following four answers were proposed: "(1) To negate U.S. confidence in the atom bomb as the most advanced and decisive weapon in warfare. (2) To perform photographic reconnaissance missions. (3) To test U.S. air defenses. (4) To conduct familiarization flights [for strategic bombers] over U.S. territory." We now know that UFOs neither were or are Russian, and however dedicated the Soviet interest may have been to objectives (1) through (4), flying saucers weren't how they pursued these objectives.

Much of the evidence regarding the Roswell "incident" seems to point to a cluster of high-altitude classified balloons, perhaps launched from nearby Alamogordo Army Air Field or White Sands Proving Ground, that crashed near Roswell, the debris of secret instruments hurriedly collected by earnest military personnel, early press reports announcing that it was a spaceship from another planet ("RAAF Captures Flying Saucer on Ranch in Roswell Region"), diverse recollections simmering over the years, and memories refreshed by the opportunity for a little fame and fortune. (Two UFO museums in Roswell are leading tourist stops.)
A 1994 report ordered by the Secretary of the Air Force and the Department of Defense in response to prodding from a New Mexico Congressman identifies the Roswell debris as remnants of a long-range, highly secret, balloon-borne low-frequency acoustic detection system call "Project Mogul"—an attempt to sense Soviet nuclear weapons explosions at tropopause altitudes. The Air Force investigators, rummaging comprehensively through the secret files of 1947, found no evidence of heightened message traffic:

There were no indications and warnings, notice of alerts, or a higher tempo of operational activity reported that would be logically generated if an alien craft, whose intentions were unknown, entered U.S. territory…The records indicated that none of this happened (or if it did, it was controlled by a security system so efficient and tight that no one, U.S. or otherwise, has been able to duplicate it since. If such a system had been in effect at the time, it would have also been used to protect our atomic secrets from the Soviets, which history has shown obviously was not the case.)

The radar targets carried by the balloons were partly manufactured by novelty and toy companies in New York, whose inventory of decorative icons seems to have been remembered many years later as alien hieroglyphics.

In an earlier passage Sagan notes that balloons were extensively used by the Air Force in the 1950s for various uses including robotic espionage craft, with high-resolution cameras and signal intelligence devices. "High-altitude balloons can seem saucer-shaped when seen from the ground. If you misestimate how far away they are, you can easily imagine them going absurdly fast. Occasionally, propelled by a gust of wind, they make abrupt changes in direction, uncharacteristic of aircraft and in seeming defiance of the conservation of momentum—if you don't realize that they're hollow and weigh almost nothing." (p. 83) Please remember this when you read about reports of alien craft capable of accelerations and sudden changes of trajectory that are impossible with modern aircraft and would create fatal g-forces for humans.

Spoofing

Another excerpt from Sagan's "The Demon-Haunted World" that gives a plausible explanation of the unknown radar events during the Cold War that were kept under wraps (p. 86-87):

Consider spoofing. In the strategic confrontation between the United states and the Soviet Union, the adequacy of air defenses was a vital issue. It was item (3) on General Cabell's list. If you could find a weakness, it might be the key to "victory" in an all-out nuclear war. The only sure way to test your adversary's defenses is to fly an aircraft over their borders and see how long it takes for them to notice. The United States did this routinely to test Soviet air defenses.

In the 1950s and ‘60s, the United States had state-of-the-art radar defense systems covering its west and east coats, and especially its northern approaches (over which a Soviet bomber or missile attack would most likely come). But there was a soft underbelly—no significant early warning system to detect the geographically much more taxing southern approach. This is of course information vital for a potential adversary. It immediately suggests a spoof: One or more of the adversary's high-performance aircraft zoom out of the Caribbean, let's say, into U.S. airspace, penetrating, let's say, a few hundred miles up the Mississippi River until a U.S. air defense radar locks on. Then the intruders hightail it out of there. (Or, as a control experiment, a unit of U.S. high-performance aircraft is sequestered and sent in unannounced sorties to determine how porous American air defenses are.) In such a case, there may be combined visual and radar sightings by military and civilian observers and large numbers of independent reports. What is reported corresponds to no known aircraft. The Air Force and civilian aviation authorities truthfully state that none their aircraft was responsible. Even if they've been urging Congress to fund a southern Early Warning System, the Air Force is unlikely to admit that Soviet or Cuban aircraft got to New Orleans, much less Memphis, before anybody caught on.

Here again, we have every reason to expect a high-level technical investigating team, Air Force and civilian observers told to keep their mouths shut, and not just the appearance but the reality of suppression of data. Again, this conspiracy of silence need have nothing to do with alien spacecraft. Even decades later, there are bureaucratic reasons for the Department of Defense to be close-mouthed about such embarrassments. There is a potential conflict of interest between parochial concerns of the Department of Defense and the solution of the UFO enigma.

Government Conspiracies

One last excerpt from Sagan's "The Demon-Haunted World" about oft-lodged charge of the government's conspiracy of silence (p. 92-93). (Any more excerpts and I'll surely be charged with copyright infringement—please read the book for more! Though much lengthier excerpts are available for free on the Google Books version...)

A cover-up to keep knowledge of extraterrestrial life or alien abductions almost wholly secret for 45 years, with hundreds if not thousands of government employees privy to it, is a remarkable notion. Certainly, government secrets are routinely kept, even secrets of substantial general interest. But the ostensible point of such secrecy is to protect the country and its citizens. Here, though, it's different. The alleged conspiracy of those with security clearances is to keep from the citizens knowledge of a continuing alien assault on the human species. If extraterrestrials really were abducting millions of us, it would be much more than a matter of national security. It would impact the security of all human beings everywhere on Earth. Given such stakes, is it plausible that no one with real knowledge and evidence, in nearly 200 nations, would blow the whistle, speak out and side with the humans rather than the aliens?

Since the end of the Cold War NASA has been flailing about, trying to find missions that justify its existence—particularly a good reason for humans in space. If the Earth were being visited daily by hostile aliens, wouldn't NASA leap on this opportunity to augment is funding? And if an alien invasion were in progress, why would the Air Force, traditionally led by pilots, step back from manned spaceflight and launch all its payloads on unmanned boosters?

Consider the former Strategic Defense Initiative Organization, in charge of "Star Wars." It's fallen on hard times now [in 1996], particularly its objective of basing defenses in space. Its name and perspective have been demoted. It's the Ballistic Missile Defense Organization these days. It no longer even reports directly the Secretary of Defense. The inability of such technology to protect the United States against a massive attack by nuclear-armed missiles is manifest. But wouldn't we want at least to attempt deployment of defenses in space if we were facing an alien invasion?

The Department of Defense, like similar ministries in every nation, thrives on enemies, real or imagined. It is implausible in the extreme that the existence of such an adversary would be suppressed by the very organization that would most benefit from its presence. The entire post-Cold War posture of the military and civilian space programs of the United States (and other nations) speaks powerfully against the idea that there are aliens among us—unless, of course, the news is also being kept from those who plan the national defense. [No, please don't take the bait dangling in that last sentence…]

A Brief History of Observing the Sun

2011-02-08T06:15:00.001+07:00

A little history of sun-watching and science from our friends at the Solar Dynamics Observatory.

Source: Universe Today

Definisi Planet - Mengapa Pluto tidak termasuk kategori Planet?

2011-02-07T16:50:00.020+07:00

Mungkin beberapa tahun lalu, jumlah planet yang kita kenal ada 9, yaitu: Merkurius, Venus, Bumi, Mars, Jupiter, Saturnus, Uranus, Neptunus dan Pluto. Namun, tahukah Anda bahwa pada tahun 2006, International Astronomical Union (IAU) telah menentukan definisi planet yang baru. Imbas dari definisi planet yang baru ini sangat besar, karena Pluto yang sudah familiar dikenal sebagai sebuah planet akhirnya harus tersingkir dari "gelar"-nya. Tahukah Anda mengapa Pluto akhirnya "tersingkir"?

Planet, secara etimologis berarti pelancong (wanderer). Pada akhir abad ke-19, istilah Planet sudah menjadi istilah umum, meskipun belum ada batasan yang jelas mengenai kriteria suatu benda yang dapat dianggap sebagai planet. Umumnya, istilah "planet" diberikan kepada objek yang mengitari Matahari dan berukuran lebih besar daripada Pluto.

Setelah tahun 1992, astronomer telah menemukan banyak objek di luar orbit Neptunus (dikenal dengan istilah Trans-Neptunian Objects atau TNO) dan ratusan objek yang mengitari bintang lain (extrasolar planet, lihat artikel sebelumnya). Penemuan ini tidak hanya menambah jumlah dr objek yang potensial disebut planet, tetapi juga memperluas kenaekaragaman dan keanehan (peculiarity) dari objek-objek yang "masuk" kategori planet berdasarkan definisi/pengertian umum. Beberapa objek yang ditemukan tersebut ada yang lebih kecil daripada satelit Bumi, Bulan dan ada juga yang cukup besar untuk menjadi sebuah bintang. Penemuan - penemuan inilah yang membuat astronom merasa adanya kebutuhan untuk menentukan definisi dari sebuah Planet secara jelas agar tidak sembarang objek bisa dianggap sebagai planet.

Plot of the positions of all known Kuiper belt objects (green), set against the outer planets (blue)

Perlunya definisi yang jelas untuk Planet menjadi semakin jelas ketika ditemukannya TNO yang diberi nama Eris. Ukuran Eris lebih besar daripada ukuran Pluto, yang sebelumnya dianggap sebagai ukuran minimum untuk sebuah planet. Oleh sebab itu, pada bulan Agustus 2006, International Astronomical Union (IAU) mengadakan konferensi untuk membuat definisi baru Planet.

Eris as seen with the Hubble Space Telescope

DEFINISI PLANET BERDASARKAN IAU TAHUN 2006

The final definition, as passed on 24 August 2006 under the Resolution 5A of the 26th General Assembly is:

Illustration of the outcome of the vote

The IAU resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

(1) A planet [1] is a celestial body that:

(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects [3], except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

Footnotes:
[1] The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
[2] An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
[3] These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

The IAU further resolves:
Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of Trans-Neptunian Objects[1].

Footnote:
[1] An IAU process will be established to select a name for this category.
The IAU also resolved that "planets and dwarf planets are two distinct classes of objects", meaning that dwarf planets, despite their name, would not be considered planets

Penjelasan di atas adalah bunyi dari keputusan IAU mengenai definisi Planet yang baru. Secara sederhana, syarat- syarat sebuah objek dapat dikategorikan sebagai planet dalam tata surya ini jika:

mengitari Matahari
memiliki massa yang cukup untuk mencapai kondisi k esetimbangan hidrostatis (secara sederhana, objek yang sudah mencapai kondisi kesetimbangan hidrostatis memiliki bentuk bola sempurna).
telah "membersihkan objek-objek tetangga" dari orbitnya. atau dengan kata lain, massa Planet adalah massa yang dominan dibandingkan massa seluruh benda lain yang berada di orbit yang sama.

Sebuah objek yang tidak termasuk satelit dan hanya memenuhi dua syarat pertama akan diklasifikasikan sebagai dwarf planet (planet kerdil). Bagi objek yang hanya memenuhi syarat pertama (mengitari Matahari), akan disebut Small Solar System Body (SSSB) atau objek kecil di tata surya. Draft awal merencanakan akan memasukkan dwarf planet sebagai sub-kategori dari planet, tetapi karena keputusan ini akan mengakibatkan penambahan beberapa lusin objek ke dalam tata surya, draft ini dibatalkan. Di tahun 2006, yang termasuk dwarf planet adalah Ceres, Eris, Makemake, dan Pluto. Keputusan ini termasuk keputusan yang kontroversial dan menimbulkan dukungan dan kritik dari cukup banyak astronom, tetapi definisi inilah yang dipakai resmi hingga saat ini.

Jad, berdasarkan definisi yang baru ini, saat ini ada 8 planet yang diakui (Merkurius, Venus, Bumi, Mars, Jupiter, Saturnus, Uranus, dan Neptunus) dan ada lima planet kerdil (Pluto, Ceres, Eris, Makemake, dan Haumea). Definisi ini hanya berlaku untuk Tata Surya kita karena extrasolar Planet belum diketahui dengan jelas/akurat ukurannya. Extrasolar planets atau exoplanets akan didefinisikan dalam referensi lain, yang memisahkan/membedakan exoplanet dan dwarf stars (bintang kerdil).

Pertanyaan evaluasi:
1. Mengapa perlu adanya definisi baru untuk Planet?
2. Jelaskan definisi baru/syarat-syarat sebuah objek dijadikan Planet? Planet Kerdil?

Mendeteksi dan Menemukan Extrasolar Planet

2011-02-04T17:25:00.052+07:00

Belakangan ini banyak dibahas di berbagai media tentang penemuan planet di tata surya lain. Dalam artikel ini, akan dibahas beberapa teknik 'sederhana' yang digunakan astronom untuk menemukan planet di luar tata surya.

Seperti yang Anda ketahui bahwa bintang akan selalu terlihat sebagai point of light (sumber titik cahaya) meskipun menggunakan teleskop (kecuali untuk beberapa bintang yang besar dan 'dekat' dengan kita). Oleh sebab itu, dapat diperkirakan bahwa mengamati planet yang ada di bintang lain tentunya bukan perkara yang mudah.

Sebelum kita membahas bagaimana menemukan planet extrasolar (planet yang ada di luar tata surya kita), akan dibahas terlebih dahulu sekilas mengenai proses pembentukan planet.

SEJARAH SINGKAT TERBENTUKNYA PLANET

Semuanya berawal dari material awan debu. Tata surya (planetary system/sistem keplanetan) berasal dari awan berputar yang maha besar. Awan kabut itu (nebulae) mengerut di bawah gaya berat diri, membentuk piringan dengan protosurya yang sangat padat di pusat. Akibat pengerutan gravitasi suhu naik di dalam awan (pengerutan Kelvin Helmholtz). Di pusat kian sangat panas, lalu terpicu reaksi bom nuklir, dan pengerutan piringan akan berhenti.

Planet-planet terbentuk oleh akresi planetesimal dan akumulasi gas di dalam kabut surya. Planetesimal di tahap awal tatasurya, tabrakan dan akresi (saling menempel) membentuk protoplanet. Planet dari unsur-unsur berat terbentuk dan memadat di bagian dalam, suhu jadi lebih panas (di pusat), unsur-unsur ringan berdifusi ke tepi luar. Proses itu dikenal sebagai diferensiasi dari unsur-unsur.

Bintang yang masih muda (yang terbentuk di pusat akresi) tiba-tiba menyemburkan tenaga kuat, tenaga jet dan sangat singkat, dan membersihkan tata surya dari materi pembentuk planet yang tersisa. Bintang-bintang muda penyembur tenaga semacam itu dikenal sebagai Bintang-Bintang T Tauri .

Setelah itu, tata surya akan 'stabil'. Planet - planet butuh jutaan tahun untuk menggumpal dan membersihkan 'orbit'-nya serta mendingin hingga mencapai kondisi stabil.

PLANET DI TATA SURYA LAIN (EXTRASOLAR PLANETS)

Para astronom telah menemukan planet-planet mengorbit di bintang-bintang. Planet besar, seperti Yupiter, menarik bintang pusatnya ke dalam sehingga bintang terputar dalam satu orbit kecil mengitari titik pusat massa mereka. Planet yang mengorbit bintang lain itu disebut extrasolar planets.

Meski Planet sangat besar, tetap tak bisa dilihat, karena bintang sentral sangat terang. Namun, pergerakan kecil yang ditempuh bintang sentral karena gravitasi oleh planet, kadangkala dapat terdeteksi. Para astronom mengukur dengan teliti pergerakan bintang dengan memperhatikan sinarnya. Sinar bintang itu bergantian bergeser ke riak gelombang merah dan ke riak gelombang biru. Telah terdeteksi dengan cara itu lebih dari 100 extrasolar planet. Cara itu dikenal sebagai metode Pergeseran Doppler.

Beberapa planet yang sudah ditemukan:

OGLE-2005-BLG-390Lb planet extrasolar terkecil saat ini (2006). 188 extrasolar planet (18 April 2006) berbagai rentang massa dan periode orbit, namun planet sebesar massa Neptunus sangat sedikit/belum terdeteksi pada jarak > 0,15 SA dari bintang pusat. OGLE-2005-BLG-390Lb bermassa 5,5 (-2,7 to +5,5) massa bumi. Pada jarak pisah 2,6(-0,6 to +1,5) SA dari bintang kerdil-M bermassa 0,22(-0,11 to +0,21) massa matahari (68% rentang kepastian). Teori akresi planet meramalkan banyak planet bermassa lebih kecil daripada planet Neptunus ditemukan daripada planet raksasa Jupiter.

Jadi, ada banyak metode yang dapat digunakan oleh astronom untuk mendeteksi keberadaan planet/sistem keplanetan di bintang -bintang lain. Metode-metode tersebut antara lain:

Kecepatan radial (pergeseran Doppler)
Astrometri (proper motion, sangat terbatas)
Gravitasi Mikrolensa (planet dan bintang induk berada di depan bintang latar belakang)
Metode Transit (planet lewat di depan bintang induk)
Piringan Circumbintang (distorsi awan debu oleh planet yang mengorbit)
Pengamatan Direct (langsung) oleh teropong Spitzer.

1. METODE PERGESERAN DOPPLER (KECEPATAN RADIAL/KR)

Jika astrometri langsung mengamati bintang, maka metode KR, mengamati gerak bintang dari spektrum cahaya. Yakni secara sistematik memperhatikan pergeseran garis spektrum serapan dan pancaran. Dengan teleskop sekarang, hanya dapat diukur kecepatan sedikitnya 3 m/s. Bumi, misalnya hanya mempengaruhi gerak matahari sebesar 0.1 m/s. Dengan mengukur T dan mendapatkan massa bintang, m_BINTANG, bisa ditemukan 1/2 sumbu panjang orbit.

Jika massa bintang dapat diturunkan dari (mis. Diagram H-R) dan inklinasi orbit terhadap bidang ekliptika, i, diketahui, maka massa planet, m_P dapat dihitung dengan persamaan di bawah ini. Jika i tidak dapat diketahui, maka yang kita peroleh hanyalah m_P sin i.

Jadi sekarang kita sudah dapat menghitung massa planet (bila mengetahui inklinasi atau dengan mengambil asumsi).

Kecepatan radial untuk beberapa planet:
u/ Jupiter: v = 13 m/detik dan periode T = 12 tahun.
u/ Bumi : v = 0.09 m/detik dan periode T = 1 tahun
Limit deteksi hanya 3 m/detik, jadi planet-planet semacam Bumi sangat sulit teramati.

Penemuan pertama extrasolar planet terjadi di tahun 1995 di bintang 51 Pegasus.
Kini, lebih dari 120 planet seukuran Yupiter telah ditemukan di bintang-bintang lain dengan metode KR/Doppler. Orbit-orbitnya pendek, eksentrisitas tinggi serta harga massa mencapai setinggi 10 massa Yupiter.

2. METODE ASTROMETRI

Pertanyaannya: Dapatkah keberadaan planet seperti Jupiter diketahui dengan astrometri?

Sayang sekali, belum dapat. Mengapa? Mari kita lakukan perhitungan singkat.

Matahari mengorbit pusat gravitasi Matahari-Yupiter pada jejari orbit hanya 1.2 jejari matahari. 1.2 jejari matahari memetakan sudut sebesar 5.2 x 10^-3 detikbusur pada jarak 1 parsec – atau 5.2 x 10^-4 detikbusur pada jarak 10 pc. Kecermatan pengukuran hingga sudut sekecil itu masih belum dapat (sulit) dilakukan.

3. METODE MIKROLENSA (memanfaatkan sifat/fenomena gravitational lensing)

Gravitasi Mikrolensa terjadi jika planet dan bintang induk berada di depan bintang latar belakang.

4. METODE TRANSIT

Saat sebuah planet (benda gelap) melintas di depan bintang induknya, sebagian sinar bintang induknya akan terhalangi (ter-gerhana-i) oleh planet yang melintas. Peristiwa ini disebut transit planet (lihat diagram di bawah ini). Astronom akan mencari bintang2 yang kecerlangannya menurun secara periodik.

Jika sebuah bintang jauh di transit oleh sebuah planet semacam Yupiter, terjadi penurunan flux sinar sebesar 1% di bintang itu dari semulanya.

Sebuah planet yang telah ditemukan di bintang HD209458 dengan metode KR; pada tahun 1999, diamati kembali flux bintangnya. Ditemukan transit tepat pada waktu yang telah diramal sebelumnya. Seperti planet di 51Peg, planet itu besar dan mengorbit dekat sekali dengan bintang – planet semacam ini dikenali sebagai “hot Jupiters”.

Metode transit inilah yang digunakan oleh Teleskop Keppler. Teleskop ini dikhususkan untuk 'mencari' planet serupa Bumi. (penjelasan lebih detailnya silakan lihat di sini dan sini). Hasil kerja teleskop ini dapat dibaca pada link yang diberikan.

5. METODE PENGAMATAN LANGSUNG DENGAN TEROPONG SPITZER

KESIMPULAN

Metode KR hanya dapat mendeteksi planet-planet masif (sedikitnya 1/5 massa Yupiter) dengan periode relatif yang sangat pendek.
Kebanyakan planet-planet yang terdeteksi berada sangat dekat dengan bintang (kurang dari ~0.1SA)
3-4% bintang-bintang serupa matahari memiliki planet-planet jenis itu
Sejumlah kecil planet-planet yang lebih jauh umumnya mempunyai orbit yang lebih eksentrik (e >~0.2)

Planet-planet yang sudah ditemukan beserta informasi massa bintang induk dan periode orbitnya.

Bintang - bintang di angkasa ini sangat banyak. Bagaimana astronom dapat memilih bintang mana yang diamati/dicurigai memiliki sistem planet?

Sistem planet tidak bisa terbentuk pada bintang bintang yang luminositasnya besar. Hal ini disebabkan bintang-bintang seperti ini memiliki massa hidup yang cenderung singkat. Bintang-bintang generasi I (yang terbentuk dari material Big Bang) juga tidak mungkin memiliki sistem keplanetan karena kurangnya unsur-unsur berat. Jadi, bintang-bintang yang mungkin memiliki sistem keplanetan adalah bintang-bintang yang tidak terlalu panas dan termasuk Generasi ke dua atau lebih (bintang yang materialnya berasal dari sisa material bintang lain yang meledak lewat Supernova/hembusan saat pembentukan Planetary Nebulae).

LATIHAN

Sumber:
1. Materi pelatihan olimpiade Astronomi oleh Tim Astronomi ITB
2. Wikipedia

notes: jika ingin melihat gambar yang ada dengan lebih jelas, silakan klik di masing-masing gambar

SELAMAT BELAJAR

A Sense Of Planetary Scale

2011-01-31T16:40:00.004+07:00

Blogger Brad Goodspeed created an animation which shows different planets in our solar system as they would appear in the sky if it shared an orbit with our Moon, 380,000 km from earth. On his blog, he said he created it “to make you feel small.”

Source: Brad Goodspeed

Hubble Discovers Most Distant Galaxy Yet!

2011-01-27T10:42:00.007+07:00

Hubble Ultra Deep Field - Part D

No Princess is sending holographic help messages. No Hans Solo is warming up a Millenium Falcon to jump into hyperdrive. We don’t even have a Death Star waiting around the corner. But, what we do have is evidence that astronomers have pushed the Hubble Space Telescope to its limits and have seen further back in time than ever before. “We are looking back through 96% of the life of the universe, and in so doing, we have found just one galaxy, but it is one, but it is a remarkable object. The universe was only 500 million years old at that time versus it now being thirteen thousand-seven hundred million years old. ” said Garth Illingworth, Ames Research Scientist. We know about the Hubble Ultra Deep Field, but we invite you to boldy go on…

While studying ultra-deep imaging data from the Hubble Space Telescope, an international group of astronomers have found what may be the most distant galaxy ever seen, about 13.2 billion light-years away. “Two years ago, a powerful new camera was put on Hubble, a camera which works in the infrared which we had never really good capability before, and we have now taken the deepest image of the universe ever using this camera in the infrared.” said Garth Illingworth, professor of astronomy and astrophysics at the University of California, Santa Cruz. “We’re getting back very close to the first galaxies, which we think formed around 200 to 300 million years after the Big Bang.” The study pushed the limits of Hubble’s capabilities, extending its reach back to about 480 million years after the Big Bang, when the universe was just 4 percent of its current age. The dim object, called UDFj-39546284, is a compact galaxy of blue stars that existed 480 million years after the Big Bang, only four percent of the universe’s current age. It is tiny. Over one hundred such mini-galaxies would be needed to make up our Milky Way.

The farthest and one of the very earliest galaxies ever seen in the universe appears as a faint red blob in this ultra-deep–field exposure taken with NASA's Hubble Space Telescope. This is the deepest infrared image taken of the universe. Based on the object's color, astronomers believe it is 13.2 billion light-years away. (Credit: NASA, ESA, G. Illingworth (University of California, Santa Cruz), R. Bouwens (University of California, Santa Cruz, and Leiden University), and the HUDF09 Team)

Illingworth and UCSC astronomer Rychard Bouwens (now at Leiden University in the Netherlands) led the study, which will be published in the January 27 issue of Nature. Using infrared data gathered by Hubble’s Wide Field Planetary Camera 3 (WFC3), they were able to see dramatic changes in galaxies over a period from about 480 to 650 million years after the Big Bang. The rate of star birth in the universe increased by ten times during this 170-million-year period, Illingworth said. “This is an astonishing increase in such a short period, just 1 percent of the current age of the universe,” he said. There were also striking changes in the numbers of galaxies detected. “Our previous searches had found 47 galaxies at somewhat later times when the universe was about 650 million years old. However, we could only find one galaxy candidate just 170 million years earlier,” Illingworth said. “The universe was changing very quickly in a short amount of time.”

The Hubble Ultra Deep Field WFC3/IR Image. This Region of the Sky Contains the Deepest Optical and Near-Infrared Images Ever Taken of the Universe and is useful for finding star-forming galaxies at redshifts 8 and 10 (650 and 500 million years after the Big Bang, respectively). At UCSC and Leiden, we are using these data to better understand the properties of the first galaxies. Credit: Bouwen

According to Bouwens, these findings are consistent with the hierarchical picture of galaxy formation, in which galaxies grew and merged under the gravitational influence of dark matter. “We see a very rapid build-up of galaxies around this time,” he said. “For the first time now, we can make realistic statements about how the galaxy population changed during this period and provide meaningful constraints for models of galaxy formation.” Astronomers gauge the distance of an object from its redshift, a measure of how much the expansion of space has stretched the light from an object to longer (“redder”) wavelengths. The newly detected galaxy has a likely redshift value (“z”) of 10.3, which corresponds to an object that emitted the light we now see 13.2 billion years ago, just 480 million years after the birth of the universe. “This result is on the edge of our capabilities, but we spent months doing tests to confirm it, so we now feel pretty confident,” Illingworth said.

The galaxy, a faint smudge of starlight in the Hubble images, is tiny compared to the massive galaxies seen in the local universe. Our own Milky Way, for example, is more than 100 times larger. The researchers also described three other galaxies with redshifts greater than 8.3. The study involved a thorough search of data collected from deep imaging of the Hubble Ultra Deep Field (HUDF), a small patch of sky about one-tenth the size of the Moon. During two four-day stretches in summer 2009 and summer 2010, Hubble focused on one tiny spot in the HUDF for a total exposure of 87 hours with the WFC3 infrared camera.

“NASA continues to reach for new heights, and this latest Hubble discovery will deepen our understanding of the universe and benefit generations to come,” said NASA Administrator Charles Bolden, who was the pilot of the space shuttle mission that carried Hubble to orbit. “We could only dream when we launched Hubble more than 20 years ago that it would have the ability to make these types of groundbreaking discoveries and rewrite textbooks.”

To go beyond redshift 10, astronomers will have to wait for Hubble’s successor, the James Webb Space Telescope (JWST), which NASA plans to launch later this decade. JWST will also be able to perform the spectroscopic measurements needed to confirm the reported galaxy at redshift 10. “It’s going to take JWST to do more work at higher redshifts. This study at least tells us that there are objects around at redshift 10 and that the first galaxies must have formed earlier than that,” Illingworth said.

“After 20 years of opening our eyes to the universe around us, Hubble continues to awe and surprise astronomers,” said Jon Morse, NASA’s Astrophysics Division director at the agency’s headquarters in Washington. “It now offers a tantalizing look at the very edge of the known universe — a frontier NASA strives to explore.” How far back will we go? If you sit around a campfire watching the embers climb skywards and discuss cosmology after an observing night with your astro friends, someone will ultimately bring up the topic of space/time curvature. If you put an X on a balloon and expand it – and trace round its expanse – you will eventually return to your mark. If we see our beginnings, will we also eventually see our end coming up over the horizon? Wow… Pass the marshmallows, please. We’ve got a lot to think about.

Reader Info: Illingworth’s team maintains the First Galaxies website, with information about the latest research on distant galaxies. In addition to Bouwens and Illingworth, the coauthors of the Nature paper include Ivo Labbe of Carnegie Observatories; Pascal Oesch of UCSC and the Institute for Astronomy in Zurich; Michele Trenti of the University of Colorado; Marcella Carollo of the Institute for Astronomy; Pieter van Dokkum of Yale University; Marijn Franx of Leiden University; Massimo Stiavelli and Larry Bradley of the Space Telescope Science Institute; and Valentino Gonzalez and Daniel Magee of UC Santa Cruz. This research was supported by NASA and the Swiss National Science Foundation. Hubble Ultra Deep Field Image and Video courtesy of NASA/STSci.

Source: Universe Today

Short Quiz:
Can you calculate the velocity of that distant galaxy (UDFj-39546284) moving away from us? and, why is the more distant galaxy is younger than the closer one?

Tipe - Tipe Galaksi

2010-12-08T13:13:00.004+07:00

Dengan mempergunakan teleskop 250 cm di Observatorium Mount Palomar, astronom Edwin Hubble (1924) memotret sebuah galaksi di rasi Andromeda. Dia menjelaskan, untuk ertama kalinya, bentuk galaksi yang kemudian terkenal dengan nama galaksi Andromeda, berjarak 2 juta tahun cahaya dari galaksi kita (Bimasakti/Milkyway). Galaksi Andromeda merupakan galaksi luar (extra galaxy) pertama yang diketahui astronom. Sejak penemuannya, banyak studi dilakukan dalam mempelajari galaksi-galaksi di luar galaksi Bimasakti tempat kita berada.

Upaya para astronom mempelajari galaksi melalui pengamatan semenjak abad ke-18, telah melahirkan berbagai katalog benda-benda langit yang meliputi gugusan bintang termasuk didalamnya adalah galaksi. Pada tahun 1888, J.L.E. Dreyer mempublikasikan New General Catalogue of nebulae and Clusters of Stars yang memuat 7840 obyek langit. Katalog ini dilengkapi dengan suplemennya, Index Catalogues pada tahun 1895 dan 1908. Umumnya katalog tersebut mempergunakan notasi NGC atau IC diikuti dengan nomor obyek dalam daftar. Sebagai contoh, galaksi Andro-meda diberi nomor katalogus NGC 224.

Ada banyak galaksi-galaksi dengan berbagai ragam bentuknya. Hubble mengklasifikasikan galaksi-galaksi berdasarkan bentuknya ke dalam 3 kelompok utama, yakni:

1. Galaksi spiral (S)
Populasi galaksi berbentuk spiral ini yang terbanyak (80%). Galaksi ini memiliki struktur yang paling teratur dengan pusat, selubung bulat dan piringan dengan lengan spiral yang mengelilingi ekuator galaksi. Variasi dari galaksi spiral adalah galaksi spiral berbatang (SB), dengan bentuk cerutu yang melintasi pusat dan di kedua ujungnya pola spiral menjuntai.

2. Galaksi eliptik (E)
Galaksi dengan bentuk ini meliputi 17% dari seluruh populasi galaksi di alam semesta. Bentuknya lebih sederhana dibandingkan dengan galaksi spiral, karena hanya terdiri dari pusat dan selubung pipih. Kerapatan bintang lebih tinggi di pusat dibanding di tepiannya.

3. Galaksi tidak beraturan
Sebanyak 3% dari galaksi yang teramati sejauh ini menunjukkan bentuk yang tidak beraturan. Bentuknya lebih merupakan onggokan bintang dengan batas yang kurang jelas. Berbagai contoh nyata galaksi ini antara lain Awan Magellan kecil dan besar, tetangga galaksi kita, Bima Sakti.
Pola galaksi yang dirangkum dan diklasifikasikan oleh Hubble ditafsirkannya sebagai perjalanan evolusi galaksi di alam semesta dari bentuk yang awalnya sangat teratur menuju bentuk yang tidak beraturan.

Soal - soal Latihan

2010-11-21T06:07:00.003+07:00

1. Bulan memerlukan waktu paling tidak 2 menit untuk terbit dilihat dari Bumi. Berapa lama Bumi memerlukan waktu untuk terbit dilihat oleh seorang pengamat dari Bulan?
a. 2 menit
b. 4 menit
c. 6 menit
d. 8 menit
e. Bumi tidak terbit dan tidak tenggelam

2. On the sunlit side of the Moon the sky appears …
A. white because of the extreme brilliance of the sunlight
B. black because the Earth blocks the light
C. blue due to the Moons' atmosphere
D. black because the Moon lacks an atmosphere
E. black because the Moon has a dense atmosphere

3. You are adrift at sea, and you see a star directly overhead. You remember from your astronomy lab at N.C. State that this star has a declination of 42 degrees South, and a Right Ascension of 8 hours. From this information alone, you know that …
A) You are adrift at a point north latitude 42 degrees.
B) You are adrift at a point south latitude 42 degrees.
C) You are adrift at a point west longitude 8 degrees.
D) You are adrift at a point south latitude 48 degrees.
E) A and C

4. If you lived on the Moon, would the motion of the planets appear any different than from Earth?
A. The motion of the planets would not appear significantly different than on the Earth.
B. The planets would not appear to go around the Moon.
C. The planets would not appear to go around the Earth.
D. The planets would not appear to go around the Sun.
E. None of the above

5. You are carried away by an alien spacecraft to a different star planetary system. You are set down on a planet with cloudless skies. After some time, you notice five planets in the sky. Three retrograde after greatest eastern elongation with the "sun"; two at opposition. From this observation, you infer that, in a heliocentric model, you are on the _____ planet outward from the "sun".
A. first
B. second
C. third
D. fourth
E. fifth

6. When Venus sets after sunset …
a. Venus is west of the sun
b. Venus is east of the sun
c. Venus could be either east or west of the sun depending on the month.
d. it is a mistake because Venus never sets after sunset
e. it must be moving retrograde

7. Pernyataan tentang gerak planet yang tepat adalah ...
A. Planet Venus mungkin saja terlihat saat tengah malam
B. Planet Jupiter tidak mungkin tertutup oleh bulan Purnama
C. Planet Mars selalu nampak berdekatan dengan Matahari
D. Planet Merkurius tidak mungkin nampak melintas di depan piringan Matahari
E. Planet Saturnus bisa mengalami gerak retrogade

8. Peristiwa yang tidak tepat berhubungan dengan pengamat yang ada tepat di kutub utara adalah ...
A. Matahari paling tinggi ada di 23,50 di atas horizon
B. Pada bulan Desember, Matahari tidak terbit
C. Semua arah adalah arah selatan
D. Bisa mengamati rasi Centaurus di bulan-bulan tertentu
E. Bintang Polaris menjadi bintang sirkumpolar

Selamat Belajar

Solar System

2010-11-08T21:52:00.006+07:00

A couple videos related to the solar system:

Source: youtube

Latihan Soal: Gerak Benda Langit

2010-11-02T14:04:00.001+07:00

1. Tentukan perbandingan gaya pasang surut antara Bumi-Bulan dan Bumi-Matahari bila diketahui jarak pusat ke pusat antara Bumi-Matahari 400 kali jarak pusat ke pusat Bumi-Bulan, diameter Bumi 4 kali diameter Bulan, dan massa Bumi 80 kali massa Bulan!

2. Sebuah satelit mempunyai orbit polar dengan ketinggian 5,49 x 10^6 m di atas permukaan Bumi. Setelah melewati di atas London, tentukan posisi satelit saat menyelesaikan satu kali orbit!

3. Mengapa objek langit yang besar (misalkan Matahari, Bintang, Planet, dll) bentuknya mendekati bola sedangkan objek langit yang relatif kecil (misalkan Asteroid, Komet, dll) bentuknya irregular?

4. Certain neutron stars are believed to be rotating at about 1 revolution/second. If such a star has a radius of 20 km, what must be its minimum mass so that material on its surface remains in place during the rapid rotation?

5. Planet imajiner mempunyai jarak rata-rata 120 satuan astronomi dari matahari. Berapa lama waktu yang diperlukan planet ini untuk mengorbit matahari? Berapa periode sinodisnya?

Selamat Belajar.

Introducing Lomba Rancang Pabrik Tingkat Nasional

2010-09-24T20:29:00.004+07:00

Memperkenalkan website www.lrptn.com sebagai sumber informasi bagi acara Lomba rancang Pabrik Tingkat Nasional.

Sekilas mengenai LRPTN (Source: www.lrptn.com)

Perkembangan industri kimia saat ini tidak lepas dari kemampuan dan kreativitas para insinyurnya, yang selalu memberikan ide-ide baru sehingga dapat memenuhi kebutuhan masyarakat. Kecakapan seorang insinyur tentunya tidak diperoleh secara instan, namun perlu dibentuk semenjak duduk di bangku kuliah. Untuk meningkatkan kemampuan dan kreativitas para calon insinyur teknik kimia, Himpunan Mahasiswa Teknik Kimia (HIMATEK) ITB bekerjasama dengan Program Studi Teknik Kimia ITB mengadakan Lomba Rancang Pabrik Tingkat Nasional (LRPTN). LRPTN merupakan sebuah kompetisi rancang pabrik yang mengangkat tema-tema yang berkaitan dengan isu-isu aktual dalam dunia industri. Sampai sekarang, LRPTN telah berhasil diselenggarakan sebanyak 11 kali sejak tahun 1996.

LRPTN yang pertama kali diadakan diikuti oleh 8 kelompok peserta dari berbagai perguruan tinggi di Indonesia dengan dewan juri terpillih, yang memiliki kompetensi dalam menilai rancangan suatu pabrik dari sudut pandang keilmuan, khususnya Teknik Kimia. Rangkaian acara LRPTN diisi oleh pembicara-pembicara yang secara khusus diundang untuk berbagi pengetahuan dan pengalaman menarik mereka berkaitan dengan tema dari tiap LRPTN. Semenjak LRPTN IV pada tahun 2000, kompetisi ini dikategorikan menjadi 2, yaitu kategori perancangan pabrik dan problem solving. Kategori perancangan pabrik ini dilombakan dengan pembatasan berdasarkan subtema utama dari LRPTN, sedangkan untuk kategori problem solving dilombakan untuk memfasilitasi ide-ide solutif dan inovatif dari mahasiswa dalam memecahkan masalah nyata yang sedang terjadi dalam suatu pabrik tertentu.

Selanjutnya, pada LRPTN V yang diselenggarakan pada tahun 2001, kategori LRPTN diubah menjadi 3 kategori, yaitu Lomba Rancang Pabrik Kategori A, Lomba Rancang Pabrik Kategori B, dan problem solving. “ Format kompetisi LRPTN dengan 3 kategori tersebut dianggap mampu memfasilitasi ide-ide solutif dan inovatif dari mahasiswa sehingga penyelenggaraan LRPTN berikutnya, mulai dari LRPTN VII hingga LRPTN XI mengikuti format yang hampir sama dengan LRPTN V. Banyak pihak memandang LRPTN merupakan suatu kegiatan yang memberi dampak positif bagi perkembangan mahasiswa Teknik Kimia di Indonesia dalam meningkatkan kemampuan aplikatif mahasiswa dalam melakukan suatu pra rancangan pabrik. Hal ini ditunjukkan dengan peningkatan jumlah peserta yang turut bergabung untuk mengikuti LRPTN ini tiap tahunnya.

Penyelenggaraan LRPTN diharapkan dapat menjadi suatu wadah berkarya bagi mahasiswa se-Indonesia dalam lingkup keilmuan Teknik Kimia. Selain itu, LRPTN ini juga diharapkan dapat memberikan kontribusi nyata bagi perkembangan industri nasional.

Hubble 20 years of Space-Shattering Discoveries

2010-05-07T00:46:00.005+07:00

A nice video from NASA to celebrate 20 years of Hubble Telescope.

Source: youtube.com

Soal Latihan Astronomi Dasar

2010-05-07T00:41:00.002+07:00

Silakan mencoba beberapa latihan soal Astronomi.

1. If you measure the parallax of a star to be 0,5 arc seconds on Earth and an observer in a space station in the orbit around the Sun measures a parallax for the same star to be 1 arc seconds, how far is the space station from the Sun ?

2. Sebuah galaksi yang berada pada jarak d Mpc dari kita. Tunjukkan bahwa pada galaksi ini, bentangan 1” di langit berkorespondensi dengan bentangan fisik 5d parsec!

3. Para ahli menggunakan sinar laser untuk menentukan jarak dari Bumi ke planet Venus. Sinar laser ditembakkan ke arah planet Venus , lalu para ahli mengukur selang waktu antara penembakkan sinar laser dengan pantulan yang diterima oleh detektor tertentu. Jika didapat selang waktunya adalah 4,32178 menit. Hitunglah jarak planet Venus dari Bumi !

4. Teleskop di Bumi mempunyai kemampuan memisahkan objek (resolving power) sebesar 0”,1. Berapakah ukuran kawah minimum yang dapat diamati di permukaan Mars ?

5. You observe an asteroid approaching the Earth. You have two observatories 3200 km apart, so you can measure the parallax shift of the incoming asteroid. You observe the parallax shift to be 0,022 degrees.
a) How big is the parallax shift in radians ?
b) How far away is the asteroid ?

Selamat belajar.

Sekilas Tentang Badai Matahari

2010-03-14T06:47:00.004+07:00

Matahari adalah sumber dari semua energi yang kita kenal di Bumi. Jika kita merunut semua sumber energi yang kita kenal dan kita gunakan sehari-hari, semuanya akan bermuara pada Matahari. Matahari sendiri menghasilkan energi lewat reaksi nuklir yang terjadi di pusatnya. Namun, meski Matahari memegang peran penting sebagai sumber energi yang kita butuhkan, Matahari juga menyimpan potensi yang bisa memberikan ancaman bagi manusia dan ekosistem Bumi. Ancaman yang dimaksud adalah peristiwa yang dikenal dengan nama badai matahari.

Gambar 1. Struktur Matahari

Sebelum membicarakan tentang badai matahari, kita akan melihat sekilas tentang Matahari. Matahari adalah sebuah bintang, yaitu bola plasma panas yang ditopang oleh gaya gravitasi. Di pusat Matahari (nomor 1 dalam Gambar 1), terjadi reaksi nuklir (fusi) yang mengubah 4 atom hidrogen menjadi 1 atom helium. Reaksi fusi tersebut, selain menghasilkan helium, juga menghasilkan energi dalam jumlah melimpah (ingat persamaan terkenal oleh Einstein: E=mc²). Energi yang dihasilkan, di pancarkan keluar melewati bagian-bagian Matahari, yaitu: zona radiatif (nomor 2), zona konventif (nomor 3), dan bagian atmosfer Matahari, yang terdiri dari fotosfer (nomor 4), kromosfer (nomor 5), dan korona (nomor 6). Dan badai Matahari adalah peristiwa yang berkaitan dengan bagian atmosfer Matahari tersebut.

Bagian terluar dari Matahari, yaitu korona, memiliki temperatur yang mencapai jutaan kelvin. Dengan temparatur yang tinggi tersebut, materi yang berada di korona Matahari memiliki energi kinetik yang besar. Tarikan gravitasi Matahari tidak cukup kuat untuk mempertahankan materi korona yang memiliki energi kinetik yang besar itu dan secara terus menerus, partikel bermuatan yang berasal dari korona, akan lepas keluar angkasa. Aliran partikel ini dikenal dengan nama angin matahari, yang terutama terdiri dari elektron dan proton dengan energi sekitar 1 keV. Setiap tahunnya, sebanyak 10¹² ton materi korona lepas menjadi angin matahari, yang bergerak dengan kecepatan antara 200-700 km/s.

Berbeda dengan pusat Matahari yang relatif sederhana, bagian atmosfer Matahari relatif lebih rumit. Karena di atmosfer Matahari ini, medan magnetik Matahari berperan besar terhadap berbagai peristiwa yang terjadi di dalamnya. Ada berbagai fenomena menarik diamati di atmosfer Matahari berkaitan dengan medan magnetik Matahari, seperti bintik matahari (sun spot), ledakan Matahari (solar flare), prominensa, dan pelontaran material korona (CME – Coronal Mass Ejection). Hal-hal inilah yang berkaitan dengan badai matahari.

Jadi apa yang dimaksud dengan badai matahari?

Singkatnya, badai matahari adalah kejadian/event dimana aktivitas Matahari berinteraksi dengan medan magnetik Bumi. Badai matahari ini berkaitan langsung dengan peristiwa solar flare dan CME. Kedua hal itulah yang menyebabkan terjadinya badai matahari.

Solar flare adalah ledakan di Matahari akibat terbukanya salah satu kumparan medan magnet permukaan Matahari. Ledakan ini melepaskan partikel berenergi tinggi dan radiasi elektromagnetik pada panjang gelombang sinar-x dan sinar gamma. Partikel berenergi tinggi yang dilepaskan oleh peristiwa solar flare, jika mengarah ke Bumi, akan mencapai Bumi dalam waktu 1-2 hari. Sedangkan radiasi elektromagnetik energi tingginya, akan mencapai Bumi dalam waktu hanya sekitar 8 menit.

Lalu bagaimana dengan CME?

CME adalah pelepasan material dari korona yang teramati sebagai letupan yang menyembur dari permukaan Matahari. Dalam semburan material korona ini, sekitar 2×10¹¹ – 4×10¹³ kilogram material dilontarkan dengan energi sebesar 10²² – 6×10²⁴ joule. Material ini dilontarkan dengan kecepatan mulai dari 20 km/s sampai 2000 km/s, dengan rata-rata kecepatan 350 km/s. Untuk mencapai Bumi, dibutuhkan waktu 1-3 hari.

Matahari kita memiliki siklus keaktifan dengan periode sekitar 11 tahun. Siklus keaktifan ini berkaitan dengan pembalikan kutub magnetik di permukaan Matahari. Keaktifan Matahari ini bisa dilihat dari jumlah bintik matahari yang teramati. Saat keaktifan Matahari mencapai maksimum, kita akan mengamati bintik matahari dalam jumlah paling banyak di permukaan Matahari dan pada saat keaktifan Matahari mencapai maksimum inilah, angin matahari lebih ‘kencang’ dari biasanya dan partikel-partikel yang dipancarkan juga lebih energetik. Dan peristiwa solar flare dan CME dalam skala besar juga lebih dimungkinkan untuk terjadi. Dengan kata lain, saat keaktifan Matahari mencapai maksimum, Bumi akan lebih banyak dipapar dengan partikel-partikel bermuatan tinggi (lebih tinggi dari biasanya) dan radiasi elektromagnetik energi tinggi.

Partikel-partikel bermuatan yang dipancarkan dari peristiwa solar flare dan CME, saat mencapai Bumi, akan berinteraksi dengan medan magnetik Bumi. Interaksi ini akan menyebabkan gangguan pada medan magnetik Bumi buat sementara.

Saat partikel-partikel bermuatan dengan energi tinggi mencapai Bumi, ia akan diarahkan oleh medan magnetik Bumi, untuk bergerak sesuai dengan garis-garis medan magnetik Bumi, menuju ke arah kutub utara dan kutub selatan magnetik Bumi. Saat partikel-partikel energetik tersebut berbenturan dengan partikel udara dalam atmosfer Bumi, ia akan menyebabkan partikel udara (terutama nitrogen) terionisasi. Bagi kita yang berada di permukaan Bumi, yang kita amati adalah bentuk seperti tirai-tirai cahaya warna-warni di langit, yang dikenal dengan nama aurora. Aurora ini bisa diamati dari posisi lintang tinggi di sekitar kutub magnetik Bumi (utara dan selatan).

Gambar 2. Aurora

Saat terjadi badai matahari, partikel-partikel energetik tadi tidak hanya menghasilkan aurora yang indah yang bisa di amati di lintang tinggi. Tapi bisa memberikan dampak yang relatif lebih besar dan lebih berbahaya. Dampak yang dimaksud antara lain: gangguan pada jaringan listrik karena transformator dalam jaringan listrik akan mengalami kelebihan muatan, gangguan telekomunikasi (merusak satelit, menyebabkan black-out frekuensi HF radio, dll), navigasi, dan menyebabkan korosi pada jaringan pipa bawah tanah.

Peristiwa gangguan besar yang disebabkan oleh badai matahari, yang paling terkenal adalah peristiwa tahun 1859, peristiwa yang dikenal dengan nama Carrington Event. Saat itu, jaringan komunikasi telegraf masih relatif baru tapi sudah luas digunakan. Ketika terjadi badai Matahari tahun 1859, jaringan telegraf seluruh Amerika dan Eropa mati total. Aurora yang biasanya hanya bisa diamati di lintang tinggi, saat itu bahkan bisa diamati sampai di equator.

Masih ada beberapa contoh peristiwa lain yang berkaitan dengan badai matahari yang terjadi dalam abad ke-20 dan 21:

13 maret 1989: Terjadi CME besar 4 hari sebelumnya. Badai geomagnetik menghasilkan arus listrik induksi eksesif hingga ribuan ampere pada sistem interkoneksi kelistrikan Ontario Hydro (Canada). Arus induksi eksesif ini menyebabkan sejumlah trafo terbakar. Akibat dari terbakarnya trafo tsb, jaringan listrik di seluruh Quebec (Canada) putus selama 9 jam. Guncangan magnetik badai sekitar seperempat Carrington event, (sekitar 400 nT). Aurora teramati sampai di Texas
Januari 1994 : 2 buah satelit komunikasi Anik milik Canada rusak akibat digempur elektron-elektron energetik dari Matahari. Satu satelit bisa segera pulih dalam waktu beberapa jam, namun satelit lainnya baru bisa dipulihkan 6 bulan kemudian.
Total kerugian akibat lumpuhnya satelit ini disebut mencapai US $ 50 – 70 juta.
November 2003 : Mengganggu kinerja instrumen WAAS berbasis GPS milik FAA AS selama 30 jam.
Januari 2005: Berpotensi mengakibatkan black-out di frekuensi HF radio pesawat, sehingga penerbangan United Airlines 26 terpaksa dialihkan menghindari rute polar (kutub) yang biasa dilaluinya.

Badai Matahari juga bisa berbahaya bagi makhluk hidup secara biologi. Bahaya ini terutama bagi para astronot yang kebetulan sedang berada di luar angkasa saat badai matahari terjadi. Bagi kita yang berada di permukaan Bumi, kita relatif aman terlindungi oleh medan magnetik Bumi. Pengaruh langsung dari badai matahari ini hanya dialami oleh binatang-binatang yang peka terhadap medan magnetik Bumi. Karena badai matahari mengganggu medan magnetik Bumi, maka binatang-binatang yang peka terhadap medan magnetik akan secara langsung terimbas. Misalnya burung-burung, lumba-lumba, dan paus, yang menggunakan medan magnetik Bumi untuk menentukan arah, untuk sesaat ketika badai matahari terjadi, mereka akan kehilangan arah.

Saat ini, Matahari sedang menuju puncak keaktifan dalam siklusnya yang ke-24. Puncak keaktifan Matahari ini diperkirakan terjadi sekitar tahun 2011-2013. Saat puncak keaktifan Matahari pada siklus ke-24 ini, diperkirakan tidak akan jauh berbeda dengan saat puncak keaktifan pada siklus-siklus sebelumnya. Mungkin efeknya akan sedikit lebih besar, tapi ada juga yang menduga akan terjadi hal yang sebaliknya, justru lebih kecil efeknya. Yang manapun itu kasusnya, bisa dikatakan semua ahli fisika matahari sepakat tidak mungkin terjadi peristiwa besar yang akan membahayakan kehidupan di muka Bumi.

Berdasarkan pengetahuan kita saat ini, badai matahari hanya akan memberikan ancaman bahaya yang rendah. Solar flare dan CME yang terjadi di Matahari, tidak akan cukup untuk menyebabkan peristiwa seperti yang digambarkan dalam beberapa film yang beredar belakangan ini. Beberapa bintang yang diamati memang menunjukkan adanya peristiwa yang dikenal dengan istilah superflare, yaitu flare seperti yang kita amati di Matahari tapi dengan intensitas yang jauh lebih besar. Tapi peristiwa serupa diduga bukan peristiwa yang umum dan diragukan bakal terjadi pada Matahari kita, setidaknya saat ini. Memang peristiwa solar flare dan CME belum bisa diprediksi dengan baik untuk saat ini. Tapi pengetahuan kita yang didapat dari pengamatan Matahari lewat berbagai observatorium landas-bumi dan wahana antariksa yang terus menerus mengamati Matahari, kita semakin mengerti berbagai peristiwa yang terjadi di Matahari. Setidaknya untuk saat ini, kita bisa mengatakan dengan cukup yakin bahwa yang digambarkan dalam film-film fiksi ilmiah (misalnya: film 2012) tentang badai raksasa matahari, tidak akan terjadi dalam waktu dekat.

Seiring dengan perkembangan teknologi elektronika, serta kaitannya dengan iklim, studi tentang aktivitas matahari menjadi perhatian yang semakin perlu dikaji. Bisakah kita memprediksi badai matahari? Dinamika siklusnya? Dinamika cuaca antariksa yang di dorong dinamika matahari? Pengamatan matahari saat ini telah menggunakan teknologi satelit dalam menentukan bilamanakah terjadi aktivitas yang tiba-tiba dari matahari.

SOHO (Solar Heliospheric Observatory), diluncurkan untuk terus menerus memonitor matahari; ACE (Advance Composition Explorer), mengamati perubahan lingkungan antariksa dan memberikan peringatan adanya badai matahari, satu jam sebelum mencapai bumi. WIND yang mengawasi angin matahari yang terjadi pada ruang antar planet sekitar bumi, atau IMAGE (Imager for Magnetopause-to-Auroral Global Exploration) mengamati partikel bermuatan dan atom netral disekitar magnetosfer. Kesemuanya itu digunakan untuk memahami fenomena yang terjadi pada matahari dan keterkaitannya dengan lingkungan bumi. Tetapi pemahaman yang lebih baik lagi akan diperoleh jika kita bisa memahami bagaimana dinamika yang sesungguhnya terjadi jauh di dalam matahari, dan mendorong terjadinya dinamika yang teramati. Dan dengan dukungan pengamatan yang semakin baik, kajian yang semakin mendalam mendorong semakin berkembangnya studi bidang astronomi, khusunya astrofisika bintang/matahari. (Gambar dari SOHO ditampilkan pula di dalam blog ini, di bagian kanan)

Sumber: www.langitselatan.com

Soal - soal latihan astronomi 2

2010-03-02T07:32:00.002+07:00

Silakan mencoba kedua soal di bawah ini. Soal-soal ini merupakan soal olimpiade astronomi siswa di India.

1. Jayshree claimed that she saw a solar eclipse when the size of the solar disk was 26’ and that of the lunar disk was 30′. She also claimed that at the time of the maximum eclipse, distance between the centres of the two disks was 7′. Qualitatively show that she could not have observed a total eclipse. Find the percentage of the solar disk covered at the time of the maximum eclipse.

2. A year in Solar calendar consist of 365.25 days and the same in Lunar calendar consist of 354 days. The additional days in Solar calendar are kept as balance every year. Whenever the number of balance days exceeds 30, an additional month of 30 days is added to the lunar year to offset the difference. The cycle goes on. Anwesh, whose birthday falls on 1st January, noticed that in the year 2008, his birthday coincided with the start of the lunar year. In which earliest future year, his birthday will again coincide with the start of the lunar year?

Solusinya dapat di download di sini

Where did today’s spiral galaxies come from?

2010-02-09T12:39:00.003+07:00

Hubble shows that the beautiful spirals galaxies of the modern Universe were the ugly ducklings of six billion years ago.

If confirmed, the finding highlights the importance to many galaxies of collisions and mergers in the recent past. It also provides clues for the unique status of our own galaxy, the Milky Way. Using data from the NASA/ESA Hubble Space Telescope, astronomers have created a census of galaxy types and shapes from a time before Earth and the Sun existed, up to the present day. The results show that, contrary to contemporary thought, more than half of the present-day spiral galaxies had peculiar shapes as recently as 6 billion years ago.

The study of the shapes and formation of galaxies, known as morphology, is a critical and much-debated topic in astronomy. An important tool for this is the ‘Hubble sequence’ or the ‘Hubble tuning-fork diagram’, a classification scheme invented in 1926 by the same Edwin Hubble in whose honour the space telescope is named.

Hubble’s scheme divides regular galaxies into three broad classes — ellipticals, lenticulars and spirals — based on their visual appearance. A fourth class contains galaxies with an irregular appearance.

A team of European astronomers led by François Hammer of the Observatoire de Paris has, for the first time, completed a census of galaxy types at two different points in the Universe’s history — in effect, creating two Hubble sequences — that help explain how galaxies form. In this survey, researchers sampled 116 local galaxies and 148 distant galaxies.

The astronomers show that the Hubble sequence six billion years ago was very different from the one that astronomers see today. “Six billion years ago, there were many more peculiar galaxies than now – a very surprising result,” says Rodney Delgado-Serrano, lead author of the related paper recently published in Astronomy & Astrophysics. “This means that in the last six billion years, these peculiar galaxies must have become normal spirals, giving us a more dramatic picture of the recent Universe than we had before.” The astronomers think that these peculiar galaxies did indeed become spirals through collisions and merging. Although it was commonly believed that galaxy mergers decreased significantly eight billion years ago, the new result implies that mergers were still occurring frequently after that time — up to as recently as four billion years ago. “Our aim was to find a scenario that would connect the current picture of the Universe with the morphologies of distant, older galaxies — to find the right fit for this puzzling view of galaxy evolution,” says Hammer.

Also contrary to the widely held opinion that galaxy mergers result in the formation of elliptical galaxies, Hammer and his team support a scenario in which these cosmic clashes result in spiral galaxies. In a parallel paper published in Astronomy & Astrophysics, they delve further into their ‘spiral rebuilding’ hypothesis, which proposes that peculiar galaxies affected by gas-rich mergers are slowly reborn as giant spirals with discs and central bulges. Although our own Galaxy is a spiral galaxy, it seems to have been spared much of the drama; its formation history has been rather quiet and it has avoided violent collisions in astronomically recent times. However, the large Andromeda Galaxy from our neighbourhood has not been so lucky and fits well into the ‘spiral rebuilding’ scenario. Researchers continue to seek explanations for this.

Notes for editors:

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Hammer and his team used data from the Sloan Digital Sky Survey undertaken by Apache Point Observatory, New Mexico, USA, and from the GOODS field and Hubble Ultra Deep Field taken by the Advanced Camera for Surveys aboard Hubble.

R. Delgado-Serrano, et al., 2010, How was the Hubble Sequence 6 Giga-years ago? Astronomy & Astrophysics, 509, A78.

F. Hammer et al., 2009, The Hubble Sequence: just a vestige of merger events? Astronomy & Astrophysics, 507, 1313.

Source: ESA

Close Up Pictures Of Pluto's Face

2010-02-06T18:35:00.003+07:00

Since discovered in 1930, there has never been observed which can provide a detailed picture of the face of Pluto. Although Pluto is an interesting object, even a topic of debate will be the definition of Pluto in 2006; but Pluto is still difficult to observe and record the details, because a small and distant.

However, Hubble Space Telescope (HST), has changed all that. With the observations that have been conducted since 1994, until the recent images taken between the years 2002-2003, then obtained a more detailed picture of Pluto, rather than observations that have been made ever. These results are a long way from the details, because the challenge to record details such as a soccer ball from a distance of 60 km.

Change the face of Pluto Hubble Space Telescope is seen. Credit: Hubble

Although the image of the HST is not enough to be able to record details of craters and mountains, and even then if there is one, but the recording is done the world HST indicates that vary in color, from white, dark orange-brown to dark. The colors are believed due to ultra-violet radiation from the sun which is in the distance, breaking the existing methane on Pluto's surface, causing a dark brown residue rich in carbon.

Pluto is also changing illumination, in the northern polar region of southern luminous and dark and reddish. The summer approaching Pluto's north pole causes ice to melt and experiencing freezing in the darker areas due terbayangi on the planet. HST has shown that Pluto is not just a ball of ice and rock, but a world that has a dramatic change in atmosphere.

Change season due to the elliptical orbit of Pluto 248 years along with the slanted axis. Season becomes elliptical symmetry because Pluto's orbit. Spring transition into summer in the polar hemisphere rapidly occurred in the north, because Pluto is moving very fast along the orbit as it moves around the Sun in the direction of approach.

Earth Observation landing between 1988 and 2002 showed the mass multiplication of the atmosphere have all the time allegedly due to heating and sublimation of nitrogen ice. HST images of the season to give an understanding of what happened on Pluto and the fate of the atmosphere.

HST image of this is that terdetil at the moment, at least until the New Horizon spacecraft will fly past Pluto and will record more detailed images again, and give a better picture of what is happening on the surface of Pluto, and was still waiting until 2015 to will come.

Source: Hubblesite and Langit Selata n

Soal-Soal Latihan Astronomi 2010

2010-01-26T23:33:00.006+07:00

Silakan didownload beberapa file soal-soal latihan yang dapat digunakan sebagai bahan diskusi dan latihan. Selamat belajar dan semoga bermanfaat.

Link:
1. http://astronomy.case.edu/steven/temp/
olympiad/2008_C_olympiad_master.pdf
2. http://olympiads.hbcse.tifr.res.in/uploads/inao-jr-ans
3. Soal - Soal dari Ajang 2nd dan 3rd IOAA

Oposisi Mars 2010

2010-01-24T16:30:00.003+07:00

Beberapa tahun yang lalu, mungkin ada yang masih ingat, ketika ramai dibicarakan bahwa Mars akan mendekati Bumi dengan ukuran sebesar Bulan, tentunya tidak!

Oposisi Mars dilihat dari arah kutub. Kredit : ESA

Memang benar bahwa dalam lintasannya mengitari Matahari, baik Bumi dan Mars pada suatu ketika berada pada suatu posisi yang saling mendekat satu sama lain, karena lintasan Bumi, Mars, tidaklah merupakan lingkaran sempurna, tetapi berupa lintasan elips, dengan Matahari berada pada salah satu titik fokus elips.

Bumi bergerak mengitari Matahari lebih cepat daripada Mars, dan setiap 26 bulan, Bumi akan mendahului Mars melalui lintasan dalam, dan ketika itu, saat Matahar-Bumi-Mars berada pada segaris, dikenal sebagai oposisi Mars. Maka, oposisi Mars akan selalu terjadi setiap 26 bulan, dan biasanya di waktu oposisi tersebut maka, Bumi dan Mars berada pada posisi yang saling berdekatan.

Simulasi posisi Bumi-Mars & Matahari dapat dilihat di sini.

Jarak antara Bumi dan Mars tidak selalu sama setiap oposisi, karena orbit Mars yang sedikit lebih lonjong, maka jarak terdekat antara Bumi dan Mars tidak selalu tepat saat oposisi, tetapi selalu berada di sekitar waktu oposisi, yang berselisih beberapa hari dari waktu oposisinya. Dan biasanya, pada saat saling mendekat itu, maka Mars akan tampak cerlang dan cerlang, lebih kemerahan, kelihatan lebih jelas, baik diamati mempergunakan mata, binokular ataupun teleskop, tetapi yang pasti, tidak akan mencapai sebesar Bulan!

Oleh karena bentuk geometri yang unik itu, maka setiap terjadi jarak yang terdekat antara Bumi-Mars (yang berperiode 26 bulan itu), tidak akan pernah sama dari satu kejadian ke kejadian berikutnya. Pada kejadian oposisi Mars tahun 2003, yang dikenal sebagai peristiwa Mars dalam posisi paling dekat (sedekat-dekatnya) dengan Bumi, jarak yang terhitung sebagai terdekat adalah 55758006 km, dengan diameter tampak sekitar 25″; dan fenomena ini hanya bisa terjadi setiap 60 ribu tahun. Besarkah itu? Bagi yang beruntung mengamati saat itu, Mars masih tetap sama seperti Mars yang telah diamati nenek moyang kita, dengan mata telanjang, masih berupa noktah merah terang di langit. Bahkan dengan teleskop sekalipun, tidak banyak berubah kenampakannya, hanya, detilnya agak lebih tampak sedikit.

Mars jelang oposisi yang dipotret Hubble sejak tahun 1995 - 2007. Kredit : NASA/Hubble

Dan kemudian, di awal tahun 2010 ini, melalui siklus 26-bulan berikutnya (sesudah 2007), maka si merah kembali mendekat dengan Bumi! Di bulan Januari ini, Mars telah mencapai kecerlanganan mencapai sekitar -1 magnitudo, cukup terang teramati di langit sebagai suatu noktah merah yang jelas terlihat mempergunakan mata telanjang. Pada tanggal 27 Januari 2010, posisi terdekatnya mencapai 99 juta km, dengan diameter tampak sekitar 14″, lalu, oposisi Mars tercapai pada tanggal 29 Januari 2010, dengan magnitudo mencapai -1,28. Mars akan berada dalam kondisi yang sangat cerlang dengan magnitudo di sekitar -1, sampai dengan tanggal 14 Februari 2010, dan sesudah itu akan semakin meredup.

Lalu, bagaimana kita menemukan Mars? Mudah, di bulan-bulan ini, ketika sore, carilah ke arah terbit di timur, apabila ada sebuah noktah yang cerlang berwarna kemerahan, besar kemungkinan itulah dia. Apabila kita telah mengetahui tentang rasi-rasi di langit, (mempergunakan peta langit sangat membantu), carilah rasi Cancer, maka disitulah ia berada!

Sumber: Langit Selatan

The Known Universe

2010-01-21T20:56:00.005+07:00

What would it look like to travel across the known universe? To help humanity visualize this, the American Museum of Natural History has produced a modern movie featuring many visual highlights of such a trip. The video starts in Earth's Himalayan Mountains and then dramatically zooms out, showing the orbits of Earth's satellites, the Sun, the Solar System, the extent of humanities first radio signals, the Milky Way Galaxy, galaxies nearby, distant galaxies, and quasars. As the distant surface of the microwave background is finally reached, radiation is depicted that was emitted billions of light years away and less than one million years after the Big Bang. Frequently using the Digital Universe Atlas, every object in the video has been rendered to scale given the best scientific research in 2009, when the video was produced. The film has similarities to the famous Powers of Ten video that has been a favorite of many space enthusiasts for a generation.

Source: APOD

Astronomy Without A Telescope – Getting Orientated

2010-01-18T18:16:00.002+07:00

Artikel berikut mengenai bagaimana memperkenalkan astronomi kepada orang lain yang "buta" astronomi. Sumber: universetoday.

We’ve all been there. You’ve met someone nice – but for some inexplicable reason, they don’t get astronomy. So how do you start gently introducing them to your life’s passion (about astronomy that is) without scaring them away?

First it’s important to recognize that not everyone will be instantly in awe to learn you own a 14-inch Schmidt-Cassegrain with four speed microslew. Weird, but there it is. And it’s going to be a challenge getting that special someone to drive out to a lonely spot in the wilderness for some proper dark sky viewing – and don’t even mention that there’s such a thing as naked eye astronomy.

Start with the Sun – it’s big and it’s obvious and everyone gets that it rises in the east and sets in the west. Well, that of course means that the Earth is actually spinning from west to east. And heck, you’re an astronomer, so you’re bound to know your cardinal directions on familiar ground – so just point. We are spinning that way.

And if you are in the right part of the lunar cycle – you might comment, on one of those romantic moonlit evenings, that last night at this time the Moon was there – and tonight it’s shifted a bit to the east. Don’t dwell on it – just put the idea out there. The next night let them note that – hey, it’s moved even further east! They might even notice that it’s filled out a bit – but this is not the time to introduce them to the word gibbous.

What’s happening is that they are starting to make their own astronomical observations. All you have to do is to find an opportune moment to pull the background together. If the Earth spinning from west to east, that means that from a perspective in space – at least from above the North Pole – it’s spinning anti-clockwise. And the fact that the Moon inches further towards the east day by day means it’s orbiting the Earth anti-clockwise.

Hopefully you’ve captured their interest enough to carry on with the fact that actually all the planets orbit the Sun in that same anticlockwise direction – indeed, even the Sun spins in that same direction, once every 28 days. A quick mention of the theory that the whole solar system formed from a gas cloud that spun down into a disk – and it’s probably time to move on to another conservation topic. This is not the time to introduce them to the conservation of angular momentum. Pace yourself.

From here – a wealth of discussion could arise in the days to come. Your potential new partner might ponder whether all the planets spin in the same direction – to which you can reply well mostly, except for Venus and Uranus – and then you’re away talking about planetary collisions. Or, maybe you’ll be asked whether all the planet’s moons orbit in the same direction – to which you can reply well mostly, but there’s Triton that goes the wrong way around Neptune – probably because it came in from the Kuiper Belt. There’s a Kuiper Belt now?

Sekilas tentang 99942 Apophis

2010-01-14T00:12:00.007+07:00

Mungkin Anda belum pernah mendengar tentang asteroid ini. Mengapa asteroid 99942 Apophis ini menjadi beda dengan asteroid lainnya adalah karena ada probabilitas (kemungkinan) orbit asteroid ini menyilang orbit Bumi yang akan menghasilkan tabrakan (collide). Namun, sebelum kita menjadi panik, perlu diperhatikan tentang kecilnya probabilitas tabrakan dan perhitungan orbit masih penuh ketidakpastian. Perlu diketahui, tidak mudah membuat peta lengkap orbit sebuah benda langit seperti asteroid karena orbit asteroid sangat terpengaruh gaya gravitasi benda2 langit lain yang dilewatinya selama mengorbit. Berikut artikel tentang asteroid ini yang diambil dari wikipedia dan NASA.

99942 Apophis (pronounced /əˈpɒfɪs/, previously known by its provisional designation 2004 MN4) is a near-Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a small probability (up to 2.7%) that it would strike the Earth in 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. However, a possibility remains that during the 2029 close encounter with Earth, Apophis will pass through a gravitational keyhole, a precise region in space no more than about 600 meters across, that would set up a future impact on April 13, 2036. This possibility kept the asteroid at Level 1 on the Torino impact hazard scale until August 2006. It broke the record for the highest level on the Torino Scale, being, for only a short time, a level 4, before it was lowered

Additional observations of the trajectory of Apophis revealed the keyhole will likely be missed. On August 5, 2006 Apophis was lowered to a Level 0 on the Torino Scale. As of October 7, 2009, the impact probability for April 13, 2036, is calculated as 1 in 250,000. An additional impact date in 2037 was also identified; the impact probability for that encounter is calculated as 1 in 12.3 million.

Basic data
Based upon the observed brightness, Apophis' length was estimated at 450 metres (1,500 ft); a more refined estimate based on spectroscopic observations at NASA's Infrared Telescope Facility in Hawaii by Binzel, Rivkin, Bus, and Tokunaga (2005) is 350 metres (1,100 ft).

In October 2005 it was predicted that the asteroid will pass just below the altitude of geosynchronous satellites, which are at 35,786 kilometres (22,236 mi). Such a close approach by an asteroid of this size is expected to occur only every 1,300 years or so. Apophis’ brightness will peak at magnitude 3.3, with a maximum angular speed of 42° per hour. The maximum apparent angular diameter will be ~2 arcseconds, so that it will be barely resolved by telescopes not equipped with adaptive optics.

Close approaches
After the Minor Planet Center confirmed the June discovery of Apophis, an April 13, 2029 close approach was flagged by NASA's automatic Sentry system and NEODyS, a similar automatic program run by the University of Pisa and the University of Valladolid. On that date, it will become as bright as magnitude 3.3 (visible to the naked eye from rural as well as darker suburban areas, visible with binoculars from most locations). This close approach will be visible from Europe, Africa, and western Asia. As a result of its close passage, it will move from the Aten to the Apollo class.

After Sentry and NEODyS announced the possible impact, additional observations decreased the uncertainty in Apophis' trajectory. As they did, the probability of an impact event temporarily climbed, peaking at 2.7% (1 in 37). Combined with its size, this caused Apophis to be assessed at level 4 on the Torino Scale and 1.10 on the Palermo scale, scales scientists use to represent the danger of an asteroid hitting Earth. These are the highest values for which any known object has been rated on either scale.

On Friday, April 13, 2029, Apophis will pass Earth within the orbits of geosynchronous communication satellites. It will return for another close Earth approach in 2036.

Precovery observations from March 15, 2004 were identified on December 27, and an improved orbit was computed.Radar astrometry further refined the orbit. The 2029 pass will actually be much closer than the first predictions, but the uncertainty is such that an impact is ruled out. Similarly, the pass on April 13, 2036 carries little risk of an impact.

2013 refinement
The close approach in 2029 will substantially alter the object's orbit, making predictions uncertain without more data. "If we get radar ranging in 2013 [the next good opportunity], we should be able to predict the location of 2004 MN4 out to at least 2070." said Jon Giorgini of JPL. Apophis will pass within 0.09666 AU (14.4 million km) of the Earth in 2013 allowing astronomers to refine the trajectory for future close passes.

In July 2005, former Apollo astronaut Rusty Schweickart, as chairman of the B612 Foundation, formally asked NASA to investigate the possibility that the asteroid's post-2029 orbit could be in orbital resonance with Earth, which would increase the probability of future impacts. Schweickart asked for an investigation of the necessity of placing a transponder on the asteroid for more accurate tracking of how its orbit is affected by the Yarkovsky effect.

NASA Refines Asteroid Apophis' Path Toward Earth
Using updated information, NASA scientists have recalculated the path of a large asteroid. The refined path indicates a significantly reduced likelihood of a hazardous encounter with Earth in 2036.

The Apophis asteroid is approximately the size of two-and-a-half football fields. The new data were documented by near-Earth object scientists Steve Chesley and Paul Chodas at NASA's Jet Propulsion Laboratory in Pasadena, Calif. They will present their updated findings at a meeting of the American Astronomical Society's Division for Planetary Sciences in Puerto Rico on Oct. 8.

"Apophis has been one of those celestial bodies that has captured the public's interest since it was discovered in 2004," said Chesley. "Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about four-in-a million."

A majority of the data that enabled the updated orbit of Apophis came from observations Dave Tholen and collaborators at the University of Hawaii's Institute for Astronomy in Manoa made. Tholen pored over hundreds of previously unreleased images of the night sky made with the University of Hawaii's 88-inch telescope, located near the summit of Mauna Kea.

Tholen made improved measurements of the asteroid's position in the images, enabling him to provide Chesley and Chodas with new data sets more precise than previous measures for Apophis. Measurements from the Steward Observatory's 90-inch Bok telescope on Kitt Peak in Arizona and the Arecibo Observatory on the island of Puerto Rico also were used in Chesley's calculations.

The information provided a more accurate glimpse of Apophis' orbit well into the latter part of this century. Among the findings is another close encounter by the asteroid with Earth in 2068 with chance of impact currently at approximately three-in-a-million. As with earlier orbital estimates where Earth impacts in 2029 and 2036 could not initially be ruled out due to the need for additional data, it is expected that the 2068 encounter will diminish in probability as more information about Apophis is acquired.

Initially, Apophis was thought to have a 2.7 percent chance of impacting Earth in 2029. Additional observations of the asteriod ruled out any possibility of an impact in 2029. However, the asteroid is expected to make a record-setting -- but harmless -- close approach to Earth on Friday, April 13, 2029, when it comes no closer than 18,300 miles above Earth's surface.

"The refined orbital determination further reinforces that Apophis is an asteroid we can look to as an opportunity for exciting science and not something that should be feared," said Don Yeomans, manager of the Near-Earth Object Program Office at JPL. "The public can follow along as we continue to study Apophis and other near-Earth objects by visiting us on our AsteroidWatch Web site and by following us on the @AsteroidWatch Twitter feed."

The science of predicting asteroid orbits is based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids.

NASA detects and tracks asteroids and comets passing close to Earth using both ground and space-based telescopes. The Near Earth-Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them and plots their orbits to determine if any could be potentially hazardous to our planet.

JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. Cornell University operates the Arecibo Observatory under a cooperative agreement with the National Science Foundation in Arlington, Va.

Possible impact effects
NASA initially estimated the energy that Apophis would have released if it struck Earth as the equivalent of 1,480 megatons of TNT. A later, more refined NASA estimate was 880 megatons. The impacts which created the Barringer Crater or the Tunguska event are estimated to be in the 3–10 megaton range. The 1883 eruption of Krakatoa was the equivalent of roughly 200 megatons.

Path of risk where 99942 Apophis may impact Earth in 2036.

The exact effects of any impact would vary based on the asteroid's composition, and the location and angle of impact. Any impact would be extremely detrimental to an area of thousands of square kilometres, but would be unlikely to have long-lasting global effects, such as the initiation of an impact winter (?).

The B612 Foundation made estimates of Apophis' path if a 2036 Earth impact were to occur as part of an effort to develop viable deflection strategies.The result is a narrow corridor a few miles wide, called the path of risk, and it includes most of southern Russia, across the north Pacific (relatively close to the coastlines of California and Mexico), then right between Nicaragua and Costa Rica, crossing northern Colombia and Venezuela, ending in the Atlantic, just before reaching Africa.Using the computer simulation tool NEOSim, it was estimated that the hypothetical impact of Apophis in countries such as Colombia and Venezuela, which are in the path of risk, would have had more than 10 million casualties.An impact several thousand miles off the West Coast of the US would produce a devastating tsunami.

Gerhana Matahari Cincin 15 Januari 2010

2010-01-13T19:56:00.011+07:00

Hari Jumat, tanggal 15 Januari 2010 akan terjadi fenomena Gerhana Matahari Cincin. Gerhana Matahari pada 15 Januari 2010 merupakan gerhana matahari cincin (annular), yaitu bundaran bulan tidak sepenuhnya menutupi matahari sehingga masih tersisa bagian yang bercahaya, yang mengesankan seperti cincin. Namun dari Indonesia, yang bisa kita amati hanyalah Gerhana Matahari Sebagian (GMS) saja, karena tidak ada daerah di Indonesia yang dilalui oleh jalur totalitasnya, tidak seperti GMC 26 Januari 2009 yang lalu.

Daerah di Indonesia yang dapat menyaksikan gerhana nanti adalah seluruh Sumatra dan Kalimantan, bagian barat pulau Jawa, dan bagian utara pulau Sulawesi. Meskipun begitu, proses GMS akan bisa kita saksikan lebih baik apabila kita berada di wilayah barat Indonesia. Di sana gerhana akan berlangsung lebih lama dan piringan Matahari yang tertutup oleh Bulan juga lebih banyak dibandingkan dengan pengamatan di daerah timur.

Untuk pengamat yang berada di Banda Aceh, gerhana dimulai pada sekitar pukul 13.40 WIB dan berakhir pada pukul 16.40 WIB. Luas daerah piringan Matahari yang tertutupi Bulan mencapai 46% pada saat maksimumnya, yaitu pada sekitar pukul 15.20 WIB. Jumlah tersebut jauh lebih besar daripada hasil pengamatan di Manado yang hanya menutupi 0,3% daerah piringan Matahari saja.

Penjelasan lebih detail tentang Gerhana tersebut disajikan dalam artikel di bawah ini.

The solar eclipse of January 15, 2010 is an annular eclipse of the Sun with a magnitude of 0.9190. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partially obscuring Earth's view of the Sun. An annular solar eclipse occurs when the Moon's apparent diameter is smaller than the Sun, causing the sun to look like an annulus (ring), blocking most of the Sun's light. An annular eclipse will appear as partial eclipse over a region thousands of miles wide.

It will be visible as a partial eclipse in much of Africa, Eastern Europe, Middle East and Asia. It will be seen as annular within a narrow stretch of 300 km (190 mi) width across Central Africa, Maldives, South Kerala, South Tamil Nadu, North Sri Lanka, Burma and China.

Visibility

The eclipse starts at Uganda, passes through Nairobi, enters Indian ocean where the greatest eclipse is taking place in mid of Ocean for a maximum of 11 Mins and 7.7 seconds.

After that enters Maldives, where it would be the longest on land with 10.8 Min of viewing. This makes the tiny islands of Maldives the best spot for viewing this eclipse from land. The annular Eclipse at Male', the capital city of Maldives starts at 12:20:20 hrs and ends 12:30:06 hrs Maldives local time (GMT+5hrs). This is also the longest duration of any city having an international airport in the eclipse track.[1]

After that enters and exits India at Rameswaram. Only place of land under the eclipse on India. At approx 13.20 hrs IST, there is a annular solar Eclipse of sun over India. The eclipse is viewable for full 10.4 min in India. The best place from India is Dhanushkodi in Pamban Island off Tamil Nadu coast. Dhanushkodi is now a ghost town and it is about 18 km South east from Rameshwaram and 18 Km West of Mannar Island in Sri Lanka.

After Rameswaram, enters Sri Lanka at Delft Island, exits at Jaffna in Sri Lanka, cross Bay of Bengal and ends in Burma - China border. Full data is in the NASA website.

For best viewing of the Eclipse, you need to travel to Maldives, where many International flights land and take off everyday, being a world famous tourist destination. Visa for Maldives is free for 30 days for a tourist entry.

The best location In India lies between Kodandaramar Temple islet and Dhanushkodi, which falls on the central line of the Eclipse. The northern most limit of shadow in India is Cuddalore, Neyveli, Erode, Kodaikanal, Madurai. Other best locations: Trivandrum, Thoothukudi and Cape Comorin which lies 22 km north of Central line.

Only means of reaching Dhanushkodi or kodandaramar temple is by ST bus or Auto from Rameswaram and for Dhanushkodi after road's end it is only by fish carts or 4x4 SUVs. Permission is required for entering Dhanushkodi ruins from the coast guard post as that area is 10 km from Sri Lankan coast.

The centre line passes some 2 km east of Kodandaramar Temple. The exact location is between NH end and Dhanushkodi ruins. Dhanushkodi is about 2 km east of the central line. The degree difference is about 0.2 between Central line - Kodandaramar Temple and Dhanushkodi ruins vice versa. Dhanushkodi is about 5 km from Kodandaramar Temple.

Enthusiasm

People, especially the sky enthusiasts from entire India are highly enthusiast about the annular eclipse as the last total solar eclipse of July 22, 2009, being visible on Indian soil remained somewhat a frustrating experience for many of them who got clouded out on the eclipse day in Monsoon cloud. The total solar eclipse of August 11, 1999, was also similar negative experience.

Astronomy clubs from the whole country are gathering in different locations along the shadow track. One section of them, preferring to observe Bailie Beads more are concentrating on the location at the northern limit of the shadow track while the other section is going deep towards the centerline to have better view of the Ring shaped Sun.

Leave aside the sky watcher's associations from Bangalore or Chennai, even clubs like SWAN(Sky Watchers Association of North Bengal) from eastern Himalayan region like Darjeeling or North East region are also gathering in Rameswaram.

Members of SPACE (Science Popularisation Association of Communicators and Educators) and STEPL (Space Technology Education pvt ltd) have planned various observation plans for this eclipse which includes scientific studies as well as watching eclipse for a layman as a curious observer.

Sumber: NASA, wikipedia, duniaastronomi

Sense of Scale: Star's Size

2010-01-12T22:55:00.001+07:00

Sumber: wikipedia

Hujan Meteor Quadrantins - 3/4 Januari 2010

2010-01-04T16:44:00.003+07:00

The Quadrantid meteor shower is one of the strongest meteor showers of the year, but observers can be disappointed if conditions are not just right. The point from where the Quadrantid meteors appear to radiate is located within the extinct constellation Quadrans Muralis. On modern star charts, this radiant is located where the constellations Hercules, Boötes, and Draco meet in the sky. The shower can appear almost nonexistent until about 11 p.m. Unfortunately, the radiant does not attain a very high altitude for most Northern Hemisphere observers before morning twilight puts an end to the show. The best observations are actually possible from countries with high northern latitudes, such as Canada, Finland, Sweden, and Norway. The display is virtually nonexistent for observers in the Southern Hemisphere.

The Quadrantids generally begin on December 28 and end on January 7, with maximum generally occurring during the morning hours of January 3/4. The Quadrantids are barely detectable on the beginning and ending dates, but observers in the Northern Hemisphere can see from 10 to around 60 meteors per hour at maximum. The maximum only lasts for a few hours.

Thus, the Quadrantid meteor shower is an extremely short one, lasting only a few hours. In 2010 the Quadrantids are predicted to reach a peak of about 120 meteors per hour at 1 p.m. EST on Sunday, January 3. Unfortunately, for us in North Carolina, this sharply peaked shower will not really get rolling before sunrise although a few early meteors may be spotted before morning twilight as the shower approaches. Viewers in Asia will fare better since the peak occurs before sunrise there. In any case, one should observe from a clear, dark location with a good horizon. Look high in the northeast for meteors appearing to radiate out of a point between the constellations of Hercules the strong man and Boötes the herdsman. Binoculars or telescopes are not needed to observe meteors. This year Full Moon occurs on New Years Eve which means a waning gibbous moon will interfere with observations of the fainter meteors between midnight and dawn. Incidentally, meteor showers are usually named after the constellation out of which the meteors seem to originate, i.e., their radiant point. However, there is no modern constellation of Quadrans. Instead, this shower retains its name from the obsolete constellation of Quadrans Muralis an instrument used to measure the positions of stars. The actual radiant of the shower is in the edge of Boötes.

(From several sources: 1 dan 2)

Astrofotografi - The Atmosphere and Observing

2009-12-16T22:31:00.002+07:00

Tahukah Anda dengan istilah "seeing" atau sering diterjemahkan dengan istilah penampakan. Istilah ini sering membingungkan orang awam karena kata penampakan sering digunakan untuk konteks lainnya. Dalam astronomi, seeing (atau penampakan) merupakan ukuran baik tidaknya kondisi langit (tepatnya atmosfer) untuk mendapatkan hasil pengamatan yang baik. Seeing yang jelek terjadi jika atmosfer sedang dalam kondisi bergejolak. Hal ini akan membuat bintang nampak berkelap kelip dan akan nampak buram ketika difoto. Tentunya hal ini akan mengganggu pengamatan oleh astronom. Penjelasan lebih lengkapnya diberikan di bawah ini.

Introduction

An observer, be they at a mountain top observatory, or in their own back yard must, at all times contend with the Earth’s atmosphere. It is a notoriously unpredictable and limiting factor in obtaining fine views of the Planets, and close binary stars. Many often comment, especially here in the UK that seeing is all too often mediocre on most nights, but what are the factors that contribute to this?. Are there ways and signs, which indicate whether the atmosphere, will be stable or turbulent on a given night?.

What is Seeing?
So what exactly is atmospheric seeing? - it is high frequency temperature fluctuations of the atmosphere, and the mixing of air “parcels” of different temperatures/densities. This behaviour of the atmosphere is seen at the eyepiece as a blurred, moving, or scintillating image. There are roughly 3 main areas where Atmospheric turbulence occurs. Near ground seeing (0 – 100metres or so.) central troposphere (100m – 2km), and High troposphere (6-12km.) Each area exhibits different characteristics, which are explained in more detail below.

Lower Altitude Effects: The air near the ground is where the great majority of turbulent airflow of the atmosphere occurs, which of course happens to be the area where the great majority of amateur observers are located!. This is caused mainly by areas (houses, other building etc) of varying density radiating heat differently, resulting in local convection currents. This is caused when the Sun heats the ground during the day, and the heat is then radiated away at night. An un-varying topography, such as grassy fields, and large bodies of water are favourable to observe over, at they radiate the stored heat from the day more slowly and equally. Also the telescope itself can perturb the image, if it hasn’t reached ambient temperature, this will result in a “boiling effect” when viewing. One should leave their scope for at least 1 hr prior to observing and probably longer. Also certain types of telescope and observatory are more prone to turbulence. Newtonian reflectors can be troublesome if not properly ventilated, as can Schmidt Cassegrain’s if not left to cool for long enough. As for observatories, Domes have poorer characteristics for stable seeing than run of roof designs.
Mid- Altitude Effects: The turbulence at these altitudes is determined largely by the topography upwind of the observing site. Hence again, living downwind of a large city, or densely populated area, mountain range or other very varied topography will perturb the atmosphere. Downwind of a mountain peak will disrupt the airflow into turbulent eddies, resulting in scintillating images. This effect can prevail as far as 100km downwind of the peak. In this aspect, it is best to observe where the prevailing winds across your site have travelled over an unvarying terrain (large body of water or hills/fields for many miles upwind of the site.) This will help produce a laminar flow, and stable images.
High Altitude Effects: Effects at this altitude are caused by fast moving “rivers” of air know as Jet streams. Wind shears at around the 200-300mb altitude level can cause images to appear stable, but very fuzzy, and devoid of fine detail. There isn’t anything the observer can do to prevent these effects, but forecasts are available, to help predict weather a Jet stream is present over your area. Areas of the Northern hemisphere most affected by the Polar jet stream are the Central US, Canada, North Africa, and Northern Japan. The Jet stream’s position varies with the seasons, tending to move further South during the winter and spring months.

The best locations for good seeing
The world’s finest locations for a stable atmosphere are mountain top observatories, located above frequently occurring temperature inversion layers, where the prevailing winds have crossed many miles of ocean. Sites such as these (La Palma, Tenerife, Hawaii, Paranal etc) frequently enjoy superb seeing much of the year, (with measured turbulence as low as 0.11” arc seconds occurring at times) due to a laminar flow off the ocean. Sea level locations, on shorelines, where the prevailing winds have crossed many miles of ocean (Florida, Caribbean Islands, Canary Islands etc) can be almost as good, and generally very consistent and stable conditions prevail there. Also a major factor is generally unvarying weather patterns, dominated by large anti-cyclones (High pressure systems.) Areas outside these large high-pressure systems have more variable weather, and are more prone to a more variable state of atmospheric stability.

Other, less well know locations where excellent stability prevails are the Island of Madeira’s highest point (Encumeada Alta, 1800m) where seeing is better than 1” arc second 50% of the time. At Mount Maidanak (Uzbekistan, 2600m) the median seeing value observed from 1996-2000 was just 0.69” arc seconds, presenting a site with properties almost as good as Paranal and La Palma.

Figure 01: Above are the observatories (Left) Roque De Los Muchachos on La Palma, and (Right) Observatorio del Teide on Tenerife. Both are located at 2400m above sea level, and are among the worlds finest observing locations. Measured turbulence values at these locations is better than 1” arc second a staggering 80% of the year. (Courtesy ENO.)

Figure 02: Above is a diagram showing how mountains break up stable airflow into turbulence. Note the difference in the probable views from site A (facing into the prevailing winds off the ocean) and site B (Located on the downwind side of the mountain peaks.)

Predicting your local seeing
So is it possible to predict Atmospheric seeing with any accuracy?. The answer to this is yes, most of the time. For example poor seeing will almost always occur after a cold front has passed over, replacing the warmer air, with cooler air, which often gives rise to local convection, and turbulent skies. However, preceding a cold front the air is warmer, and more stable. This is especially true when a large High-pressure system has been present, and mist or fog forms. At these times, transparency can be reduced, but seeing can be excellent. It is also my experience that strong winds are often associated with poor seeing. Another thing to look out for is what type of clouds are present. Lots of cumulus forming in the afternoon due to convection will probably mean seeing will be poor for several hours after sunset. However if the winds are light, and high altitude cirrus shows a smooth linear pattern, this often indicates that the seeing will be good. It was also once thought that maritime locations were far from optimal for good seeing conditions, but as we have seen earlier in the article this is often far from the case.

An even easier way to quickly gauge if a given night will present fine telescopic views is to simply see how much the stars are twinkling. If they twinkle little, and slowly, it probably indicates seeing conditions are reasonably good. However, if they are twinkling madly its probably a sign the views will be poor. This basic method does work quite well, but isn’t 100% accurate. Nights when fast, high altitude turbulence prevails will not show itself as noticeable twinkling, and one must simply look through their telescope to see what’s happening.

Figure 03: Above is a diagram showing a cold front, and associated air masses. The air preceding the front is older, and warmer, and generally quite stable as the ground/air temperature difference is small. However, after the front passes, the warmer air is replaced by cooler air, resulting in significant local convection causing turbulence. Seeing wont improve until the ground/air temperatures again equalize – this usually takes several hours.

A scale of seeing
Many scales have been devised to rate how steady the atmosphere is on a given night. Below is one of the most popular in use, and one I personally use. This scale of seeing is the Pickering Scale, devised by Harvard Observatory's William H. Pickering (1858-1938). Pickering used a 5-inch refractor to devise the scale. His comments about diffraction patterns will have to be modified for larger or smaller instruments. A good starting point:

p1. Star image is usually about twice the diameter of the third diffraction ring if the ring could be seen; star image 13" in diameter.

p2. Image occasionally twice the diameter of the third ring (13").

p3. Image about the same diameter as the third ring (6.7"), and brighter at the centre.

p4. The central Airy diffraction disk often visible; arcs of diffraction rings sometimes seen on brighter stars.

p5. Airy disk always visible; arcs frequently seen on brighter stars.

p6. Airy disk always visible; short arcs constantly seen.

p7. Disk sometimes sharply defined; diffraction rings seen as long arcs or complete circles.

p8. Disk always sharply defined rings seen as long arcs or complete circles, but always in motion.

p9. The inner diffraction ring is stationary. Outer rings momentarily stationary.

p10. The complete diffraction pattern is stationary.

Note: On this scale 1-2 is very poor, 3-4 is poor, 5 is fair, 6-7 is good, 7-8 very good, and 8-10 excellent.

Fig 04. A drawing of Jupiter by the author, simulated to show 3 different views as a high quality 25 cm reflector would show the Planet at powers of 350x. (far left) under excellent seeing, (centre) under fair seeing, and (far right) very poor seeing.

Source: The Atmosphere and Observing by Damien Peach

Universe

2009-12-16T08:34:00.003+07:00

Gerhana Bulan di Malam Tahun Baru

2009-12-15T19:36:00.009+07:00

Malam tanggal 31 Desember 2009, akan dihiasi dengan adanya fenomena Gerhana Bulan Sebagian. Hanya sedikit piringan Bulan akan memasuki umbra Bumi sehingga permukaan Bulan purnama akan nampak sedikit redup dibandingkan biasanya.

Data lengkap tentang Gerhana Bulan tersebut dapat dilihat di bawah ini (klik untuk gambar dengan resolusi yang lebih besar, note: Jam WIB setara dengan UT + 7 jam dan fenomena gerhana dapat teramati baik setelah mulai masuk fasa U1):

Source: NASA dan Wikipedia

Hujan Meteor Geminid di Penghujung Tahun 2009

2009-12-13T12:11:00.001+07:00

Di penghujung tahun 2009, di tengah guyuran hujan yang turun hampir setiap harinya, kita akan mendapat kesempatan untuk menikmati Hujan Meteor Geminid yang merupakan hujan meteor tahunan. Jadi.. siapkan kopi dan coklat panas untuk menemanimu memandangi kilatan meter di malam hari…

Hujan meteor Geminid akan megalami puncaknya pada tanggal 13 – 14 Desember 2009, bertepatan dengan dimulainya Bulan Baru, sehingga ini akan menjadi kesempatan yang baik untuk melakukan pengamatan karena tidak akan ada cahaya bulan. Hujan meteor Geminid akan bisa teramati dari sleuruh wilayah di Indonesia pada tanggal 13 Desember malam menjelang dini hari dan pada tanggal 14 malam menjelang tengah malam. Menurut perkiraan International Meteor Organization, di saat maksimum meteor yang akan terlihat bisa mencapai 100 – 140 meteor per jam, pada tanggal 14 Desember jam 05.10 UT atau jam 12.10 wib.

Hujan meteor Geminid merupakan salah satu hujan meteor yang dinantikan karena intensitasnya yang terus meningkat dalam dekade ini dan diharapkan tren yang sama masih akan diteruskan.

Meteor yang tampak dari rasi Gemini ini berasal dari sisa pecahan obyek yang dikenal sebagai 3200 Phaethon, yang dulunya diperkirakan merupakan asteroid. Saat ini Phaethon sudah menjadi komet yang punah. Jadi sebenarnya, ia adalah kerangka batuan dari komet yang sudah kehilangan es setelah berkali-kali melintas Matahari dari dekat. Nah, Bumi yang melintas dalam aliran puing-puing 3200 Phaethon setiap tahun pada pertengahan Desember akan menyebabkan puing-puing itu terbang dari rasi Gemini/. Tepatnya di dekat bintang terang Castor dan Pollux.

Meteor Geminid pertama kali terlihat pada akhir abad ke-19, tak lama setelah perang sipil di Amerika berakhir. Pada saat pertama muncul, hujan meteornya masih lemah dan tidak terlalu menarik perhatian. Pada saat itu debu yang masuk atmosfer Bumi itu hanya bergerak dengan kecepatan 130000 km/jam. Di masa itu, sama sekali tak nampak kalau hujan meteor ini akan berlangsung setiap tahun. Yang menarik, saat ini hujan meteor Geminid merupakan salah satu hujan meteor yang cukup kuat dan menarik perhatian para pengamat. Bahkan ia semakin kuat dari tahun ke tahun. Hal ini disebabkan oleh gravitasi Jupiter yang berlaku pada aliran puing-puing Phaethon dan menyebabkan mereka bergeser mendekati orbit Bumi. Meteor Geminid sendiri masih tergolong meteor dengan kecepatan menengah pada kisaran 35 km / detik, sehingga akan mudah dikenali di bentangan langit malam.

Jadi, apa yang harus dilakukan untuk mengamati hujan meteor Geminid? Sediakan kopi..atau coklat panas. Keluarlah ke halaman atau area lapang. Bawa peta langit (planisphere/laptop/PDA yang sudah dilengkapi piranti peta langit) untuk dilihat, bawa senter, siapkan ipod, dan mulailah menatap langit ke arah timur laut, dimana rasi Gemini berada. Rasi Gemini akan terbit pada kisaran pukul 21.00 wib, jadi anda bisa keluar rumah mulai jam 21.00 sampai dini hari untuk menikmati hujan meteor Geminid.

Sumber: www.langitselatan.com

Mengenal Objek Langit

2009-12-07T12:15:00.004+07:00

Di bawah ini ditampilkan foto langit dari daerah Himalaya (klik gambar untuk resolusi yang lebih besar). Coba analisa rasi apa yang nampak di sana. Selain itu, ada objek Messier yang muncul pula. Sebutkan apa namanya.

Jawabannya bisa dilihat di sini.

Basic Astronomy: Phases of The Moon

2009-12-06T14:30:00.000+07:00

Moon phases, or lunar phases, refer to the different appearances that the Moon takes on over the course of a lunar month. At the beginning of a lunar month, the Moon is dark. And then, over the course of the month, more and more of the Moon is illuminated until we see a full moon. Then the amount of illuminated moon decreases to a new moon again. Then the cycle starts all over again. These are the phases of the Moon.

When thinking about what causes the phases of the Moon, you've got to realize that the Moon is always half illuminated by the Sun. This is the same for all the objects in the Solar System. We see the different moon phases from here on Earth because our perspective of the Moon changes as it orbits around the Earth. When we can see the Moon fully illuminated, then the Sun and Moon are on opposite sides of the Earth; this is a full moon. The situation is reversed when the Moon and the Sun are on the same side of the Earth. This is when we see a new moon. The other lunar moon phases occur when the Moon makes various angles compared to the Earth.

Eight Phases of the Moon
Although the lunar phases actually transition smoothly from one phase to another, we have developed different terms for the 8 moon phases that look distinct. The Moon's appearance moves through each of these moon phases as the amount of sunlight falling on it changes from our perspective. this is a cycle that always moves in the same direction. The Moon will always go from new moon to first quarter then full moon, then last quarter and back to new moon again.

Here are the eight phases of the moon:

New Moon – When the illuminated side of the Moon is away from the Earth. The Moon and the Sun are lined up on the same side of the Earth, so we can only see the shadowed side. This is also the time that you can experience solar eclipses, when the Moon passes directly in front of the Sun and casts a shadow onto the surface of the Earth. During a new moon, we can also see the reflected light from the Earth, since no sunlight is falling on the Moon – this is known as earthshine.
Crescent – The crescent moon is the first sliver of the Moon that we can see. From the northern hemisphere, the crescent moon has the illuminated edge of the Moon on the right. This situation is reversed for the southern hemisphere.
First Quarter – Although it's called a quarter moon, we actually see this phase when the Moon is half illuminated. This means that the Sun and the Moon make a 90-degree angle compared to the Earth.
Waxing Gibbous – This phase of the Moon occurs when the Moon is more illuminated that half, but it's not yet a full Moon.
Full Moon – This is the phase when the Moon is brightest in the sky. From our perspective here on Earth, the Moon is fully illuminated by the light of the Sun. This is also the time of the lunar month when you can see lunar eclipses – these occur when the Moon passes through the shadow of the Earth.
Waning Gibbous – In this lunar phase, the Moon is less than fully illuminated, but more than half.
Last Quarter – At this point of the lunar cycle, the Moon has reached half illumination. Now it's the left-hand side of the Moon that's illuminated, and the right-hand side in darkness (from a northern hemisphere perspective).
Crescent – This is the final sliver of illuminated moon we can see before the Moon goes into darkness again.

And so, the Moon passes through each of these phases each lunar month. It takes a total of 29.53 days to go from new moon to new moon.

Source: universe today

How Galaxies Lose Their Gas

2009-12-05T14:55:00.000+07:00

As galaxies evolve, many lose their gas. But how they do this is a point of contention. One possibility is that it is used to form stars when the galaxies undergo intense periods of star formation known as starburst. Another is that when large galaxies collide, the stars pass through one another but the gas gets left behind. It's also possible that the gas is pulled out in close passes to other galaxies through tidal forces. Yet another possibility involves a wind blowing the gas out as galaxies plunge through the thin intergalactic medium in clusters through a process known as ram pressure.

A new paper lends fresh evidence to one of these hypotheses. In this paper, astronomers from the University of Arizona were interested in galaxies that displayed long gas tails, much like a comet. Earlier studies had found such galaxies, but it was unclear whether or not this gas tail was pulled out from tidal forces, or pushed out from ram pressure.

To help determine the cause of this the team used new observations from Spitzer to look for subtle differences in the causes of a tail following the galaxy ESO 137-001. In cases where tails are known to be pulled out tidally (such as in the M81/M82 system), there "is no physical reason why the gas would be preferentially stripped over stars." Stars from the galaxy are pulled out as well and often large amounts of new star formation are induced. Meanwhile, ram pressure tails should be largely free of stars although some new star formation may be expected if there is turbulence in the tail which causes regions of higher density (think like the wake of a boat).

Examining the tail spectroscopically, the team was unable to detect the presence of large numbers of stars suggesting tidal processes were not responsible. Furthermore, the disk of the galaxy seemed relatively undisturbed by gravitational interactions. To support this, the team calculated the relative strengths of the forces acting on the galaxy. They found that, between the tidal forces acting on the galaxy from its parent cluster, and its own centripetal forces, the internal forces where greater, which reaffirmed that tidal forces were an unlikely cause for the tail.

But to confirm that ram pressure was truly responsible, the astronomers looked at other parameters. First they estimated the gravitational force for the galaxy. In order to strip the gas, the force generated by the ram pressure would have to exceed the gravitational one. The energy imparted on the gas would then be measurable as a temperature in the gas tail which could be compared to the expected values. When this was observed, they found that the temperature was consistent with what would be necessary for ram stripping.

From this, they also set limits on how long gas could last in such a galaxy. They determined that in such circumstances, the gas would be entirely stripped from a galaxy in ~500 million to 1 billion years. However, because the density of the gas through which the galaxy would slowly become denser as it passed through the more central regions of the cluster, they suggest the timescale would be much simpler. While this timescale say seem long, it is still shorter than the time it takes such galaxies to make a full orbit in their cluster. As such, it is possible that even in one pass, a galaxy may lose its gas.

If the gas loss occurs on such short timescales, this would further predict that tails like the one observed for ESO 137-001 should be rare. The authors note that an “X-ray survey of 25 nearby hot clusters only discovered 2 galaxies with X-ray tails.”

Although this new study in no way rules out other methods of removing a galaxy's gas, this is one of the first galaxies for which the ram stripping method is conclusively demonstrated.

Source: universe today
Original source: A Warm Molecular Hydrogen Tail Due to Ram Pressure Stripping of a Cluster Galaxy

2012 Doomsday Hoax

2009-12-01T12:53:00.007+07:00

Sudahkah Anda menonton film 2012? Film ini mengisahkan tentang bencana besar yang diperkirakan akan terjadi pada tahun tersebut. Namun, tahukah Anda banyak fake science yang dimasukkan dalam film tersebut? Jadi, Anda tidak perlu khawatir dunia akan segera kiamat karena tidak ada alasan dan bukti kuat tentang ramalan semacam itu. Berikut ini akan ditampilkan sebuah artikel dari universe today, yang menuliskan pendapat NASA tentang isu-isu yang tidak benar yang diperkirakan orang (bahkan dengan bodohnya dipercaya orang) akan terjadi di tahun 2012 (khususnya di tanggal 21 Desember 2012).

NASA is now joining in to combat the 2012 nonsense. Don Yeomans, manager of NASA's Near Earth Object office has produced a video and written an article, providing the scientific realities surrounding the celestial happenings of 2012. Yeomans has done a wonderful job explaining everything that is and isn't going to happen in 2012, and we're happy to add his work to our collection of 2012 debunking articles.

The Galileo spacecraft's view of the Moon and Earth On December 16, 1992, 8 days after its encounter with Earth, the Galileo spacecraft looked back from a distance of about 6.2 million kilometers (3.9 million miles) to capture this remarkable view of the Moon in orbit about Earth. Image credit: NASA/JPL There apparently is a great deal of interest in celestial bodies, and their locations and trajectories at the end of the calendar year 2012. Now, I for one love a good book or movie as much as the next guy. But the stuff flying around through cyberspace, TV and the movies is not based on science. There is even a fake NASA news release out there… So here is the scientific reality on the celestial happenings in the year 2012.

Nibiru, a purported large object headed toward Earth, simply put – does not exist. There is no credible evidence – telescopic or otherwise – for this object's existence. There is also no evidence of any kind for its gravitational affects upon bodies in our solar system.

The Mayan calendar does not end in December 2012. Just as the calendar you have on your kitchen wall does not cease to exist after December 31, the Mayan calendar does not cease to exist on December 21, 2012. This date is the end of the Mayan long-count period, but then – just as your calendar begins again on January 1 – another long-count period begins for the Mayan calendar.

There are no credible predictions for worrisome astronomical events in 2012. The activity of the sun is cyclical with a period of roughly 11 years and the time of the next solar maximumis predicted to occur in the period 2010 – 2012. However, the Earth routinely experiences these periods of increased solar activity – for eons (very long period of time -red) – without worrisome effects. The Earth’s magnetic field, which deflects charged particles from the sun, does reverse polarity on time scales of about 400,000 years but there is no evidence that a reversal, which takes thousands of years to occur, will begin in 2012. Even if this several thousand year-long magnetic field reversal were to begin, that would not affect the Earth’s rotation nor would it affect the direction of the Earth’s rotation axis… only Superman can do that.

The only important gravitational tugs experienced by the Earth are due to the moon and sun. There are no planetary alignments in the next few decades, Earth will not cross the galactic plane in 2012, and even if these alignments were to occur, their effects on the Earth would be negligible. Each December the Earth and Sun align with the approximate center of the Milky Way Galaxy but that is an annual event of no consequence.

The predictions of doomsday or dramatic changes on December 21, 2012 are all false. Incorrect doomsday predictions have taken place several times in each of the past several centuries. Readers should bear in mind what Carl Sagan noted several years ago; "extraordinary claims require extraordinary evidence."

For any claims of disaster or dramatic changes in 2012, the burden of proof is on the people making these claims. Where is the science? Where is the evidence? There is none, and all the passionate, persistent and profitable assertions, whether they are made in books, movies, documentaries or over the Internet, cannot change that simple fact. There is no credible evidence for any of the assertions made in support of unusual events taking place in December 2012.

Written by Don Yeomans, NASA senior research scientist

The Extremely Large Telescope

2009-11-25T11:59:00.002+07:00

The European Southern Observatory (ESO) is planning on building a massive telescope in the next decade. The European Extremely Large Telescope (E-ELT) is a 42-meter telescope in its final planning stages. Weighing in at 5,000 tonnes, and made up of 984 individual mirrors, it will be able to image the discs of extrasolar planets and resolve individual stars in galaxies beyond the Local Group! By 2018 ESO hope to be using this gargantuan scope to stare so deep into space that they can actually see the Universe expanding!

The E-ELT is currently scheduled for completion around 2018 and when built it will be four times larger than anything currently looking at the sky in optical wavelengths and 100 times more powerful than the Hubble Space Telescope – despite being a ground-based observatory.

With advanced adaptive optics systems, the E-ELT will use up to 6 laser guide stars to analyse the twinkling caused by the motion of the atmosphere. Computer systems move the 984 individual mirrored panels up to a thousand times a second to cancel out this blurring effect in real time. The result is an image almost as crisp as if the telescope were in space.

This combination of incredible technological power and gigantic size mean that that the E-ELT will be able to not only detect the presence of planets around other stars but also begin to make images of them. It could potentially make a direct image of a Super Earth (a rocky planet just a few times larger than Earth). It would be capable of observing planets around stars within 15-30 light years of the Earth – there are almost 400 stars within that distance!

The E-ELT will be able to resolve stars within distant galaxies and as such begin to understand the history of such galaxies. This method of using the chemical composition, age and mass of stars to unravel the history of the galaxy is sometimes called galactic archaeology and instruments like the E-ELT would lead the way in such research.

Incredibly, by measuring the redshift of distant galaxies over many years with a telescope as sensitive as the E-ELT it should be possible to detect the gradual change in their doppler shift. As such the E-ELT could allow humans to watch the Universe itself expand!

ESO has already spent millions on developing the E-ELT concept. If it is completed as planned then it will eventually cost about €1 billion. The technology required to make the E-ELT happen is being developed right now all over the world – in fact it is creating new technologies, jobs and industry as it goes along. The telescope's enclosure alone presents a huge engineering conundrum – how do you build something the size of modern sports stadium at high altitude and without any existing roads? They will need to keep 5,000 tonnes of metal and glass slewing around smoothly and easily once it's operating – as well as figuring out how to mass-produce more than 1200 1.4m hexagonal mirrors.

The E-ELT has the capacity to transform our view not only of the Universe but of telescopes and the technology to build them as well. It will be a huge leap forward in telescope engineering and for European astronomy it will be a massive 42m jewel in the crown.

Source: universe today

Soal OSN Astronomi 2009 - Essay Teori

2009-11-24T01:33:00.007+07:00

Koordinat Antares adalah α= 16h 29m 24,40s , δ = -26° 25′ 55.0″. Tentukanlah waktu sideris pada saat bintang Antares terbit dan terbenam di Jakarta (φ = -6° 10′ 28″), dan abaikan refraksi oleh atmosfer Bumi.
Untuk menentukan waktu menanam padi pada tahun ini, seorang petani yang berada di kota A (λ = 7h 10m 27s BT dan φ = -6° 49′) menggunakan posisi gugus bintang Pleiades (α = 3h 47m dan δ = 20° 7′) yang diamati pada jam 7 malam waktu lokal. Kebiasaan ini telah dilakukan oleh para petani di pulau Jawa sejak abad ke-17. Pengamatannya dilakukan dengan menggunakan selongsong bambu yang diisi penuh dengan air, dan diarahkan ke gugus bintang Pleiades di arah timur. Volume air yang tumpah akan menandai posisi Pleiades cukup tinggi untuk dimulai musim menanam padi pada tahun tersebut. Jika panjang selongsong bambu adalah 100 cm dan diameternya 10 cm, dan selongsong tersebut diisi air sampai penuh. Kemudian diarahkan ke Pleiades, dan ternyata air yang tumpah sebanyak 0,785 liter. Tentukan kapan waktu pengamatan Pleiades yang dilakukan petani tersebut?
Angin matahari yang isotropik (sama ke segala arah) menyebabkan laju kehilangan massa matahari 3×10^-14 M_Matahari setiap tahunnya.
1. Berapa massa yang di’tangkap’ setiap hari oleh Bumi ketika mengelilingi matahari?
2. Berapa persen pertambahan berat badan kita setiap hari akibat pertambahan massa bumi yang disebabkan oleh angin matahari ini?
Pada saat sebuah bintang masif meledak menjadi sebuah supernova, maka bintang tersebut akan bertambah terang dalam waktu yang singkat dengan luminositasnya 40 milyar kali lebih besar daripada luminositas Matahari. Jika supernova seperti itu tampak di langit seterang Matahari, berapakah jarak supernova tersebut?
Pengamatan pada panjang gelombang radio pada suatu awan gas yang berputar disekeliling sebuah lubang hitam (black hole) yang berada di pusat galaksi X memperlihatkan bahwa radiasi yang berasal dari transisi hidrogen (frekuensi diamnya = 1420 MHz) terdeteksi pada frekuensi 1421,23 MHz.
1. Hitunglah kecepatan awan ini dan apakah awan ini bergerak menuju atau menjauhi kita?
2. Jika awan gas ini berada 0,2 pc dari lubang hitam, dan orbitnya berupa lingkaran, hitunglah massa lubang hitam.

Silakan didiskusikan dengan teman maupun tutor Anda.
Selain itu, bisa dibandingkan pula dengan jawaban versi salah satu peserta peraih medali Emas OSN 2009 kemarin:

Sumber: Astronomy for Dummies by Adicitra

More on Leonid Meteor Shower 2009

2009-11-23T08:11:00.007+07:00

The year 2009 will not see a Leonid storm, but an outburst for sure. There are still some uncertainties regarding the time of maximum of the 1466 trail. For those of you seeking a definitive date and time, it isn't always possible, but we can learn a whole lot about when and where to look.

The Leonid Meteor Shower belongs to the debris shed by comet 55/P Tempel-Tuttle as it passes our Sun in its 33.2 year orbit. Although it was once assumed it would simply be about 33 years between the heaviest "showers," we later came to realize the debris formed a cloud which lagged behind the comet and dispersed irregularly. With each successive pass of Tempel-Tuttle, new filaments of debris are left in space along with the old ones, creating different "streams" the orbiting Earth passes through at varying times, which makes blanket predictions unreliable at best. Each year during November, we pass through the filaments of its debris – both old and new ones – and the chances of impacting a particular stream from any one particular year of Tempel-Tuttle's orbit becomes a matter of mathematical estimates. We know when it passed… We know where it passed. But will we encounter it and to what degree? Traditional dates for the peak of the Leonid meteor shower occur as early as the morning of November 17 and as late as November 19.

So what can we expect this year? According to NASA's 2009 predictions a significant shower is expected this year when Earth crosses the 1466-dust and 1533-dust ejecta of comet 55P/Tempel-Tuttle. According to J. Vaubaillon, the narrow (about 1-hr) shower is expected to peak on November 17, 2009, at 21:43 (1466) and 21:50 (1533) UT, perhaps 0.5 to 1.0 hour later based on a mis-match in 2008, with rates peaking at about ZHR = 115 + 80 = 195/hr (scaled to rates observed in 2008). E. Lyytinen, M. Maslov, D. Moser, and M. Sato all predict similar activity from both trails, combining to about ZHR = 150 – 300 /hr. P. Jenniskens notes that if the calculated trail pattern is slightly shifted in the same manner as observed before, then the 1533-dust trail would move in Earth's path and its rates would be higher (the 1466-dust trail would move away). However, the 1533-dust trail is distorted in the models, and because of that it is not clear how much higher that would be. This remains a rare opportunity to study old dust trails from comet 55P/Tempel-Tuttle. In such old trails, the model of Lyytinen and Nissinen predicts wide trails, which can be tested by measuring the width of the outburst profile.
Let's take a closer look at the at how the two centuries old trails will affect our observing, beginning with the one created in the year 1466. The exact same trail will be encountered again this year with its maximum rate of up to 115 meteors per hour occurring at 21:43 UT (may be 0.5-1hr later). "The trail will be much closer to the Earth, explaining why we expect a quite high zenith hourly rate." say J. Vaubaillon (et al), "However the discrepancy between the expected time of maximum remains, as well as a general higher expected ZHR. Among the possible explanations are: sensitivity to initial conditions (given that the trail is 16 Rev. old) or change of cometary activity (impossible to verify unfortunately)."
But don't count on only this single trail, because the year 1533 trail will encounter the Earth at almost the same time as the 1466 trail. Its maximum time of arrival is expected to be at 21:50 UT on the 17th of November, with a zenith hourly rate of 80 – for a combined rate of perhaps 200 meteors per hour. "The total level of the shower (ZHR~200/hr) was callibrated using the 2008 observations of the 1466 trail, but nothing is known from the 1533 trail. As a consequence, it will be very interesting to check." comments Vaubaillon, "In particular there might be a difference of up to 1 hour between the 1466 and 1533 trail, or they might even be late together, giving us some insight about how well/poorly we know comet 55P's orbit."

Let's take a closer look with 3D-view of the two trails may have evolved between 1466 and 2009.

Dr. Vaubaillon's colleagues from MSFC (D. Moser and B. Cooke) pointed out that the best location to view the outburst caused by the 1466 and 1533 trails will be centered around India and includes: Nepal, Thailand, Western China, Tadjikistan, Afghanistan, Eastern Iran, South Central Russia, etc. Dr. P. Atreya (IMCCE), citizen of Nepal, is currently organizing an international Leonid observation campaign in his home country. This campaign will involve many amateurs and researchers from Nepal and other countries. The climate conditions in Nepal at this time of the year makes it an excellent spot.

We may never know precisely where and when the Leonids might strike, but we do know that a good time to look for this activity is well before dawn on November 17, 18 and 19. Where do you look? For most of us, the best position will be to face east and look overhead.

Source: Universe today

A trivia question:
Can you calculate how thick the meteor cloud based on information given?

Leonid Meteor Shower 2009

2009-11-19T06:06:00.006+07:00

Bagi Anda yang tidak sempat menyaksikan Leonid Meteor Shower kemarin, silakan saksikan beberapa video yang berkaitan berikut ini.

The Leonid shower is made of bits of debris from the Tempel-Tuttle comet, which streaks through Earth's inner solar system every 33 years.

It leaves a stream of debris in its wake. Forecasters, however, say it's hard to know exactly how many of the meteors will be visible.

This year's Leonid meteor shower will peak early Tuesday, forecasters say, producing mild but pretty sparks over the United States and a more intense outburst over Asia.

Time lapse sequence between the hours of 4:30 UT and 13:30 UT November 17 (10:30PM-7:30AM CST in Manitoba, Canada) looking towards the zenith in a suburban back yard. There are few meteors visible. Most of the streaks in this movie sequence are airplanes.

Source: youtube

Black Dwarf

2009-11-13T08:37:00.004+07:00

A black dwarf is a white dwarf that has cooled down to the temperature of the cosmic microwave background, and so is invisible. A white dwarf is what remains of a main sequence star of low or medium mass (below approximately 9 to 10 solar masses), after it has either expelled or fused all the elements which it has sufficient temperature to fuse. Unlike red dwarfs, brown dwarfs, and white dwarfs, black dwarfs are entirely hypothetical.

Once a star has evolved to become a white dwarf, it no longer has an internal source of heat, and is shining only because it is still hot. Like something taken from the oven, left alone a white dwarf will cool down until it is the same temperature as its surroundings. Unlike tonight's dinner, which cools by convection, conduction, and radiation, a white dwarf cools only by radiation.

Because it's electron degeneracy pressure that stops it from collapsing to become a black hole, a white dwarf is a fantastic conductor of heat (in fact, the physics of Fermi gasses explains the conductivity of both white dwarfs and metals!). How fast a white dwarf cools is thus easy to work out … it depends on only its initial temperature, mass, and composition (most are carbon plus oxygen; some maybe predominantly oxygen, neon and magnesium; others helium). Oh, and as at least part of the core of a white dwarf may crystallize, the cooling curve will have a bit of a bump around then.

The universe is only 13.7 billion years old, so even a white dwarf formed 13 billion years ago (unlikely; the stars which become white dwarfs take a billion years, or so, to do so) it would still have a temperature of a few thousand degrees. The coolest white dwarf observed to date has a temperature of a little less than 3,000 K. A long way to go before it becomes a black dwarf.

Working out how long it would take for a white dwarf to cool to the temperature of the CMB is actually quite tricky. Why? Because there are lots of interesting effects that may be important, effects we cannot model yet. For example, a white dwarf will contain some dark matter, and at least some of that may decay, over timespans of quadrillions of years, generating heat. Perhaps diamonds are not forever (protons too may decay); more heat. And the CMB is getting cooler all the time too, as the universe continues to expand.

Anyway, if we say, arbitrarily, that at 5 K a white dwarf becomes a black dwarf, then it'll take at least 10^15 years for one to form.

However, if weakly interacting massive particles exist, it is possible that interactions with these particles will keep some white dwarfs much warmer than this for approximately 10^25 years. If protons are not stable, white dwarfs will also be kept warm by energy released from proton decay. For a hypothetical proton lifetime of 10^37 years, Adams and Laughlin calculate that proton decay will raise the effective surface temperature of an old one-solar mass white dwarf to approximately 0.06 K. Although cold, this is thought to be hotter than the temperature that the cosmic background radiation will have 10^37 years in the future

One more thing: no white dwarf is totally alone; some have binary companions, others may wander through a dust cloud … the infalling mass generates heat too, and if enough hydrogen builds up on the surface, it may go off like a hydrogen bomb (that's what novae are!), warming the white dwarf quite a bit.

If black dwarfs were to exist, they would be extremely difficult to detect, since, by definition, they would emit very little radiation. One theory is that they might be detectable through their gravitational influence.

Source: universetoday and wikipedia

Sun's Lithium Mistery

2009-11-12T07:59:00.001+07:00

For decades, astronomers have known our Sun contains a low amount of lithium, while other solar-like stars actually have more. But they didn't know why. By looking at stars similar to the Sun to study this anomaly, scientists have now discovered of a trend: the majority of stars hosting planets possess less than 1% of the amount of lithium shown by most of the other stars. “The explanation of this 60 year-long puzzle is for us rather simple,” said Garik Israelian, lead author on a paper appearing in this week's edition of Nature. “The Sun lacks lithium because it has planets.”

This finding sheds light not only on the lack of lithium in our star, but also provides astronomers with a very efficient way of finding stars with planetary systems.

Isrealian and his team took a census of 500 stars, 70 of which are known to host planets, and in particular looked at Sun-like stars, almost a quarter of the whole sample. Using ESO’s HARPS spectrograph, a team of astronomers has found that Sun-like stars that host planets have destroyed their lithium much more efficiently than “planet-free” stars.

“For almost 10 years we have tried to find out what distinguishes stars with planetary systems from their barren cousins,” Israelian said. "We now have found that the amount of lithium in Sun-like stars depends on whether or not they have planets.”

These stars have been "very efficient at destroying the lithium they inherited at birth,” said team member Nuno Santos. “Using our unique, large sample, we can also prove that the reason for this lithium reduction is not related to any other property of the star, such as its age.”

Unlike most other elements lighter than iron, the light nuclei of lithium, beryllium and boron are not produced in significant amounts in stars. Instead, it is thought that lithium, composed of just three protons and four neutrons, was mainly produced just after the Big Bang, 13.7 billion years ago. Most stars will thus have the same amount of lithium, unless this element has been destroyed inside the star.

This result also provides the astronomers with a new, cost-effective way to search for planetary systems: by checking the amount of lithium present in a star astronomers can decide which stars are worthy of further significant observing efforts.

Now that a link between the presence of planets and curiously low levels of lithium has been established, the physical mechanism behind it has to be investigated. “There are several ways in which a planet can disturb the internal motions of matter in its host star, thereby rearrange the distribution of the various chemical elements and possibly cause the destruction of lithium," said co-author Michael Mayor. " It is now up to the theoreticians to figure out which one is the most likely to happen.”

Source: Universetoday

Soal-soal Latihan

2009-10-30T10:15:00.001+07:00

Beberapa soal astronomi sebagai bahan latihan dan diskusi dengan teman2:

If the Earth rotated in the opposite sense (clockwise rather than counterclockwise), how long would the solar day be?
Suppose that the Earth’s pole was perpendicular to its orbit. How would the azimuth of sunrise vary throughout the year? How would the length of day and night vary throughout the year at the equator? at the North and South Poles? where you live?
You are an astronaut on the moon. You look up, and see the Earth in its full phase and on the meridian. What lunar phase do people on Earth observe? What if you saw a first quarter Earth? new Earth? third quarter Earth? Draw a picture showing the geometry.
If a planet always keeps the same side towards the Sun, how many sidereal days are in a year on that planet?
If on a given day, the night is 24 hours long at the North Pole, how long is the night at the South Pole?
On what day of the year are the nights longest at the equator?
From the fact that the Moon takes 29.5 days to complete a full cycle of phases, show that it rises an average of 48 minutes later each night.
What is the ratio of the flux hitting the Moon during the first quarter phase to the flux hitting the Moon near the full phase?
Titan and the Moon have similar escape velocities. Why does Titan have an atmosphere, but the Moon does not?

Selamat belajar

Astronomers Found The Most Distant Cosmic Object

2009-10-30T10:10:00.002+07:00

The redness of the afterglow is indicative of the event's distance

Astronomers have confirmed that an exploding star spotted by Nasa's Swift satellite is the most distant cosmic object to be detected by telescopes.

In the journal Nature, two teams of astronomers report their observations of a gamma-ray burst from a star that died 13.1 billion light-years away.

The massive star died about 630 million years after the Big Bang.

UK astronomer Nial Tanvir described the observation as "a step back in cosmic time".

Professor Tanvir led an international team studying the afterglow of the explosion, using the United Kingdom Infrared Telescope (UKIRT) in Hawaii.

Swift detects around 100 gamma ray bursts every year

He told BBC News that his team was able to observe the afterglow for 10 days, while the gamma ray burst itself lasted around 12 seconds.

The event, dubbed GRB 090423, is an example of one of the most violent explosions in the Universe.

It is thought to have been associated with the cataclysmic death of a massive star - triggered by the centre of the star collapsing to form a "stellar-sized" black hole.

"Swift detects something like 100 gamma ray bursts per year," said Professor Tanvir. "And we follow up on lots of them in the hope that eventually we will get one like this one - something really very distant."

Another team, led by Italian astronomer Ruben Salvaterra studied the afterglow independently with the National Galileo Telescope in La Palma.

Little red dot

He told BBC News: "This kind of observation is quite difficult, so having two groups have the same result with two different instruments makes this much more robust."

"It is not surprising - we expected to see an event this distant eventually," said Professor Salvaterra.

"But to be there when it happens is quite amazing - definitely something to tell the grandchildren."

A GAMMA-RAY BURST RECIPE

Models assume GRBs arise when giant stars burn out and collapse

During collapse, super-fast jets of matter burst out from the stars

Collisions occur with gas already shed by the dying behemoths

The interaction generates the energetic signals detected by Swift

Remnants of the huge stars end their days as black holes

The astronomers were able to calculate the vast distance using a phenomenon known as "red shift".

Most of the light from the explosion was absorbed by intergalactic hydrogen gas. As that light travelled towards Earth, the expansion of the Universe "stretches" its wavelength, causing it to become redder.

"The greater that amount of movement [or stretching], the greater the distance." he said.

The image of this gamma ray burst was produced by combining several infrared images.

"So in this case, it's the redness of the dot that indicates that it is very distant," Professor Tanvir explained.

Before this record-breaking event, the furthest object observed from Earth was a gamma ray burst 12.9 billion light-years away.

"This is quite a big step back to the era when the first stars formed in the Universe," said Professor Tanvir.

"Not too long ago we had no idea where the first galaxies came from, so astronomers think this is a profound moment.

"This is... the last blank bit of the map of the Universe - the time between the Big Bang and the formation of these early galaxies."

Data from two powerful telescopes confirmed the result

And this is not the end of the story.

Bing Zhang, an astronomer from the University of Nevada, who was not involved in this study, wrote an article in Nature, explaining its significance.

The discovery, he said, opened up the exciting possibility of studying the "dark ages" of the Universe with gamma ray bursts.

And Professor Tanvir is already planning follow-up studies "looking for the galaxy this exploding star occurred in."

Next year, he and his team will be using the Hubble Space Telescope to try to locate that distant, very early galaxy.

Source: BBC News

James Webb Space Telescope

2009-09-04T06:07:00.008+07:00

The James Webb Space Telescope (JWST) is a planned infrared space observatory, the partial successor to the aging Hubble Space Telescope. The JWST will not be a complete successor, because it will not be sensitive to all of the light wavelengths that Hubble can see. The main scientific goal is to observe the most distant objects in the universe, those beyond the reach of either ground based instruments or the Hubble. The JWST project is a NASA-led international collaboration with contributors in fifteen nations, the European Space Agency and the Canadian Space Agency.

Current plans call for the telescope to be launched on an Ariane 5 rocket in June 2014, on a five-year mission (10 year goal). The JWST will reside in solar orbit near the Sun-Earth L2 point, which is on a line passing from the Sun to the Earth, but about 1.5 million km farther away from the Sun than is the Earth. This position, which moves around the Sun in exact orbital synchrony with the Earth, will allow JWST to shield itself from infrared from both Sun and Earth, by using a single radiation shield positioned between the telescope and the Sun-Earth direction.

Orbit
To avoid swamping the very faint astronomical signals with radiation from the telescope, the telescope and its instruments must be very cold. Therefore, JWST has a large shield that blocks the light from the Sun, Earth, and Moon, which otherwise would heat up the telescope, and interfere with the observations. To have this work, JWST must be in an orbit where all three of these objects are in about the same direction. The answer was to put JWST in an orbit around the Earth-Sun L2 point.

The L2 orbit is an elliptical orbit about the semi-stable second Lagrange point. The Earth-Sun L2 point, about which the Webb telescope will orbit, is 1.51 million km from the Earth, which is about 3.92 times farther away from Earth than is the moon. This distance underscores how much more difficult the Webb telescope would be to service, after launch.

In the case of JWST, the three bodies involved are the Sun, the Earth and the JWST. Normally, an object circling the Sun further out than the Earth would take more than one year to complete its orbit. However, the balance of gravitational pull at the L2 point (in particular, the extra pull from Earth as well as the Sun) means that JWST will keep up with the Earth as it goes around the Sun. The combined gravitational forces of the Sun and the Earth can hold a spacecraft at this point, so that in theory it takes no rocket thrust to keep a spacecraft in orbit around L2.

Optics
Although JWST has a planned mass half that of the Hubble, its primary mirror (a 6.5 meter diameter gold-coated beryllium reflector) has a collecting area which is almost six times larger. As this diameter is much larger than any current launch vehicle, the mirror is composed of 18 hexagonal segments, which will unfold after the telescope is launched. These mirrors are currently being developed by Axsys Technologies in Cullman, Alabama. Sensitive micromotors and a wavefront sensor will position the mirror segments in the correct location, but subsequent to this initial configuration they will only rarely be moved; this process is therefore much like an initial calibration, unlike terrestrial telescopes like the Keck which continually adjust their mirror segments using active optics to overcome the effects of gravitational and wind loading.

Source : universe today and wikipedia

Astronomers Find Most Distant Supermassive Black Hole Yet

2009-09-03T10:46:00.002+07:00

Astronom dari Universitas Hawaii telah berhasil mengamati sebuah galaksi raksasa yang mengelilingi sebuah supermasif black hole terjauh. Galaksi tersebut berjarak 12,8 milyar tahun , nampak sebesar galaksi Bimasakti dan memiliki sebuah supermasif black hole yang mengandung sedikitnya 1 milyar kali massa dibandingkan massa Matahari.

Pengetahuan tentang galaksi induk dari sang supermasif black hole sangat penting untuk memahami misteri bagaimana galaksi dan black hole telah berevolusi bersama. Hingga saat ini, proses pembelajaran galaksi induk dari alam semesta yang jauh sangat sulit akibat sinarnya terhalang oleh black hole.

Asal muasal dari supermsif black hole masih merupakan masalah yang belum terpecahkan dan penemuan baru ini dapat membuka jalan baru untuk menginvestigasi evolusi bersama galaksi-black hole pada awal terbentuknya alam semesta.

Model yang disukai saat ini membutuhkan beberapa black hole berukuran sedang untuk bergabung. Galaksi induk yang ditemukan dalam penelitian ini menyediakan sumber black hole berukuran sedang tersebut. Setelah membentuk supermasif black hole, black hole ini akan terus berkembang karena kemampuan gravitasinya untuk menarik massa dari objek di sekelilingnya. ENergi yang dilepaskan dalam proses ini berkontribusi atas munculnya sinar terang yang diemisikan dari daerah di sekeliling black hole.

Artikel dari peneliti dapat di-download di sini

Sumber: Universe today

Mars, methane and mysteries

2009-08-18T13:30:00.003+07:00

Mars may not be as dormant as scientists once thought. The 2004 discovery of methane means that either there is life on Mars, or that volcanic activity continues to generate heat below the martian surface. ESA plans to find out which it is. Either outcome is big news for a planet once thought to be biologically and geologically inactive.

The methane mystery started soon after December 2003, when ESA’s Mars Express arrived in orbit around the red planet. As the Planetary Fourier Spectrometer (PFS) began taking data, Vittorio Formisano, Istituto di Fisica dello Spazio Interplanetario CNR, Rome, and the rest of the instrument team saw a puzzling signal. As well as the atmospheric gases they were anticipating, such as carbon monoxide and water vapour, they also saw methane.

“Methane was a surprise, we were not expecting that,” says Agustin Chicarro, ESA Mars Lead Scientist. The reason is that on Earth much of the methane in our atmosphere is released by evolved life forms, such as cattle digesting food. While there are ways to produce methane without life, such as by volcanic activity, it is the possible biological route that has focused attention on the discovery.

The Mars Express detection of methane is not an isolated case. While the spacecraft was en route, two independent teams of astronomers using ground-based telescopes started to see traces of methane. After five years of intensive study, the suite of observations all confirmed the discovery and presented planetary scientists with a big puzzle.

Methane is thought to be stable in the martian atmosphere for around 300 years. So, whatever is generating the methane up there, it is a recent occurrence. In January 2009, a team led by Michael Mumma of NASA’s Goddard Space Flight Center published results that the methane they saw in 2003 was concentrated in three regions of the planet. This showed that the methane was being released at the present time and was being observed before it had time to distribute itself around the planet.

Things then took a strange turn. Instead of taking 300 years to disappear, the methane had almost entirely vanished by early 2006. Clearly something unusual is going on at Mars. “We thought we understood how methane behaved on Mars but if the measurements are correct then we must be missing something big,” says Franck Lefèvre, Université Pierre et Marie Curie, CNRS, Paris and a member of Mars Express’s SPICAM instrument team.

Together with his colleague François Forget, Mars Express Interdisciplinary Scientist in charge of atmospheric studies and also of Université Pierre et Marie Curie, CNRS, Paris, Lefèvre has investigated the disappearance using a computer model of Mars’ climate. “We have tackled the problem as atmospheric physicists, without worrying about the nature of the source of the methane,” he says.

In results published last week they found that, while their computer model can reproduce atmospheric species such as carbon monoxide and ozone, it is unable to reproduce the behaviour of the methane. “Something is removing the methane from the atmosphere 600 times faster than the models can account for,” says Lefèvre. “Consequently, the source must be 600 times more intense than originally assumed, which is considerable even by Earth’s geological standards.”

To remove methane at such a rate, suspicion falls on the surface of the planet. Either the methane is being trapped in the dust there or highly reactive chemicals such as hydrogen peroxide are destroying it, as was hinted by the Viking missions in the 1970s. If the latter, then the surface is much more hostile to organic molecules (those containing carbon) than previously thought. This will make searching for traces of past or present life much tougher and future rovers will have to drill below the martian surface to look for signs of life.

To help get to the bottom of the methane mystery, ESA and the Italian space agency (ASI) are to hold a three-day international workshop in November. The assembled scientists will discuss the results and plan strategies for the future study of methane. At the workshop, the Mars Express PFS team hopes to present a global map of martian methane. “We have made the PFS mapping a priority over the last few months,” says Olivier Witasse, ESA Project Scientist for Mars Express.

In July, ESA agreed with NASA to launch joint missions to Mars. The topic of methane is of such importance that it will be most likely addressed in these future missions. “Understanding the methane on Mars is one of our top priorities,” says Witasse.

However the methane is eventually explained, it makes Mars a more fascinating place than even planetary scientists dreamed.

Source: ESA

Astronomer Found Planetary Nebula Around Heavy Stars

2009-08-16T13:25:00.001+07:00

Lead image caption: An optical image from the 0.6-m University of Michigan/CTIO Curtis Schmidt telescope of the brightest Radio Planetary Nebula in the Small Magellanic Cloud, JD 04. The inset box shows a portion of this image overlaid with radio contours from the Australia Telescope Compact Array. The planetary nebula is a glowing record of the final death throes of the star. (Optical images are courtesy of the Magellanic Cloud Emission Line Survey (MCELS) team).

Planetary nebula – the glowing gaseous shells thrown off by stars during the latter stages of their evolution – were thought to only form around stars the size of our Sun or smaller. Although astronomers had predicted these shells should form around "heavier" stars, none had ever been detected. Until now. An international team of scientists have discovered a new class of object which they call “Super Planetary Nebulae,” found around stars up to 8 times the mass of the Sun.

“This came as a shock to us,” said Miroslav Filipovic from the University of Western Sydney “as no one expected to detect these object at radio wavelengths and with the present generation of radio telescopes. We have been holding up our findings for some 3 years until we were 100% sure that they are indeed Planetary Nebulae”.

The team surveyed the Magellanic Clouds, the two companion galaxies to the Milky Way, with radio telescopes of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia Telescope National Facility. They noticed that 15 radio objects in the Clouds match with well known planetary nebulae observed by optical telescopes.

The new class of objects are unusually strong radio sources and are associated with larger original stars (progenitors), up to 8 times the mass of the Sun. The nebular material around each star may have as much as 2.6 times the mass of the Sun.

Filipovic's team argues that the detections of these new objects may help to solve the so called “missing mass problem” – the absence of planetary nebulae around central stars that were originally 1 to 8 times the mass of the Sun. Up to now most known planetary nebulae have central stars and surrounding nebulae with respectively only about 0.6 and 0.3 times the mass of the Sun but none have been detected around more massive stars.

Some of the 15 newly discovered planetary nebulae in the Magellanic Clouds are 3 times more luminous than any of their Milky Way cousins. But to see them in greater detail astronomers will need the power of a coming radio telescope – the Square Kilometre Array planned for the deserts of Western Australia.

Source: Universetoday

Hubble Ultra Deep Field in 3-D

2009-08-13T06:18:00.008+07:00

Pernahkan Anda mendengar tentang Hubble Ultra Deep Field Image? Jika belum, silakan simak sedikit penjelasan dari wikipedia.

The Hubble Ultra Deep Field, or HUDF, is an image of a small region of space in the constellation Fornax, composited from Hubble Space Telescope data accumulated over a period from September 24, 2003 through January 16, 2004. It is the deepest image of the universe ever taken, looking back approximately 13 billion years, and it will be used to search for galaxies that existed between 400 and 800 million years after the Big Bang.The HUDF image was taken in a section of the sky with a low density of bright stars in the near-field, allowing much better viewing of dimmer, more distant objects. The image contains an estimated 10,000 galaxies.

Located southwest of Orion in the Southern-Hemisphere constellation Fornax, the image covers 11.0 square arcminutes. This is just one-tenth the diameter of the full moon as viewed from Earth, smaller than a 1 mm by 1 mm square of paper held 1 meter away, and equal to roughly one thirteen-millionth of the total area of the sky. The image is oriented such that the upper left corner points toward north (-46.4°) on the celestial sphere.

Contents
The HUDF is the deepest image of the universe ever taken and it will be used to search for galaxies that existed between 400 and 800 million years after the Big Bang (redshifts between 7 and 12). The star near the center of the field is USNO-A2.0 0600-01400432 with apparent magnitude of 18.95.

The field imaged by the ACS contains over 10,000 objects, the majority of which are galaxies, many at redshifts greater than 3, and some that probably have redshifts between 6 and 7. The NICMOS measurements may have discovered galaxies at redshifts up to 12.

Scientific results

High rates of star formation during the very early stages of galaxy formation, under a billion years after the Big Bang.
Improved characterization of the distribution of galaxies, their numbers, sizes and luminosities at different epochs, allowing investigation into the evolution of galaxies.
Confirmation that galaxies at high redshifts are smaller and less symmetrical than ones at lower redshifts, showing the rapid evolution of galaxies in the first couple of billion years after the Big Bang.

(untuk informasi lebih lengkap tentang HUDF, silakan lihat di artikel ini dan untuk peta dari HUDF, silakan klik link ini.)

Berikut juga ditampilkan sebuah video untuk visualisasi HUDF.

Semoga bermanfaat.

Soal Latihan Astrofisika

2009-06-17T11:41:00.000+07:00

Selamat mencoba beberapa soal yang dapat Anda download lewat link berikut:

Soal Latihan Astrofisika - 15 Juni 2009

Selamat belajar.

First Extra-Galactic Planet Spotted in Andromeda

2009-06-15T11:45:00.003+07:00

A star in the Andromeda galaxy has a "companion" with six times the mass of Jupiter.

There's no end to the ingenuity of these astronomers.

We've now spotted some 300 extra-solar planets, with rate of discovery increasing at an extraordinary rate. Astronomers have only seen one of these planets directly; the rest have all been inferred because of the effect that they have on their parent stars: changing their brightness or making them wobble. Of course, you have to be able to see the stars to do this kind of work, so astronomers can only see extra-solar planets in our local region of the Milky Way.

Until now. Gabriele Ingrosso at the National Institute of Nuclear Physics, in Italy, and pals say that there is a way to spot planets in other galaxies. The trick is to exploit a phenomenon called microlensing in which the gravity of one star focuses the light from a more distant one toward Earth.

The advantage of microlensing is that it works best for more distant objects, so it's ideal for planet hunting in other galaxies. In theory, it should be possible to see Earth-size objects in this way. The disadvantage is that microlensing is a relatively rapid, one-off event that lasts a few days at most. That makes observations difficult to verify.

It's hard to see individual stars like this, let alone planets. Astronomers have so far spotted only about a dozen stars in Andromeda in this way, and plans are afoot to search for lots more.

But get this: the light from one of these Andromedan stars showed a distinct variability that the discoverers attribute to an orbiting companion.

And today, a new analysis from Ingrosso and co shows that this companion has a mass about six times that of Jupiter. That's heading into brown-dwarf territory, but it's also well within planetary territory too.

Which means that we may well have seen our first extra-galactic planet.

Source : Tecnology Review

Original reference : Pixel-lensing as a way to detect extrasolar planets in M31.

Soal-soal Latihan

2009-06-15T11:30:00.003+07:00

Berikut ini ditampilkan beberapa soal "kelas berat". Silakan dicoba dan didiskusikan dengan teman atau guru di sekolah Anda.

Having observed the sunrise every day in the same location, the astronomer noticed that the azimuth of the sunrise point changes in the range of 90° during the year. Please find the latitude of the observation place. The refraction and solar disk size can be neglected.
Two stars have the same physical parameters. They are observed close to each other in the sky, but their distances are different. Both stars and the observer are situated inside the uniform cloud of interstellar dust. The photometric measurements of these stars in B band gave the results 11m and 17m, in V band the results were 10m and 15m. What is the ratio of distances to these stars? Assume that the extinction property of interstellar dust is proportional to the wavelength in the degree of (–1.3).
The magnitude of total umbral lunar eclipse is equal to 1.865. Please find the duration of totality. The expansion of the umbra caused by atmosphere can be disregarded
The radius of the Galaxy is equal to 15 kpc, the thickness of its disk being many times less. The mass of the galaxy is equal to 1011 solar masses and it is distributed uniformly in the volume of the galaxy. Two stars are rotating around the center of the galaxy in the same direction by the circular orbits with radii equal to 5 kpc and 10 kpc. Please find the synodic period of the first star while observing from the vicinity of the second star.
The white dwarf with radius 6000 km, surface temperature 10000 K and mass equal to solar one moves through the interstellar cluster of comet cores, each one has radius 1 km and density 1 g/cm3. How many comets must fall on the white dwarf every day to increase its luminosity in two times?

Selamat belajar

Resensi Buku : Menjelajah Tata Surya

2009-05-30T20:21:00.005+07:00

Format: Paperback, 302 halaman
Penerbit: Kanisius
Pengarang: A. Gunawan Admiranto
Harga : Rp.60.000,00
isbn: 9789792119
Tanggal Publish: 31 Mar 2009

Alam semesta telah sejak lama memukau manusia dengan keindahannya dan juga misteri di dalamnya. Dan perjalanan sejarah manusia membuktikan kalau keingintahuan untuk menyingkap misteri di alam semesta telah membawa manusia dalam perjalanan panjang penelitian dan penjelajahan untuk mengungkap satu demi satu misteri yang menyelimuti alam maha luas.

Dari penglihatan akan gerak benda langit dari Bumi sampai penjelajahan telah dilakukan oleh manusia demi menyingkap misteri itu. Buku karangan Gunawan Admiranto, :Menjelajah Tata Surya”, mencoba membawa kita mengenal ruang lingkup Tata Surya dimulai dari sejarah perkembangan konsep Tata Surya sampai dengan anggota keluarga yang ada di tepian luar Tata Surya.

Perjalanan di tata Surya diawali dari Matahari kemudian ke setiap planet dan diakhiri dengan keberadaan obyek-obyek di tepi luar Tata Surya yang dikenal sebagai obyek Kuiper. Keindahan Tata Surya dipaparkan dengan bahasa yang sederhana untuk dipahami. Satu per satu planet dikupas sampai ke proses yang terjadi di dalamnya. Dan tak lupa definisi planet yang terbaru pun disertakan dengan mengacu pada peristiwa mengapa Pluto bukan planet lagi. Kehadiran klasifikasi baru planet katai juga dijelaskan dengan baik.Buku ini sangat baik untuk para pelajar yang ingin mengenal lebih dekat Tata Surya dan semua yang ada di dalamnya.

Namun bagaimanapun gamblangnya Tata Surya dijelaskan lewat penjelajahan ini, penjelajahan sesungguhnya dari para ilmuwa belumlah berakhir. Masih ada segudang misteri yang masih menanti untuk disingkapkan.

Sumber : langitselatan.com

Buku ini sangat disarankan bagi pecinta astronomi, khususnya para pemula. Saya pernah menggunakan buku ini (edisi lama) dan banyak sekali hal yang dapat dipelajari. Selamat belajar.

Binary Stars

2009-05-24T13:29:00.004+07:00

Looking through a telescope at the stars there is very little information we can gain from them. To be sure, we know what color they are and we can see that some are more luminous than others. If we use a spectrograph we can tell what elements they are made up from. From these facts alone, it is difficult to tell just how much mass they contain.

By looking at pairs of stars that orbit one another we can try to answer the question, how much mass do the stars have?

Binary stars can be of two fundamental types:

Visual Binaries
Optical Doubles

Alberio (Visual Binary)
Visual Binaries are stars that are clearly gravitational associated with one another. They orbit each other around a common center called the barycenter. Visual binaries can be seen optically through a telescope. Only a small portion of binary stars are visual binaries. In order to see a visual binary, the stars must be separated by fairly wide distances, and the orbital periods are usually very long.

Optical Doubles are stars that appear to lie close together, but in fact do not, they only appear to us from our earthly observation to be close together. One of the stars in the pair is actually behind the first star and very far away. The stars of an optical double are not gravitationally bound.

William Herschel began looking for optical doubles in 1782 with the hope that he would find a measurable parallax, by comparing a close star to the more distant star in an optical double.
Herschel did not find any optical binaries, but he did catalog hundreds of visual binaries. In 1804 Herschel had so many measurements of visual binaries that he concluded that a pair of stars known as Castor were orbiting one another. This was an important discovery, because it was the first time observational evidence clearly showed two objects in orbit around each other outside of the influence of our own Sun and Solar System.

Spectroscopic Binary
It is also possible to detect binary stars using a spectroscope. If two stars are orbiting each other they will both produce a spectrum. If the stars are close to being the same brightness it is possible to see different spectral lines from both stars. These stars are of particular interest because it can be used to determine the radial velocity of the orbit of the two stars. Stars appear red shifted when receding away from the earth and blue shifted as they approach. This effect is caused by the Doppler effect which distorts arriving light waves from the stars depending on the direction if their motion. A Spectroscopic binary will alternate between blue and red shifted spectral lines.

Spectroscopic binaries are not detectable if we are seeing the star head on because no Doppler shifts would be present in the spectrum. If the Doppler shifts are present in a single line of the spectrum, we are seeing the light from only one star and we call this a single-line spectroscopic binary. If we can see the light from both stars the Doppler shifts will alternate, split and merge depending on the positions of the two stars in their orbits. This is called a double-line spectroscopic binary.

One very important detail, we do not know how the orbits of the two stars are inclined to earth. This inclination could be any angle, for that bit of information we have to go back to visual methods in order to see the individual stars to determine the inclination of their orbits relative to earth. Even so we can not for certain determine the true inclination of the orbit so our mass calculation is only a lower limit to the masses of the two stars.

Radial velocities permit astronomers to compute the total mass for the two stars, they do not provide the masses for the individual stars and other methods must be used to make that determination

Eclipsing Binary
Another type of binary called the Eclipsing binary can be studied. The information gathered can be used to calculate the individual stellar masses and the diameters of the individual stars. It is rare to find two stars in orbit around one another to have orbital inclination where the stars pass in front of one another to form one point of light as seen from earth.
When the orbital inclination if the eclipsing binary is edge on to earth, the stars will seem to pass in front of one another as they orbit, when the light from the brighter star is eclipsed we will see a deep decline in the amount of light received from the star (6/25/95 in Figure 1) we call this primary minimum, also when the light from the dimmer star is blocked by the brighter the light received declines again, but not so deep and we call this secondary minimum (see 6/9/95 in Figure 1) , otherwise we are able to collect some or all of the light from both stars.

The pattern of these light changes is called a light curve and the data for it gathered by the use of a photometer, making periodic measurements until the eclipsing binaries produce a complete orbital cycle.

We use the mass vs. luminosity relationship to determine what the difference is between the individual masses, then using the mass of the entire system calculated from the radial velocity information, we can determine what the individual masses of the two stars should be. The photometeric data removes some of the uncertainty in regard to the inclination because the shapes of the light curves will be different for a partial eclipse than for a total eclipse.
ALGOL is one of the best known and most studied eclipsing binary stars. ALGOL is normally about 2.3 magnitude, but every 10 hours or so it will dim to about 3.4 magnitude, in other words ALGOL becomes 68% dimmer. I suspect that humanity has known about ALGOL's behavior for quite some time, since the Arabic name of ALGOL means "Demons Head", and ALGOL is associated with the severed head of Medusa. ALGOL is often referred to as the winking eye of the demon.

An eclipsing binary occurs when the orbital plane of the binary system is exactly When one star passes directly in front of the other, as viewed from Earth, we seen an eclipsing binary perpendicular to the plane of the sky.

Dwarf Nova or Recurrent Nova

When an otherwise normal star is associated with a white dwarf companion, a type of binary called a recurrent nova, or dwarf nova may occur. The normal star transfers mass onto an accretion disk which forms around the white dwarf. As material falls onto the accretion disk some of the material may be transferred to the white dwarf by turbulence in the accretion disk, this causes a sudden brightening of the white dwarf as the hydrogen is converted into helium.
If enough material from the accretion disk falls onto the white dwarf the hydrogen gas will become compressed and will not immediately fuse until a substantial increase in temperature occurs; the material will suddenly and violently erupt fusing into a runaway fusion reaction and a violent eruption called a dwarf nova occurs which will blow the accretion disk away, but it will not disturb the normal star.

Mass transfer will quickly resume and a new accretion disk will form. The cycle will continue until enough mass is drawn off the normal star to halt the reaction.

Mass transfer in any type of binary system will affect the evolutionary cycle of the two stars. The normal star will burn its fuel more slowly as mass is removed and the star cools down due to less internal heating from gravitational forces. It will also accelerate the evolution of the star receiving the mass, for the same reasons, more mass, more internal heating and the hastening of the fusion process.

If the material transfers very quickly, the gravitational forces will prevent the hydrogen from fusing by compressing it even further until the hydrogen gas becomes degenerate matter. Degenerate matter does not expand due to the increases in temperature so the mass of the white dwarf increases until it exceeds the Chandrasekhar Limit. When this happens the white dwarf will collapse and a type I supernova will occur which may destroy the companion star and the white dwarf changes into a neutron star or a black hole.

Burster
A similar event can occur when a normal star is associated with a pulsar, the energy given off will be mostly X-rays however, and instead of being called a dwarf nova or recurrent nova, it is called an X-ray burster or more simply a burster. We think that as normal hydrogen falls onto the accretion disk it is quickly converted into helium, when the helium reaches a depth of 1 meter, it will explosively convert helium into carbon producing X-rays. The longer the delay in fusing carbon, the larger and more violent the burst will be. The main difference between the recurrent nova and the burster is that the accretion disk will be hotter in the burster because it is already fusing hydrogen into helium, also the burst will produce mostly X-rays instead of visible light.

When a black hole is associated with a normal star, it will produce the same events as an X-ray burster and the only way to be sure that the companion is a blackhole, is when the mass of the compact object is greater than 3 solar masses. This is far too much mass for the companion to be a neutron star. The gravitational forces would cause the collapse of the star beyond the point of the neutrons to support themselves against the force of gravity and the star would collapse to a zero radius creating a black hole.

Calculation of star's properties with binary stars
Types of Binaries

Visual Binary: Can see both stars and follow their orbits over time.
Spectroscopic Binary: Cannot separate the two stars, but see their orbit motions as Doppler shifts in their spectral lines.
Eclipsing Binary: Can separate the stars, but see the total brightness drop when they periodically eclipse each other.

Visual Binaries --> Two stars orbiting about their center-of-mass.

Center of Mass
Two stars orbit about their center of mass.

Measure semi-major axis, a, from projected orbit & the distance.
Relative positions about the center give: M1/M2 = a2/a1

Measuring Masses
Newton's Form of Kepler's Third Law:
Procedure:
1. Measure the period, P, by following the orbit.
2. Measure semi-major axis, a, and the Mass Ratio, M1/M2, from the projected orbit on the sky.
3. Solve the equation above and separate Masses.

Problems
We need to follow an orbit long enough to trace it out in detail:

This can take decades
Need to work out the projection on the sky

Measurements depend on knowing the distance:

semi-major axis depends on d
derived mass depends on d^3

Small errors add up quickly (10% error in distance translates into a 30% error in the mass!).

Spectroscopic Binaries
Most binaries are too far away to be able to see both stars separately.
But, you can detect their orbital motions by the periodic Doppler shifts of the spectral lines:

• Determine the orbit period & size from the pattern of orbital velocities

Problems:
Cannot see the two stars separately:

Semi-major axis must be guessed from the orbit motions.
Can't tell how the orbit is tilted on the sky

Everything depends critically on knowing the distance.
Again...

Eclipsing Binaries
Two stars orbiting nearly edge-on to our line-of-sight.

See a periodic drop in brightness as one star eclipses the other.
Combine with spectra which measure orbital speeds

With the best data, one can find the masses of the stars without having to know the distance!!!

Problems
Eclipsing Binary stars are very rare.
Measurement of the light curves is complicated by details:

Partial eclipses yield less accurate numbers.
The atmospheres of the stars soften the edges.
Close binaries can be tidally distorted.

However, the best masses are from eclipsing binaries.

Source : many different sites

Soal Latihan : Mengenal Rasi Bintang

2009-05-10T11:58:00.004+07:00

Coba kenalilah beberapa rasi bintang yang ada di gambar berikut.

Tips :

Klik gambar tersebut untuk melihat ukuran penuhnya.
Beberapa rasi tersebut membentuk suatu pola tertentu yang digunakan sebagai penanda musim

Selamat mencoba

Soal Latihan Astronomi Dasar

2009-05-09T08:17:00.009+07:00

Silakan melatih pemahaman Anda tentang Astronomi dari beberapa soal yang saya post-kan.

Selamat belajar.

Soal Latihan Astronomi - 9 Mei 2009

Trivia Quiz:
Coba Anda sebutkan nama objek yang ada di foto berikut!

Why Are Galaxies Smooth?

2009-05-04T19:30:00.002+07:00

NGC 2841, a smooth galaxy. Credit: NASA

Look at the disk of any large spiral galaxy, and outwardly it appears smooth, with stars evenly distributed throughout. But when young stars are forming, they are clustered together in dense clouds of dust and gas. So what happens as the galaxy matures to allow for the smooth distribution seen in galaxies like the Milky Way? Using NASA’s Spitzer Space Telescope, an international team of astronomers has discovered streams of young stars flowing from their natal cocoons in distant galaxies. These distant rivers of stars provide an answer to one of astronomy’s most fundamental puzzles.

Astronomers know that the clusters where stars form begin to disappear when their ages reach several hundred million years. A few mechanisms are thought to explain this: some clusters evaporate when random internal motions kick out stars one by one, and other clusters disperse as a result of collisions among the clouds where they were born. Zooming out to mechanisms operating on larger scales still, shearing motions caused by the galaxy’s rotation around its center disperses the clusters of clusters of young stars.

“Our analysis now answers the grand puzzle. By finding a myriad of streams of young stars all over the disks of galaxies we studied, we see that the mechanism for pulling the clusters of young stars apart is shearing motions of the parent galaxy. These streams are the ‘missing link’ we needed to understand how the disks of galaxies evolve to look the way they do,” said team leader David Block of the University of the Witwatersrand in South Africa.

Crucial to this discovery was finding a way to image previously hidden young stellar streams in galaxies millions of light-years away. To do this the team used high-resolution infrared observations from the Spitzer.
Using infrared rather than visible light to look at the galaxies allowed the group to pick out stars at just the right age when the stars are just starting to spread out from their clusters.

Credit: NASA/ Spitzer team

“Spitzer observes in the infrared where 100-million-year-old populations of stars dominate the light,” noted co-author Bruce Elmegreen, from IBM’s Research Division in New York. “Younger regions shine more in the visible and ultraviolet parts of the spectrum, and older regions get too faint to see. So we can filter out all the stars we don’t want by taking pictures with an infrared camera.”

Infrared is also important because light in this part of the spectrum can penetrate the dense dust clouds surrounding the clusters where stars form.

“Dust blocks optical starlight very effectively,” said Robert Gehrz of the University of Minnesota, “but infrared light with its longer wavelength goes right around the dust particles blocking our view. This allows the infrared light from young stars to be seen more clearly.”

But even when the images are taken in the infrared, they are still dominated by the light from the smooth older disks of galaxies, not the faint tracks of young dispersing clusters. Special mathematical manipulations were needed to pick out the clusters, whose faint tracks can still be seen precisely because they are not smooth.

Team member Ivanio Puerari of the Instituto Nacional de Astrofisica, Optica y Electronica in Puebla, Mexico used a technique invented by mathematician Jean Baptiste Fourier in the early 1800’s. The technique is effectively a spatial filter that picks out structure on the physical scale where star formation occurs. “The structures cannot be seen on the original Spitzer images with the human eye,” noted Puerari.

“The combination of the Fourier filtering and infrared images highlighted regions of just the right size and the right age. To then unveil so many star streams in the disks of galaxies was unimaginable a year ago. This discovery continues to highlight the enormous potential of the Spitzer Space Telescope to make contributions none of us could have dreamed possible,” commented Giovanni Fazio from the Harvard-Smithsonian Center for Astrophysics, project leader for the Spitzer Infrared Array Camera team used to take the pictures, and co-author of the discovery.

“Galileo, as both astronomer and mathematician, would have been proud. It is a wonderful interplay between the use of astronomical observations and mathematics and computers, exactly 400 years since Galileo used his telescope to examine our Milky Way galaxy in 1609,” Fazio said

Source: Spitzer
Cited from : Universe Today

Soal Latihan Astrofisika

2009-04-24T15:15:00.001+07:00

Bagi yang berminat, silakan mencoba beberapa soal latihan yang akan melatih pemahaman Anda dalam hal Astrofisika.
Selamat belajar.

Soal Latihan Astrofisika 1 _ 2009

Brown Dwarfs Could Be More Common Than We Thought

2009-04-24T01:04:00.003+07:00

In 2007, something strange happened to a distant star near the centre of our galaxy; it underwent what is known as a ‘microlensing’ event. This transient brightening didn’t have anything to do with the star itself, it had something to do with what passed in front of it. 1,700 light years away between us and the distant star, a brown dwarf crossed our line of sight with the starlight. Although one would think that the star would have been blocked by the brown dwarf, its light was actually amplified, generating a flash. This flash was created via a space-time phenomenon known as gravitational lensing.

Although lensing isn’t rare in itself (although this particular event is considered the “most extreme” ever observed), the fact that astronomers had the opportunity to witness a brown dwarf causing it means that either they were very lucky, or we have to think about re-writing the stellar physics textbooks.

“By several measures OGLE-2007-BLG-224 was the most extreme microlensing event (EME) ever observed,” says Andrew Gould of Ohio State University in Columbus in a publication released earlier this month, “having a substantially higher magnification, shorter-duration peak, and faster angular speed across the sky than any previous well-observed event.”

OGLE-2007-BLG-224 revealed the passage of a brown dwarf passing in front of a distant star. The gravity of this small “failed star” deflected the starlight path slightly, creating a gravitational lens very briefly. Fortunately there were a number of astronomers prepared for the event and captured the transient flash of starlight as the brown dwarf focused the light for observers here on Earth.

From these observations, Gould and his team of 65 international collaborators managed to calculate some characteristics of the brown dwarf “lens” itself. The brown dwarf has a mass of 0.056 (+/- 0.004) solar masses, with a distance of 525 (+/- 40) parsecs (~1,700 light years) and a transverse velocity of 113 (+/- 21) km/s.

Although getting the chance to see this happen is a noteworthy in itself, the fact that it was a brown dwarf that acted as the lens is extremely rare; so rare in fact, that Gould believes something is awry.

“In this light, we note that two other sets of investigators have concluded that they must have been ‘lucky’ unless old-population brown-dwarfs are more common than generally assumed,” Gould said.

Either serendipity had a huge role to play, or there are far more brown dwarfs out there than we thought. If there are more brown dwarfs, something isn’t right with our understanding of stellar evolution. Brown dwarfs may be a more common feature in our galaxy than we previously calculate.

Sources: “The Extreme Microlensing Event OGLE-2007-BLG-224: Terrestrial Parallax Observation of a Thick-Disk Brown Dwarf,” Gould et al., 2009.
arXiv:0904.0249v1 [astro-ph.GA], New Scientist, Astroengine.com

Cited from : Universe Today

The Anatomy of a Solar Explosion

2009-04-16T06:17:00.003+07:00

Wouldn’t it be great if solar physicists could predict sun storms just like meteorologist predict hurricanes? Well, now perhaps they can. NASA’s twin STEREO observatories have made the first 3-D measurements of solar explosions, known as coronal mass ejections (CMEs), allowing scientists to see their size and shape, and image them as they travel approximately 93 million miles from the sun to Earth. With STEREO, scientists can now capture images of solar storms and make real-time measurements of their magnetic fields, much the same way that satellites allow forecasters to see the development of a hurricane. Eruptions from the sun’s outer atmosphere, or corona, can wreak havoc on satellites (and astronauts) in orbit or induce large currents in power grids on Earth, which can cause power disruptions or black outs.

“We can now see a CME from the time it leaves the solar surface until it reaches Earth, and we can reconstruct the event in 3D directly from the images,” said Angelos Vourlidas, a solar physicist at the Naval Research Laboratory, Washington, and project scientist for the Sun Earth Connection Coronal and Heliospheric Investigation aboard STEREO. In the video above, see some of the 3-D imagery, and hear Vourlidas talk about about the new findings.

CMEs spew billions of tons of plasma into space at thousands of miles per hour and carry some of the sun’s magnetic field with it. These solar storm clouds create a shock wave and a large, moving disturbance in the solar system. The shock can accelerate some of the particles in space to high energies, a form of “solar cosmic rays” that can be hazardous to spacecraft and astronauts. The CME material, which arrives days later, can disrupt Earth’s magnetic field, or magnetosphere, and upper atmosphere.

STEREO consists of two nearly identical observatories that make simultaneous observations of CMEs from two different vantage points. One observatory ‘leads’ Earth in its orbit around the sun, while the other observatory ‘trails’ the planet. STEREO’s two vantage points provide a unique view of the anatomy of a solar storm as it evolves and travels toward Earth. Once the CME arrives at the orbit of Earth, sensors on the satellites take in situ measurements of the solar storm cloud, providing a “ground truth” between what was seen at a distance and what is real inside the CME.

The combination is providing solar physicists with the most complete understanding to date of the inner workings of these storms. It also represents a big step toward predicting when and how the impact will be felt at Earth. The separation angle between the satellites affords researchers to track a CME in three dimensions, something they have done several times in the past few years as they have learned to use this new space weather tool.

“The in situ measurements from STEREO and other near-Earth spacecraft link the physical properties of the escaping CME to the remote images,” said Antoinette “Toni” Galvin, a solar physicist at the University of New Hampshire, and the principal investigator on STEREO’s Plasma and Suprathermal Ion Composition (PLASTIC) instrument. “This helps us to understand how the internal structure of the CME was formed and to better predict its impact on Earth.”

Until now, CMEs could be imaged near the sun but the next measurements had to wait until the CME cloud arrived at Earth three to seven days later. STEREO’s real-time images and measurements give scientists a slew of information—speed, direction, and velocity—of a CME days sooner than with previous methods. As a result, more time is available for power companies and satellite operators to prepare for potentially damaging solar storms.

Much like a hurricane’s destructive force depends on its direction, size, and speed, the seriousness of a CME’s effects depends on its size and speed, as well as whether it makes a direct or oblique hit across Earth’s orbit.

CMEs disturb the space dominated by Earth’s magnetic field. Disruptions to the magnetosphere can trigger the brightly colored, dancing lights known as auroras, or Northern and Southern Lights. While these displays are harmless, they indicate that Earth’s upper atmosphere and ionosphere are in turmoil.

Sun storms can interfere with communications between ground stations and satellites, airplane pilots, and astronauts. Radio noise from a storm can also disrupt cell phone service. Disturbances in the ionosphere caused by CMEs can distort the accuracy of Global Positioning System (GPS) navigation and, in extreme cases, induce stray electrical currents in long cables and power transformers on the ground.

The twin STEREO spacecraft were launched October 25, 2006, into Earth’s orbit around the sun.

Sources: NASA, APL

Cited from : Universe Today

Jawaban Soal Latihan Fotometri

2009-04-12T08:09:00.000+07:00

Beberapa hari yang lalu, saya pernah menge-post-kan beberapa soal latihan fotometri. Jika Anda sudah mencobanya, coba bandingkan dengan jawaban yang bisa di download dari link di bawah ini.

Selamat belajar.
Jawaban Soal Latihan Soal Fotometri

Soal Latihan 2 : Spektroskopi

2009-04-09T08:19:00.002+07:00

Karena tahap seleksi peserta olimpiade sains nasional Astronomi 2009 semakin dekat, saya mencoba membantu dengan memberikan beberapa soal latihan lagi. Kali ini, soal-soal ini bertema spektroskopi. Silakan dicoba dan didiskusikan dengan guru/tutor/teman.

Selamat belajar.
Soal Latihan Spektroskopi_2009

Refraksi Atmosfer

2009-04-08T13:19:00.007+07:00

Posisi benda langit yang tampak di langit sebenarnya berbeda dengan posisi fisiknya, salah satu sebab adalah karena efek refraksi.

Efek refraksi pada saat Matahari atau Bulan terbenam
Saat Matahari atau Bulan terbit/terbenam, jarak zenit dari pusat kedua benda tersebut adalah 90^o. Refraksi yang terjadi saat itu disebut sebagai refraksi horisontal.

Refraksi horisontal saat benda langit terbit/terbenam adalah 35‟. Jika jarak zenit = 90^o, maka jarak zenit benar adalah 90^o35‟.

Efek refraksi pada asensiorekta dan deklinasi
- α’ – α = R sec δ’ sin η
- δ’ – δ = R cos η
dengan η adalah sudut paralaktik

Koreksi semi diameter
Pada saat Matahari terbenam, z = 90^o, h’ = 0^o, maka :
- jarak zenit piringan Matahari adalah : z = 90^o + R_{z = 90 deg}
- tinggi pusat Matahari adalah : h = 0^o - R_{z = 90 deg}

Matahari dikatakan terbit jika batas atas piringan mulai muncul di horison, dan terbenam jika batas piringan sudah terbenam di horison, maka z dan h harus dikoreksi oleh semidiameter piringan Matahari, S, sehingga :
z = 90^o + R_{z = 90 deg} + S
h = 0^o - R_{z = 90 deg} - S

Jadi, saat Matahari atau Bulan terbit atau terbenam :
h_{sun = - 0^o50’
h_moon = + 0^o08

Koreksi ketinggian di atas muka laut
Bidang horison pengamat di Bumi bergantung kepada ketinggian pengamat. Jika pengamat berada pada ketinggian l (meter) dari muka laut, maka sudut kedalaman (angle of dip), θ, adalah:
θ = 1’.93√l (dalam satuan menit busur).

Jika efek refraksi diperhitungkan, maka :
θ = 1’.78√l (dalam satuan menit busur)

Jarak ke horison-laut, dituliskan dengan :
d = 3.57√l (dalam km)

Jika efek refraksi diperhitungkan, maka :
d = 3.87√l (dalam km)

Soal Latihan
The White Bear from the previous International Astronomy Olympiad is still sitting at the North Pole. But this year a follower is appeared – a Penguin is sitting at the South Pole. Recently, after the ending of polar night, the Penguin observed the sunrise. What did the Bear observe this time? Draw what the White Bear saw at the moment when the Penguin observed exactly half of the solar disk on the horizon. Assume that the Earth is spherical. The answer should be explained by drawing a figure with an image of the Bear on North Pole; necessary sizes or angular sizes should be in the picture. Recollect for yourself the necessary information about the animals. (taken from IAO)}

Soal Latihan Fotometri

2009-04-05T10:50:00.002+07:00

Karena sudah semakin dekat dengan seleksi peserta olimpiade astronomi 2009, saya berikan beberapa soal sebagai latihan tentang fotometri.
Selamat belajar

Soal Latihan 2009 - Fotometri

Waktu Sideris dan Waktu Sinodis

2009-03-26T07:22:00.004+07:00

Sidereal time is a measure of the position of the Earth in its rotation around its axis, or time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical to, the motion of stars. They differ by the precession of the vernal equinox in right ascension relative to the stars.

Earth's sidereal day also differs from its rotation period relative to the background stars by the amount of precession in right ascension during one day (8.4 ms). Its J2000 mean value is 23h56m4.090530833s. Etymology of sidereal is from Latin "sidereus" from sidus, sider- = star. Therefore, its meaning relates to a measurement of time relative to the position of the stars.

Definition

Local Sidereal Time (LST) = RA + HA
Greenwich Sidereal Time (GST) is the LST at the Greenwich Meridian

Sidereal time is defined as the hour angle of the vernal equinox. When the meridian of the vernal equinox is directly overhead, local sidereal time is 00:00. Greenwich Sidereal Time is the hour angle of the vernal equinox at the prime meridian at Greenwich, England; local values differ according to longitude. When one moves eastward 15° in longitude, sidereal time is larger by one hour (note that it wraps around at 24 hours). Unlike computing local solar time, differences are counted to the accuracy of measurement, not just in whole hours. Greenwich Sidereal Time and UT1 differ from each other by a constant rate (GST = 1.00273790935 × UT1). Sidereal time is used at astronomical observatories because sidereal time makes it very easy to work out which astronomical objects will be observable at a given time. Objects are located in the night sky using right ascension and declination relative to the celestial equator (analogous to longitude and latitude on Earth), and when sidereal time is equal to an object's right ascension, the object will be at its highest point in the sky, or culmination, at which time it is best placed for observation, as atmospheric extinction is minimized.

Sidereal time and solar time
Solar time is measured by the apparent diurnal motion of the sun, and local noon in solar time is defined as the moment when the sun is at its highest point in the sky (exactly due south or north depending on the observer's latitude and the season). The average time taken for the sun to return to its highest point is 24 hours.

During the time needed by the Earth to complete a rotation around its axis (a sidereal day), the Earth moves a short distance (approximately 1°) along its orbit around the sun. Therefore, after a sidereal day, the Earth still needs to rotate a small extra angular distance before the sun reaches its highest point. A solar day is, therefore, nearly 4 minutes longer than a sidereal day.

The stars, however, are so far away that the Earth's movement along its orbit makes a generally negligible difference to their apparent direction (see, however, parallax), and so they return to their highest point in a sidereal day. A sidereal day is almost 4 minutes shorter than a mean solar day.

Another way to see this difference is to notice that, relative to the stars, the Sun appears to move around the Earth once per year. Therefore, there is one less solar day per year than there are sidereal days. This makes a sidereal day approximately ^365.24⁄_366.24 times the length of the 24-hour solar day, giving approximately 23 hours, 56 minutes, 4.1 seconds (86,164.1 seconds).

Sidereal time vs solar time. Above left: a distant star (the small red circle) and the Sun are at culmination, on the local meridian. Centre: only the distant star is at culmination (a mean sidereal day). Right: few minutes later the Sun is on the local meridian again. A solar day is complete.

Precession effects
The Earth's rotation is not simply a simple rotation around an axis that would always remain parallel to itself. The Earth's rotational axis itself rotates about a second axis, orthogonal to the Earth's orbit, taking about 25,800 years to perform a complete rotation. This phenomenon is called the precession of the equinoxes. Because of this precession, the stars appear to move around the Earth in a manner more complicated than a simple constant rotation.

For this reason, to simplify the description of Earth's orientation in astronomy and geodesy, it is conventional to describe Earth's rotation relative to a frame which is itself precessing slowly. In this reference frame, Earth's rotation is close to constant, but the stars appear to rotate slowly with a period of about 25,800 years. It is also in this reference frame that the tropical year, the year related to the Earth's seasons, represents one orbit of the Earth around the sun. The precise definition of a sidereal day is the time taken for one rotation of the Earth in this precessing reference frame.

Exact duration and its variation

A mean sidereal day is about 23 h 56 m 4.1 s in length. However, due to variations in the rotation rate of the Earth the rate of an ideal sidereal clock deviates from any simple multiple of a civil clock. In practice, the difference is kept track of by the difference UTC–UT1, which is measured by radio telescopes and kept on file and available to the public at the IERS and at the United States Naval Observatory.

Given a tropical year of 365.242190402 days from Simon et al. this gives a sidereal day of 86,400 × ^{365.242190402}⁄_{366.242190402}, or 86,164.09053 seconds.

According to Aoki et al., an accurate value for the sidereal day at the beginning of 2000 is ¹⁄_{1.002737909350795} times a mean solar day of 86,400 seconds, which gives 86,164.090530833 seconds. For times within a century of 1984, the ratio only alters in its 11th decimal place. This web-based sidereal time calculator uses a truncated ratio of ¹⁄_{1.00273790935}.

Because this is the period of rotation in a precessing reference frame, it is not directly related to the mean rotation rate of the Earth in an inertial frame, which is given by ω=2π/T where T is the slightly longer stellar day given by Aoki et al. as 86,164.09890369732 seconds. This can be calculated by noting that ω is the magnitude of the vector sum of the rotations leading to the sidereal day and the precession of that rotation vector. In fact, the period of the Earth's rotation varies on hourly to interannual timescales by around a millisecond, together with a secular increase in length of day of about 2.3 milliseconds per century which mostly results from slowing of the Earth's rotation by tidal friction.

Source : wikipedia, Polaris Project,Positional Astronomy

Example:

Teleskop Hubble Menunjukkan Bukti Keberadaan Dark Matter di sekitar galaksi kecil

2009-03-21T04:39:00.007+07:00

Hubble Space Telescope (HST) milik NASA/ESA telah menemukan serangkaian bukti kuat tentang keberadaan dark matter di halo galaksi.

HST mengamati kluster galaksi Perseus dan menemukan banyak galaksi kecil yang tetap utuh sementara galaksi besar di sekitarnya "terkoyak" oleh gaya gravitasi satu sama lain.

Gambar yang diperoleh HST menunjukkan bukti lebih lanjut bahwa galaksi kecil tersebut dikelilingi oleh dark matter yang melindunginya dari gaya gravitasi galaksi tetangga yang bisa menghancurkannya.

Dark matter adalah sejenis materi yang tidak memancarkan radiasi (sehingga dianggap "dark" karena tidak teramati secara visual) tetapi dapat dideteksi dari efek gaya gravitasi yang ditimbulkan pada objek yang teramati, seperti bintang, gas dan debu, dll. Dark matter mendominasi materi yang ada di alam semesta ini.

Astronom Christopher Conselice dari Universitas Nottingham, UK mengatakan bahwa timnya (beliau memimpin tim pengamatan dengan HST) terkejut ketika menemukan begitu banyak galaksi kerdil (dwarf galaxy) di bagian inti kluster ini (Perseus, red) yang begitu mulus dengan bentuk bulat dan tidak ada tanda-tanda adanya gangguan gravitasi dari galaksi lain. Galaksi kerdil tersebut adalah galaksi yang sudah sangat tua sehingga jika ada sesuatu yang bisa menghancurkannya (gaya gravitasi galaksi lain, misalnya) pasti sudah akan terjadi saat ini. Galaksi - galaksi ini pastilah didominasi oleh dark matter.

Galaksi kerdil tersebut mungkin mengandung dark matter lebih banyak daripada galaksi spiral. Hal ini disimpulkan berdasarkan pengamatan bahwa galaksi spiral di kluster Perseus hancur (bentuknya terdistorsi) sedangkan galaksi kerdil tersebut tidak. Meskipun begitu, Concelice tidak dapat mengatakan bahwa kandungan dark matter di galaksi kerdil ini lebih tinggi dibandingkan galaksi kita, BimaSakti (Milky Way).

Diajukan pertama kali oleh astronom Swiss Fritz Zwicky, dark matter dianalogikan seperti lem yang mengikat galaksi - galaksi. Astronom percaya bahwa dark matter mempunyai perna penting dalam pembentukan galaksi lewat tarikan gravitasinya.

Observasi dengan Hubble's Advanced Camera for Surveys menemukan 29 galaksi kerdil elips di Kluster Perseus yang berjarak 250 juta tahun cahaya dan merupakan salah satu kluster galaksi terdekat.

Karena dark matter tidak dapat "dilihat", astronom mendeteksi keberadaannya dengan pengukuran tidak langsung. Metode yang umum adalah dengan mengukur kecepatan dari masing-masing bintang atau kelompok bintang seiring gerakan acaknya atau gerakannya mengitari galaksi.

Kluster Perseus terlalu jauh bagi teleskop untuk mengamati bintang tunggal dan mengukur kecepatan geraknya. Jadi, Conselice dan timnya menemukan teknik baru untuk menemukan dark matter di galaksi kerdil ini dengan menentukan kontribusi massa tambahan minimum dari dark matter yang harus dipunyai galaksi kerdil untuk melindunginya dari kehancuran akibat gaya tarik gravitasi dari galaksi lain yang lebih besar ukurannya.

Dengan mempelajari galaksi - galaksi kerdil ini secara detail hanya dimungkinkan oleh ketajaman resolusi Hubble's Advanced Camera for Surveys. Conselice dan timnya pertama kali mengamati kluster Perseus dengan teleskop WIYN di Kitt Peak National Observatory (dipunyai dan dioperasikan oleh konsorsium WIYN, yang terdiri dari University of Wisconsin, Indiana University, Yale University, dan National Optical Astronomy Observatory). Hasil pengamatan yang diperoleh dengan teleskop tersebut hanya mengindikasikan bahwa galaksi - galaksi yang diamati Concelice dan timnya sangat "smooth" dan didominasi oleh dark matter tetapi teleskop tersebut tidak cukup resolusinya untuk melakukan pengamatan secara detail. Oleh sebab itu, Concelice dan timnya menggunakan HST untuk melakukan pengamatan ini.

Sumber : ESA

Trivia : Two Objects

2009-03-12T10:24:00.002+07:00

Can you mention the name of these two objects (see the picture above)? Are they included in Messier Catalog's objects? If yes, mention its Messier number.

You can submit your answer and discuss with other reader in the comment section.

GLOBE at Night 2009 - Can You See the Stars?

2009-03-09T00:43:00.000+07:00

Turning out the lights for "Earth Hour" is going to be a great way to demonstrate caring about climate changes by turning off the lights - but what about the impact that light pollution has on our skies? 2008 marked a monumental shift in human history when the number of people living in cities exceeded half the people on Earth. Because of the ambient light of urban landscapes, many city dwellers have never seen a sky full of stars. Are you interested in helping science study the impact of lighting in your area? Then step inside and learn more about GLOBE…

GLOBE at Night is a wonderful way for everyone around the world to participate as a citizen-sciencist to raise public awareness of the impact of artificial lighting on local environments. This event encourages everyone - students, educators, dark sky advocates and the general public - to measure the darkness of their local skies and contribute their observations online to a world map. GLOBE at Night is a centerpiece of the Dark Skies Awareness Global Cornerstone Project for the International Year of Astronomy (IYA) in 2009, and we need people - just like you - to get involved! Data collection and online reporting is simple and user-friendly.

Led by the educational outreach staff at the National Optical Astronomy Observatory and the University Corporation for Atmospheric Research GLOBE Program, the GLOBE at Night campaign will take place for a 4th year from March 16-28, 2009. “The geographic reach of the GLOBE at Night program exceeded our wildest expectations,” said Connie Walker, an astronomer and science education specialist at the National Optical Astronomy Observatory (NOAO), one of the event’s major co-sponsors. “We fell a few hundred short of our target of 5,000 total observations, but the engagement and excitement of large family groups, and dozens of school children participating in the activity together, more than make up for a few less data points.”

Over the past 3 years, tens of thousands of citizen-scientists around the world have contributed measurements of their local sky brightness to a growing global database in two ways: simple unaided-eye observations toward the constellation Orion and quantative digital measurements through a handheld, well-calibrated sky-brightness meter. For the first method, citizen-scientists take data on light pollution levels by comparing what they see toward Orion, with star maps showing different stellar brightness limits. The basic idea is to look for the faintest stars and match them to one of seven star maps of progressively fainter limiting magnitudes. For the second method, digital sky-brightness meters are used for more precise measurements. The low-cost digital Sky Quality Meters (SQMs), manufactured by Unihedron, can make a highly repeatable, direct measurement of integrated sky brightness. The newly available second-generation of SQM-Ls being used this year by several GLOBE at Night sites has a cone-shaped “field of view” that is three times more narrow than the older model. This specifically aids its use in city environments, where surrounding lights or buildings may affect the readings.

To learn the five easy steps to participate in either type of GLOBE at Night program and to obtain important information on light pollution, stellar magnitudes, the mythology of Orion, how to find Orion, how to obtain your latitude and longitude, and how to use an SQM, see the GLOBE at Night website. No prior experience is necessary and all the information you need to participate is right there - along with downloads for activity kits for families, teachers and invididuals in six different languages. All observations will be available online via Google Earth and as downloadable datasets, too.

Thanks to an international network of partners, GLOBE reaches people around the world, and during their first two years managed 20,000 observations from a total of 100 countries. This year, they're hoping for an even greater success rate and within weeks of submitting your data, a world map showing the results of your studies will be made available. Using this information, you can then compare the data to previous studies, as well as satellite data and population density data. Collecting information from mulitple locations inside a single city or region is highly encourged, and would make a great class project or astronomy club activity!

By activity participating in projects like GLOBE, you can make difference. More measurements made each year and over the next few years will allow for in more depth analysis. More measurements within a city will provide maps of higher resolution and comparisons between years would allow people to monitor changes. Just like our other Earthly environments, monitoring our lighting environment will allow us as citizen-scientists to identify and preserve dark sky locations in cities or catch an area developing too quickly and influence people to make smart choices in lighting by providing them with informed neighbors. As just everyday, ordinary people, we can impact what happens by educating ourselves and others. If more and more people took a few minutes during the March 2009 campaign to measure sky brightness either toward Orion with the unaided-eye or toward zenith with a Sky Quality Meter (or both!), their measurements - and yours - will make a world of difference!

Cited from : Universe Today - Tammy Plotner

Article : Watching Venus Glow In The Dark

2009-03-08T13:11:00.003+07:00

Atmospheric investigations by Venus Express

ESA’s Venus Express spacecraft has observed an eerie glow in the night-time atmosphere of Venus. This infrared light comes from nitric oxide and is showing scientists that the atmosphere of Earth’s nearest neighbour is a temperamental place of high winds and turbulence.

Unfortunately, the glow on Venus cannot be seen with the naked eye because it occurs at the invisible wavelengths of infrared. ESA’s Venus Express, however, is equipped with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument, which can see these wavelengths.

VIRTIS has made two unambiguous detections of the so-called nightglow for nitric oxide at Venus. This is the first time such infrared detections have been made for any planet and provide a new insight into Venus’s atmosphere.

“The nightglow can give us a lot of information,” says Antonio García Muñoz, who was at the Australian National University when the research was carried out; he is now located at the Instituto de Astrofísica de Canarias, Tenerife, Spain. "It can provide details about the temperature, wind direction, composition and chemistry of an atmosphere."

The nightglow is ultimately caused by the Sun’s ultraviolet light, which streams into a planet’s atmosphere and breaks the molecules up into atoms and other simpler molecules. The free atoms may recombine again and, in specific cases, the resulting molecule is endowed with some extra energy that is subsequently lost in the form of light. On the day-side of the planet, any atoms that do find their way back together are outshone by the sunlight falling into the atmosphere.

But on the night-side, where atoms are transported by a vigorous diurnal circulation, the glow can be seen with appropriate instruments, such as VIRTIS.

A nitric oxide nightglow in the infrared has never been observed in the atmospheres of Mars or Earth, although we know that the necessary nitric oxide molecules are present because they have been observed in ultraviolet.

Nightglow in Venus’s atmosphere

The nightglow on Venus has been seen at infrared wavelengths before, betraying oxygen molecules and the hydroxyl radical, but this is the first detection of nitric oxide at those wavelengths. It offers data about the atmosphere of Venus that lies above the cloud tops at around 70 km. The oxygen and hydroxyl emissions come from 90-100 km, whereas the nitric oxide comes from 110-120 km altitude.

Yet, even VIRTIS cannot see the nitric oxide nightglow all the time because it is often just too faint. “Luckily for us, Venus has a temperamental atmosphere,” says García Muñoz, “Packets of oxygen and nitrogen atoms are blown around.” Sometimes these become dense enough to boost the brightness of the nightglow, making it visible to VIRTIS.

Venus Express can observe the three nightglow emissions simultaneously, and this gives rise to a mystery. The nightglows from the different molecules do not necessarily happen together. “Perhaps when we have more observations, we will understand the correlation between them,” says García Muñoz.

In order to do that, the VIRTIS team plans to continue monitoring the planet, building up a database of this fascinating phenomenon.

Cited from : ESA

Trivia Question : Guess The Name Of This Object

2009-03-01T11:33:00.006+07:00

It's been long time since the last time I posted a trivia question. This one is an easy one. Can you mention the name of the object?

Pulsar Purba Yang Masih Aktif

2009-02-28T23:58:00.000+07:00

Artist concept of ancient pulsar J0108. Image credit: X-ray: NASA/CXC/Penn State/G.Pavlov et al. Optical: ESO/VLT/UCL/R.Mignani et al. Illustration: CXC/M. Weiss

Pulsar ini mungkin sudah berumur tua tetapi belum mati. Chandra X-Ray Observatory telah menemukan pulsar terisolasi (bukan dalam sistem bintang ganda) yang paling tua. Meskipun pulsar ini termasuk pulsar tua tetapi objek eksotis ini masih sangat aktif. Berdasarkan pengamatan pada panjang gelombang radio, pulsar ini, PSR J0108-1431 (atau disebut J0108 saja) telah berusia 200 juta tahun. Di antara pulsar-pulsar sejenis (pulsar terisolasi) , pulsar ini 10 kali lebih tua daripada yang pernah ditemukan sebelumnya. Tim astronom yang dipimpin oleh George Pavlov dari Universitas Penn mengamati Jo1o8 dalam panjang gelombang sinar-X dengan Chandra dan menemukan pulsar ini nampak lebih terang (pada panjang gelombang sinar-X) dibandingkan yang diperkirakan untuk pulsar yang sudah berumur ratusan juta tahun.

Pulsar ini berjarak 770 tahun cahaya, merupakan salah satu pulsar terdekat yang kita ketahui.

Pulsar terbentuk ketika bintang yang lebih masif dibandingkan Matahari runtuh dalam peristiwa ledakan Supernova. Sisa dari ledakan tersebut adalah inti bintang, berukuran kecil (~10 km) dan berdensitas sangat besar. Benda inilah yang dikenal dengan istilah bintang neutron (karena sebagian besar komponennya adalah neutron). Di saat kelahirannya, bintang neutron (yang mengandung material paling padat di seluruh alam semesta) berotasi sangat cepat, hingga 100 kali putaran per detik. Pancaran radiasi yang berputar terlihat seperti sinyal mercusuar bagi pengamat yang jauh. Oleh sebab itu, bintang neutron disebut juga "pulsar" (pulsating star). Sebagai tambahan informasi, pada awalnya astronom menganggap pulsar dan binang neutron (yang masih berupa objek hipotetis) adalah 2 objek yang berbeda, namun akhirnya diketahui bahwa kedua objek tersebut adalah sama.

Astronom mengamati adanya perlambatan rotasi pulsar secara gradual seiring pulsar memancarkan radiasinya. Pengamatan radio terhadap Jo1o8 menunjukkannya sebagai salah satu pulsar tertua dan teredup yang diketahui dan berotasi dengan kecepatan sedikit diatas 1 putaran per detik.

J0108 in a combination of optical and X-ray. Image credit: X-ray: NASA/CXC/Penn State/G.Pavlov et al. Optical: ESO/VLT/UCL/R.Mignani et al.

Sebagian energi yang hilang dari J0108 seiring rotasinya yang semakin melambat dikonversi menjadi radiasi sinar-X. Efisiensi proses ini di J0108 ditemukan lebih tinggi dibandingkan pulsar - pulsar yang telah terdeteksi sebelumnya.

Nampaknya ada dua jenis emisi sinar X yang dihasilkan di J0108 :

Emisi dari partikel yang berputar dalam lintasan spiral mengitari medan magnet pulsar
Emisi dari area yang dipanaskan di sekeliling kutub magnetik bintang neutron

Mengukur temperatur dan ukuran dari area yang dipanaskan tersebut dapat memberikan pemahaman yang lebih mendalam terhadap properti permukaan bintang neutron yang luar biasa dan proses akselerasi partikel bermuatan oleh pulsar.

Pular yang lebih muda dan lebih terang yang umum dideteksi oleh teleskop radio dan teleskop sinar-X bukanlah representasi dari keseluruhan popluasi objek sejenisnya. Oleh sebab itu, mengamati objek seperti J0108 akan membantu astronom untuk mengamati sifat dari rentang yang lebih luas. Dengan umur mencapai ratusan juta tahun, J0108 hampir ada di kondisi yang disebut "pulsar death line", di saat radiasinya diperkirakan sudah hilang dan hampir tidak mungkin diamati.

Bagi astronom, untuk memahami sifat 'dying pulsar' perlu mempelajari radiasi sinar-X nya. Penemuan ini membuka kesempatan baru bagi astronom untuk menemukan pulsar sejenis lewat pancaran sinar-X nya.

Pulsar ini bergerak dengan kecepatan 440.000 mil per jam dan saat ini sedang bergerak ke arah selatan dari bidang galaksi Bima Sakti (Milky Way) tetapi karena kecepatannya kurang dari kecepatan lepas galaksi, pulsar ini akan bergerak memutar kembali menuju bidang galaksi pada arah yang berlawanan.

Sumber : NASA dan Universe Today

Penemuan Baru tentang Proses Pembentukan Galaksi Kerdil (Dwarf Galaxy)

2009-02-19T21:56:00.009+07:00

NASA's Galaxy Evolution Explorer reveals, for the first time, dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe. Credit: NASA/JPL-Caltech/DSS

Astronom, dengan menggunakan Galaxy Evolution Explorer (GALEX) milik NASA, telah menemukan galaksi baru di rasi Leo yang kelihatannya terbentuk dari gas yang hanya sedikit mengandung materi gelap (dark matter) dan unsur logam. Gas ini mungkin merupakan gas sisa awal pembentukan alam semesta. Sebelumnya, diperkirakan bahwa materi gelap dan unsur logam merupakan unsur pembangun (building block) untuk pembentukan galaksi.

Galaksi kerdil adalah kumpulan bintang-bintang berskala relatif kecil yang seringkali mengorbit galaksi lain yang lebih besar (misalkan : LMC dan SMC yang mengorbit galaksi kita, Milky Way). Meskipun belum pernah teramati sebelumnya, para peneliti mengatakan bahwa galaksi kerdil tipe baru ini mungkin umum ada di epoch alam semesta yang lebih jauh dan lebih awal (karena semakin jauh jaraknya, semakin jauh kita melihat ke masa lampau). Hal ini disebabkan pada masa (epoch) ini, gas yang mengandung sedikit materi gelap dan unsur logam masih banyak.

Galaksi kerdil yang baru ini ada di konstelasi (rasi) Leo, berupa sebuah kumpulan gas raksasa yang terdiri dari hidrogen dan helium. Awan gas ini diperkirakan adalah objek primordial, yang merupakan sisa material dari masa lalu yang tidak berubah sejak awal alam semesta.

Objek ini telah diamati selama beberapa dekade menggunakan teleskop bertaraf dunia, yang beroperasi pada daerah gelombang radio dan optik. Sebelumnya, tidak pernah teramati adanya bintang di daerah tersebut tetapi ketika diamati dengan Galaxy Evolution Explorer yang sangat peka terhadap panjang gelombang ultraviolet, teramati bukti adanya proses pembentukan bintang raksasa (massive star). Hal ini tidak pernah diduga sebelumnya, ada peristiwa pembentukan galaksi dari sebuah awan gas primordial.

Alam semesta lokal kita mengandung dua galaksi besar, Milky Way (Bimasakti) dan galaksi Andromeda. Masing-masing galaksi mengandung ratusan milyar bintang. Selain itu, ada juga galaksi Triangulum yang mengandung puluhan milyar bintang. Alam semesta lokal kita juga mengandung lebih dari 40 galaksi kerdil, yang hanya memiliki beberapa milyar bintang. Materi gelap yang tak terlihat, terdeteksi dari pengaruh gravitasi-nya, adalah komponen yang utama dari kedua tipe galaksi tersebut, galaksi besar dan kerdil, dengan perkecualian jenis tidal dwarf galaxy.

Tidal dwarf galaxy terkondensasi dari gas yang didaur ulang dari galaksi lain dan telah dipisahkan dari materi gelap, yang semula terkait dengan gas tersebut. Jenis galaksi ini terbentuk ketika terjadinya tabrakan antar galaksi dan interaksi gravitasi antara kedua galaksi yang bertabrakan tersebut. Material galaksi ditarik menjauh dari galaksi induknya dan bagian halo galaksi yang mengandung materi gelap.

Bagian-bagian sebuah galaksi spiral

Dua galaksi yang sedang bertabrakan

Karena kekurangan unsur materi gelap, galaksi baru yang diamati di rasi Leo tersebut menyerupai tidal dwarf galaxy (galaksi yang terbentuk akibat gaya pasang surut (tidal force) ketika terjadi tabrakan antar galaksi) tetapi memiliki perbedaan yang mendasar (fundamental). Material gas yang membentuk tidal dwarf galaxy merupakan sisa material dari sebuah galaksi, yang telah diperkaya dengan unsur logam (unsur yang lebih berat daripada helium) yang diproduksi seiring proses evolusi bintang (bintang raksasa di akhir hidupnya akan melepaskan unsur logam saat meledak menjadi supernova). Galaksi yang ditemukan di rasi Leo tersebut terbentuk dari material gas yang tidak memiliki kandungan unsur logam. Penemuan ini akan memberikan tantangan baru untuk bagi astronom untuk mempelajari proses pembentukan bintang dari gas yang belum diperkaya dengan unsur logam.

Material gas yang masih murni (seperti yang ditemukan di Leo Ring) mungkin merupakan hal yang umum di masa alam semesta yang lebih awal dan hal ini akan berakibat pada lebih besarnya kemungkinan pembentukan galaksi kerdil yang kekurangan materi gelap dan unsur logam.

The forming dwarf galaxies shine in the far ultraviolet spectrum, rendered as blue in the call-out on the right hand side of this image. Near ultraviolet light, also obtained by the Galaxy Evolution Explorer, is displayed in green, and visible light from the blue part of the spectrum here is represented by red. The clumps (in circles) are distinctively blue, indicating they are primarily detected in far ultraviolet light. The faint blue overlay traces the outline of the Leo Ring, a huge cloud of hydrogen and helium that orbits around two massive galaxies in the constellation Leo (left panel). Credit: NASA/JPL-Caltech/DSS

Sumber : Universe Today

Hilangnya Air di Venus

2009-02-08T20:45:00.018+07:00

Misi luar angkasa, Venus Express, menemukan untuk pertama kalinya proses hilangnya atmosfer di belahan Venus yang mengalami siang (day-side). Tahun 2007, misi tersebut menemukan bahwa sebagian besar atmosfer yang hilang tersebut lepas dari belahan malam Venus (night-side). Dari dua penemuan ini, ilmuwan planet dapat lebih memahami apa yang terjadi dengan air yang ada di Venus, yang diduga pada masa lampau memiliki air sebanyak di Bumi.

Instrumen magnetometer di wahana ruang angkasa tersebut mendeteksi tanda-tanda lepasnya gas hidrogen di belahan siang Venus. Proses ini sudah diduga sebelumnya oleh ilmuwan tetapi baru pertama kali diukur.

Wahana Venus Express dapat mengivestigasi proses ini karena orbitnya yang strategis. Wahana ini menempuh orbit yang sangat eliptikal dan melewati bagian kutub planet Venus.

Air merupakan molekul kunci di Bumi karena keberadaan air memungkinkan keberlangsungan kehidupan yang ada. Astronom percaya bahwa planet Venus memiliki air sebanyak di Bumi karena Venus dan Bumi berukuran hampir sama besar dan terbentuk pada saat yang hampir bersamaan. Namun, pada saat ini proporsi air di kedua planet tersebut berbeda sangat ekstrim. Atmosfer dan lautan di Bumi mengandung 100 000 kali air dibandingkan total air di Venus. Meskipun jumlah air di Venus sangat sedikit, ditemukan bahwa setiap detiknya terjadi pelepasan 2 x 10²⁴ atom hidrogen dari belahan siang Venus. Atom hidrogen merupakan salah satu komponen dalam molekul air (H₂O).

Tahun 2007, Analyser of Space Plasma and Energetic Atoms (ASPERA) yang terpasang pada wahana Venus Express menunjukkan ada sejumlah besar hidrogen dan oksigen lepas dari Venus pada belahan malam Venus. Secara kasar diperoleh perbandingan atom hidrogen yang hilang sekitar 2 kali jumlah atom oksigen yang lepas. Hal ini mengindikasikan molekul air dipecah menjadi atom-atom penyusunnya di atmosfer Venus (H₂O --> 2H + O).

Matahari tidak hanya memancarkan cahaya dan panas ke ruang angkasa, tetapi juga menghasilkan angin Matahari (solar wind) secara terus menerus. Angin Matahari adalah aliran partikel bermuatan dari Matahari. Angin Matahari membawa medan listrik dan medan magnet ke seluruh penjuru tata surya dan mungkin "menabrak" planet-planet.

Tidak seperti Bumi, Venus tidak memiliki medan magnet. Keberadaan medan magnet di Bumi sangat penting karena berfungsi melindungi atmosfer Bumi (dan isinya tentunya) dari keganasan angin Matahari. Sedangkan Venus, saat angin Matahari menabrak bagian atas atmosfer planet tersebut, angin Matahari akan ikut membawa pergi partikel-partikel. Ilmuwan planet memperkirakan mekanisme inilah yang menyebabkan air di Venus hilang. Proses ini diperkirakan telah terjadi sejak Venus terbentuk, sekitar 4,5 milyar tahun yang lalu.

Meskipun ilmuwan telah menemukan peristiwa lepasnya molekul air (dalam wujud atom - atom pembentuknya, hidrogen dan oksigen) tetapi ilmuwan masih belum mengetahui berapa banyak air yang telah hilang dengan mekanisme ini.

Penemuan ini telah membawa ilmuwan ke tingkat pemahaman yang lebih detail tetapi hal ini tidak berarti ilmuwan telah memahami hal ini secara lengkap. Untuk menyakinkan bahwa atom hidrogen yang lepas dari belahan siang Venus, ilmuwan harus mendeteksi jumlah atom oksigen yang lepas dari belahan siang Venus dan memverifikasi bahwa jumlahnya sekitar setengah kali jumlah atom hidrogen yang lepas.

Sampai saat ini, ilmuwan belum menemukan tanda-tanda lepasnya atom oksigen dari belahan siang Venus. Penemuan ini juga membuka misteri baru lainnya. Hasil penemuan saat ini menunjukkan sedikitnya ada dua kali lebih banyak atom hidrogen di bagian atas atmosfer Venus dari yang ilmuwan perkirakan. Ioh hidrogen yang terdeteksi dapat berada di daerah (region) atmosfer bagian atas tetapi sumber terbentuknya daerah (region) ini masih belum diketahui.

Sumber : ESA Science: Where did Venus’s water go?

Article : Smallest Terrestrial Exoplanet Yet Detected

2009-02-04T06:43:00.003+07:00

COROT-exo-7b, bottom left dot shadows in front of his central star (artist's impression). Because of its proximity to large solar researchers suspect temperatures over 1000 degrees Celsius on the extrasolar planets. Image: Klaudia Einhorn.

The CoRoT satellite has found the smallest terrestrial exoplanet yet, — with a diameter just under twice that of Earth — complete with a rocky surface you could walk on and possibly even oceans to sail across. However, if you traveled there, you might want to bring some protection, as the temperature of this planet is likely very high. CoRoT-Exo-7b is located very close to its parent star, orbiting once every 20 hours. Astronomers estimate temperatures on the planet could be between 1000 and 1500°C and it possibly could be covered in lava or water vapor. This latest exoplanet was detected as it transited in front of its parent star, dimming the light from the star just enough to be noticeable.

The parent star lies about 140 parsecs from Earth, located about half way between the star Sirius in Canis Major and Betelgeuse, the red giant star in Orion.

The internal structure of CoRoT-exo-7b particularly puzzles scientists; they are unsure whether it is an ‘ocean planet’, a kind of planet whose existence has never been proved so far. In theory, such planets would initially be covered partially in ice and they would later drift towards their star, with the ice melting to cover it in liquid.

COROT detects small, transiting exoplanet. Credits: CNES

"This discovery is a very important step on the road to understanding the formation and evolution of our planet," said Malcolm Fridlund, ESA’s CoRoT Project Scientist. “For the first time, we have unambiguously detected a planet that is 'rocky' in the same sense as our own Earth. We now have to understand this object further to put it into context, and continue our search for smaller, more Earth-like objects with COROT," he added.

About 330 exoplanets have been discovered so far, most of which are gas giants like Jupiter and Neptune. The density of COROT-Exo-7b is still under investigation: it may be rocky like Earth and covered in liquid lava. It may also belong to a class of planets that are thought to be made up of water and rock in almost equal amounts. Given the high temperatures measured, the planet would be a very hot and humid place.

“Finding such a small planet was not a complete surprise”, said Daniel Rouan, researcher at the Observatoire de Paris Lesia, who coordinates the project with Alain Léger, from Institut d’Astrophysique Spatiale (Paris, France). “CoRoT-Exo-7b belongs to a class of objects whose existence had been predicted for some time. COROT was designed precisely in the hope of discovering some of these objects,” he added.

Small terrestrial planets are difficult to detect, and so very few exoplanets found so far have a mass comparable to Earth, Venus, Mars, and Mercury. Most of the methods used to find planets are indirect and sensitive to the mass of the planet. The CoRoT spacecraft can directly measure the size of a planet's surface, which is an advantage. In addition, its location in space allows for longer periods of uninterrupted observation than from ground.

Astronomers say this discovery is significant because recent measurements have indicated the existence of planets of small masses but their size remained undetermined until now. CoRoT (Convection Rotation and Transits) was launched in December 2006 and consists of a 27 cm-diameter telescope designed to detect tiny changes the brightness of nearby stars. The mission’s main objectives are to search for exoplanets and to study stellar interiors.

Source: ESA
Cited from : Universe Today by Nancy Atkinson