belajar Astronomy

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?

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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

2009-04-24T15:15:00.000+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