Wednesday, December 16, 2009

Astrofotografi - The Atmosphere and Observing

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.

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


Tuesday, December 15, 2009

Gerhana Bulan di Malam Tahun Baru

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

Sunday, December 13, 2009

Hujan Meteor Geminid di Penghujung Tahun 2009

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.


Monday, December 7, 2009

Mengenal Objek Langit

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.

Sunday, December 6, 2009

Basic Astronomy: Phases of The Moon

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:

  1. 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.
  2. 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.
  3. 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.
  4. Waxing Gibbous – This phase of the Moon occurs when the Moon is more illuminated that half, but it's not yet a full Moon.
  5. 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.
  6. Waning Gibbous – In this lunar phase, the Moon is less than fully illuminated, but more than half.
  7. 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).
  8. 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

Saturday, December 5, 2009

How Galaxies Lose Their Gas

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

Tuesday, December 1, 2009

2012 Doomsday Hoax

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

Wednesday, November 25, 2009

The Extremely Large Telescope

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

Tuesday, November 24, 2009

Soal OSN Astronomi 2009 - Essay Teori

  1. 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.
  2. 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?
  3. Angin matahari yang isotropik (sama ke segala arah) menyebabkan laju kehilangan massa matahari 3×10-14 MMatahari 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?
  4. 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?
  5. 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:
  1. Jawaban nomor 1
  2. Jawaban nomor 2
  3. Jawaban nomor 3
  4. Jawaban nomor 4
  5. Jawaban nomor 5

Monday, November 23, 2009

More on Leonid Meteor Shower 2009

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?

Thursday, November 19, 2009

Leonid Meteor Shower 2009

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

Friday, November 13, 2009

Black Dwarf

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

Thursday, November 12, 2009

Sun's Lithium Mistery

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

Friday, October 30, 2009

Soal-soal Latihan

Beberapa soal astronomi sebagai bahan latihan dan diskusi dengan teman2:

  1. If the Earth rotated in the opposite sense (clockwise rather than counterclockwise), how long would the solar day be?
  2. 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?
  3. 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.
  4. If a planet always keeps the same side towards the Sun, how many sidereal days are in a year on that planet?
  5. If on a given day, the night is 24 hours long at the North Pole, how long is the night at the South Pole?
  6. On what day of the year are the nights longest at the equator?
  7. 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.
  8. 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?
  9. 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

GRB 090423
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 (Nasa)
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."

Artist's impression of GRB production (ESO)
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."

Italian National Telescope Galileo (TNG)
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

Friday, September 4, 2009

James Webb Space Telescope

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.

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.

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

Thursday, September 3, 2009

Astronomers Find Most Distant Supermassive Black Hole Yet

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

Tuesday, August 18, 2009

Mars, methane and mysteries

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

Sunday, August 16, 2009

Astronomer Found Planetary Nebula Around Heavy Stars

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

Thursday, August 13, 2009

Hubble Ultra Deep Field in 3-D

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.

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
  1. High rates of star formation during the very early stages of galaxy formation, under a billion years after the Big Bang.
  2. Improved characterization of the distribution of galaxies, their numbers, sizes and luminosities at different epochs, allowing investigation into the evolution of galaxies.
  3. 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.

Wednesday, June 17, 2009

Soal Latihan Astrofisika

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

Soal Latihan Astrofisika - 15 Juni 2009

Selamat belajar.

Monday, June 15, 2009

First Extra-Galactic Planet Spotted in Andromeda

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

Berikut ini ditampilkan beberapa soal "kelas berat". Silakan dicoba dan didiskusikan dengan teman atau guru di sekolah Anda.
  1. 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.
  2. 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).
  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
  4. 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.
  5. 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

Saturday, May 30, 2009

Resensi Buku : Menjelajah Tata Surya

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 :

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.