Wednesday, December 20, 2006

Signing off for the year

As my holiday travel nears and time to finish other things grows short, I'm signing off until after the start of the new year (unless something REALLY cool happens, in which case I'll be back on quickly). I thank all of you who are reading; in the past year, averade readership has tripled! For that, I am very grateful.

I wish you all happy holidays and a very good New Year, and I will start talking at you again in 2007!

Tuesday, December 19, 2006

The Holidays Cometh

Today the productivity of the astronomy department dropped markedly, as the coffee shop in our building closed up for the winter break. No more precious java will flow forth from the hallowed espresso machines until mid-January. So it is no wonder that most of the astronomers have left for the year.

Yours truly, however, is still plugging away, albeit in a caffeine-starved state. This evening, I was baking cookies while watching that holiday classic, "It's a Wonderful Life." And the opening of the movie contains some astronomy!

In the scene where the angels are speaking (Joseph, Franklin, and later Clarence), the angels are portrayed as galaxies. Not just any galaxies, but Stephan's Quintet, a tight grouping of five galaxies in the constellation Pegasus. Since, in reality, these five galaxies do not represent a meeting between two angels, what are we seeing?

A color picture of Stephan's Quintet was taken at Kitt Peak can be seen here. Note that four of the galaxies are a yellowish-white, and the fifth is almost pure white. The very white galaxy is much closer to us than the other galaxies; it just appears along the same line of sight. The yellow color is caused by the expansion of the Universe "redshifting" the galaxy light.

The four galaxies at the same distance are part of a "compact group." Galaxies, like people, tend to like to travel together in groups ranging in size from a few galaxies to many thousands of galaxies. Our own galaxy is in a group with the Andromeda Galaxy, the Triangulum Galaxy, and several small dwarf galaxies. The Local Group, as it is called, is pretty scattered. Andromeda is two million light-years away, and Triangulum is about three million light-years away. The Milky Way and Andromeda are each about 100 thousand light-years across. So there is a lot of room in our Local Group!

In Stephan's Quintet, on the other hand, the galaxies are very close together. Studies of pictures and spectra of the galaxies in Stephan's Quintet shows that there are two pairs of galaxies, and the galaxies in each pair are so close that gravity is pulling large streams of stars and gas out of each galaxy! We see interacting galaxies in many places, but having four bright interacting galaxies in such a small area of the sky makes this system interesting to study. Why are some groups of galaxies, like the Local Group, so spread apart, while others with similar numbers of galaxies, like Stephan's Quintet, so close together? In several billion years, the Local Group may look like Stephan's Quintet. The Milky Way will eventually collide with the Andromeda Galaxy, and the Triangulum Galaxy will probably collide with Andromeda, too. So, by studying this distant group, we can learn what might happen to our own galaxy in the distant future!

Monday, December 18, 2006

The wonders of the internet

I work with computers and on the internet every day, almost exclusively. This is true for most astronomers. So it is rare that I reflect upon how amazing what I am able to do really is. But today was one of those days where it hit me how crucial the internet is to modern astronomy.

When I got to work this morning, I had an email from the observers at the Hobby-Eberly Telescope, located at McDonald Observatory in west Texas. Over the weekend, they had taken some data for me. So, using the internet, I was able to download the data from 800 miles away. Here I had data, and I didn't have to drive 8 hours through the deserts and plains of Texas, nor did I have to stay up all night, nor did I have to worry about the weather. It was almost like magic.

Later this afternoon, I spoke via VoIP (voice over IP, or internet telephone), with a colleague in Australia, where it was Tuesday morning. I had briefly examined the data from the telescope and emailed him the results, and he wanted to chat about it. Even just a few years ago, it would have taken a couple of days to complete this exchange, by the time we sent emails to set up a time for a phone chat. And just 20 years ago the data would have had to travel by airmail. So, in a span of 8 hours, we managed to accomplish what would have taken days or weeks just a few years ago!

Of course, the downside is that people know when I am slacking (or at least they think they know). If I don't respond to email or answer an IM (instant message) though the computer says I am here, people know I am ignoring them. And sometimes a little sequestration away from the world is what I need to get work done, yet I get blamed for slacking. :) So, if you don't see me post for a few days, know that I am working hard to make the world safe for astronomy, even though I may really be playing games away from my desk for a few days.

Best Wishes!

One of my fellow postdocs here, Donna Pierce, is packing up this week to move to a faculty job at Mississippi State University for the start of the next semester.

I met Donna just a few months ago when I moved to Austin. She works on comets, quite a different topic from my work on distant galaxies! But she is a very friendly person nonetheless.

Good luck in Mississippi, Donna!

Friday, December 15, 2006

News from the Stardust Spacecraft

In this week's issue of Science magazine, the team behind NASA's Stardust mission reports their initial findings. Some of these have made the news in the last couple of days. Since the results are interesting, and since I have spoken with mission head Don Brownlee on several occassions, I thought I would blog a bit about that news today.

Stardust is a spacecraft that went through the cloud of dust around Comet Wild 2 ("Wild" is pronounced "Vilt") a few years ago. The spacecraft used a collector to pick up the dust and bring it back to Earth.

Comets are interesting to study because we know they formed in the outer parts of the solar system. Comets are full of ices that melt when close to the sun, so the comets had to form far out. We therefore expected to find that the comet was full of pristine material, "star dust" created by other stars that happened to be in the area when the comet formed.

But Stardust has found that the comet is not pristine. Yes, it has a lot of star dust, but it also has things that formed very close to the sun -- glasses and compounds that had to be made in a hot area. Some of these compounds are identical to the volcanic sands on the Big Island of Hawaii! And there is too much of this material to have been captured by the comet on previous trips past the sun.

We think that these findings show that the very early Solar System was a turbulent, violent place. Plumes of material from near the proto-sun were pushed out beyond the orbit of Pluto by processes we don't understand. And that took a lot of energy!

As is often the case, these findings raise more questions than answers. But it gives us plenty of new research to work on, so I won't complain!

Tuesday, December 12, 2006

Water on Mars?

At our daily afternoon coffee late last week, we were discussing the new images fromNASA's now-defunct Mars Global Surveyor. These pictures show changes in the gullies in a crater, suggesting that liquid water has flowed on the surface of Mars within the last few years! This would mean that Mars must have liquid water today in underground lakes or caverns, and that this water sometimes escapes to the surface, where it quickly evaporates.

Few of us here, and certainly not me, are planetary scientists, so it is hard for us to judge the data for ourselves. Must the changes in this crater be due to liquid water? I can't say. But it is fun to debate the implications. On Earth, liquid water = life. Did Mars ever have life? Could it have life now? Can living things survive in this water, which is probably very acidic and extremely salty? I don't know the answers to that, either. But it is fun to speculate! Now the question becomes how to find the water and search for life without contaminating Mars or a soil sample with bacteria from Earth. Easy enough to say, but hard to do! Do we need a lander that can traverse these craters? If the crater is full of dust, how can a lander safely land and get partway up the crater wall without slipping? How can we completely sterilize a spacecraft that, by necessity, must sit on the launch pad in Earth's weather and launch through Earth's atmosphere, which is teeming with all forms of life?

Friday, December 08, 2006

Last of the Spectra

Sorry I missed yesterday's posting, but I managed to break some software on my computer and spent a lot of time getting it working again. I shouldn't have believed those who told me it was an "easy" update I was trying to do!

Anyway, let's spend a last day with some of the neater spectra I have. Remember, just click on the spectrum to get a larger version of the picture. As a reminder, here is a spectrum of the sun:

.

Remember that all those narrow lines are "fingerprints" of the elements in the sun, such as iron, magnesium, calcium, and hydrogen. Now look at this next spectrum of a star-like object called BL Lacertae:

It has almost no lines at all! It took a long time to figure out that what we astronomers were seeing was a black hole. We are looking right down close to its event horizon, where things are so hot, individual elements don't show up in visible light! For another strange spectrum, look at this spectrum of the star T Tauri:

Here, if you look closely, you can see a spectrum that looks almost like that of the sun, but there are bright lines on top of it! Those bright lines have the fingerprint of hydrogen. What we see here is a very young star about the size of the sun, with some hydrogen gas still falling onto the star.

Lastly, let's look at my favorite of all of these, the spectrum of the Crab Nebula:

This spectrum is different from the rest. In the other spectra, I smeared out the light from the star up and down so you could see the lines better. Here, I am showing the spectrum "as is." The straight vertical lines here are the streetlights of San Jose, CA. (I took those out of the other images). The horizontal lines are spectra of stars that happened to be in the way. But the crooked, knotted vertical lines are the Crab Nebula itself. Most of the light here comes from hydrogen and oxygen. The crookedness is caused by the gas of the nebula moving very fast -- almost 1000 miles each second! The light is Doppler shifted, meaning its color changes depending on how fast it is moving. So, we astronomers can use this spectrum to figure out how fast different parts of the nebula are moving. The gas here is moving so fast because the Crab Nebula is what remains of a star that exploded nearly 1000 years ago!

Wednesday, December 06, 2006

More spectra

So, remember yesterday I said that the fingerprints of the elements that make up a star are visible in its spectrum. But what about the spectra of things in our solar system? Planets and moons don't make their own light, they just reflect sunlight. So you should expect the reflected light to have a spectrum identical to the sun.

For the most part, this is true. Below are three spectra. The first is of the sun, the second is of Saturn's moon Titan, and the third is of the planet Uranus. You can click on an image for a larger view.

Notice that Titan (the middle spectrum) looks a lot like the sun, with the exception of a little less blue light and a band of red light that is ever-so-slightly diminished. If you look at a color picture of Titan, you can see that it is yellowish -- the same color as the sun, but with less blue light.

The spectrum of Uranus, on the other hand, looks much different from the sun. Some colors are completely missing, and there is almost no red light! You are still seeing the spectrum of the sun, but the atmosphere of Uranus (mostly methane) has absorbed those "missing" colors of light. Once again, if you look at a color picture of Uranus, you'll see it is a greenish blue, the same as the colors of light left in its spectrum.

Tomorrow I'll finish up showing off my spectra with a few objects from outside the solar system.

Tuesday, December 05, 2006

Learning from the colors of the rainbow

One of the main tools astronomers use to determine what we are seeing through a telescope is a spectrum. A spectrum is a splitting of light into its component colors, just like a rainbow. The picture above shows a spectrum of the sun. If you look closely, you'll see several dark lines. These lines are caused by different materials in the sun, like hydrogen, iron,calcium , magnesium, carbon, oxygen, and so on. Each element has its own unique set on lines that appear in the spectrum, just like a fingerprint. Only in the astronomy, these fingerprints get stacked, one on top of the other, to make the pattern you see here.

Different objects have different spectra. Compare the spectrum of the sun (above) to the spectrum below this paragraph. Notice any differences? (You can click on the spectra to make the images larger.)

The two main differences are: the lower spectrum has many fewer lines, and also has much brighter blue and less obvious red. The star we are looking at (Algol, in the constellation Perseus) is a very hot star. The star appears blue in color (as you can see from the spectrum) and is so hot that the normal lines from metals like iron don't show up -- those metals have lost the electrons that make the characteristic lines!

Tomorrow I'll put up a few more fun examples. But the color representation is just to help you visualize the spectrum -- we astronomers don't use color pictures like this. Instead we make graphs showing how much light we get at each specific wavelength (or color), so that we can use mathematics to uncover even more details than the human eye could ever notice.

Thanks to John Kielkopf at the University of Louisville for writing the program that colorized these spectra!

Monday, December 04, 2006

Working against the clock

As an any profession, astronomy has its share of deadlines. One of the biggest deadlines are telescope proposals, where we request telescope time for the coming four or six months. For most ground-based telescopes, these are generally due in March and September (sometimes there is a third due date in the middle of summer, if an observatory works on a trimester system). For space-based telescopes, like the Hubble Space Telescope, these proposals are due once a year, typically in late January or early February.

I am applying for permanent jobs again this fall; many of those are due this time of year. I had four applications due on Friday and another one due this week, plus several more scattered between now and the end of January.

We also have deadlines when preparing to use the telescope. Some observations require metalsmiths to mill special masks with tiny slits wherever there is a star or galaxy we astronomers are interested in. These often take a month or more to make, and I have some due soon.

So, in short, I'm swamped and behind (as usual). So, if you don't hear much from me in the next few days, know that I am trying not to neglect you all.