Friday, September 29, 2006

Here come the Nobel prizes

Once yearly, the Nobel Foundation awards its prizes in physics, chemistry, medicine, literature and peace. (Other "Nobel" prizes, such as the prize in economics, were established in memory of Alfred Nobel, but are not part of Nobel's will.) Starting on Monday, the 2007 prizes will be announced, culminating with the Nobel Peace Prize on the 13th of October.

Who will win? I really don't know -- I can make some guesses for the physics prize, but they would almost certainly be wrong. However, when the prize in physics is announced, I'll see what I can do about explaining the research.

Also, October 5 will feature the awarding of the 2006 Ig Nobel Prizes from Improbable Research. Stay tuned for news from there, too!

Thursday, September 28, 2006

What went boom in the night?

Supernovae are some of the most energetic events in Universe. Most supernovae are thought to come from stars eight or more times more massive than the sun that have used up all of their nuclear fuel. Gravity causes the center of the star to collapse into a neutron star or a black hole, and the energy released by that collapse causes the star to blow itself apart.

There are many things about supernovae that we do not yet understand, and many of unknowns could be solved by looking at supernovae in our own galaxy. However, the last supernova seen in our galaxy was 402 years ago, on Oct. 9, 1604. Not very many living astronomers were around for that event, and the state-of-the-art observing tool (the eyeball) is primitive compared to today's instruments.

So, much of the work on supernova is done on explosions in distant galaxies, not in our own. The exceptions to this are studies of supernova remnants -- the shreds of gas that the explosions leave behind.

There are many such remnants, but for very few of them do we know the date when the star exploded. This is very useful, because knowing the time of the explosion allows us to study how these remnants evolve over time. Some famous supernova remnants are the Crab Nebula (seen by the Chinese in 1054), the supernova of 1572 (Seen by Danish astronomer Tycho Brahe), and the supernova of 1006, one of the brightest recorded supernova, being over 100 times brighter than the planet Venus!

From Chinese and Roman records, astronomers knew of a supernova that occurred in A.D. 185, but we weren't sure what, if any, remnant it left behind. Two supernova remnants are in the right general area of the sky, but astronomers guessed that these were many thousands of years old. Some astronomers even suggested that there was no supernova, but that the event was a bright comet.

Now the mystery appears to be solved. X-ray observations of one of the two suspect remnants, RCW 86, finds that it is not several thousand years old, but only a couple thousand years old, making it an almost perfect match to the observed supernova. How could we have had the age so wrong?

One way we get the age of a supernova remnant is to measure how fast it is growing and compare it with the remnant's size. For example, if it is 10 light-years across and growing at a rate of 0.01 light years per year, we know it is 1000 years old. But some parts of Supernova 185 seem to be plowing into dense clouds of dust and gas that are slowing it down faster than other parts, giving us errors in the derived age. The X-rays in the picture above allow us to see the dust and gas getting heated up by the expanding blast for the first time.

So, mystery solved, probably, and another supernova remnant with an age known to a few months.

Monday, September 25, 2006

Retrograde Motion

Today I had an email from a reader asking about retrograde motion of planets. The question is probably a homework question, so I didn't answer it outright, but sent some hints. But the question touches on one of the toughest concepts in astronomy -- understanding motion.

Everything in the universe is in constant motion relative to most everything else. But it doesn't feel like we are in motion. When you are in a car, plane or boat, you can "feel" the motion. On a motorcycle, you can feel the wind rushing past you. During an earthquake, you feel the ground moving under your feet.

But when you look up at the night sky, there is no feeling of motion. If you stand still for a long time, you might notice that the stars have moved a bit. If you look night after night, you might notice that, over time, the stars are in a slightly different place every night, and that some of the "stars" (actually planets) move with respect to the other "fixed" stars. But you certainly don't feel like you are spinning about Earth's axis at 700 miles per hour, or orbiting around the sun at 19 miles a second, or whizzing through the galaxy at 140 miles per second. You have to watch for an entire month to see the moon go around the Earth once. The sun takes a year to make a full circuit through the skies. This is hard to visualize!

In retrograde motion, a planet such as Mars stops its normal west to east motion through the skies and starts moving east to west for a few months before resuming its normal motion. Something happened, but what?

Mars didn't change directions in its orbit. The amount of energy that would be required to stop Mars, make it orbit backwards, and then switch directions again would be mind-boggling. It just doesn't happen.

On my move to Austin from Tucson, Arizona, I drove for several hundred miles along railroad tracks. At one point, I was passing a train, and I thought it was moving the opposite direction that I was -- it looked like it! But then I passed the front of the train, and saw it was moving east, like me. I was just moving somewhat faster than the train, and against distant mountains, it looked like the train was moving backwards.

The same thing happens with the retrograde motion of the planets. We all go the same direction around the sun, but the closer a planet is to the sun, the faster it moves. We take one year to orbit the sun, Mars takes almost two, Jupiter takes eleven. So, every couple of years, we catch up to Mars and pass it. And as we pass it, it appears to move "backward" with respect to the background stars. Once we are well past Mars, we get to a vantage point where we can see Mars's "real" motion again. The same thing happens with all planets further away from the sun than the Earth.

Confused? Probably. Just remember, we are moving through space, along with all the other planets; we just don't feel the motion. And that lack of perception of motion makes concepts like this all the harder to understand.

Friday, September 22, 2006

Welcome to fall!

Tonight, at 11:03pm Central Daylight Time, fall officially arrives for the northern hemisphere, and spring arrives for the southern hemisphere. At that instant, the apparent position of the sun in the sky crosses the equator, heading south for the winter (along with birds and many retirees).

Those of you who look at sunset/sunrise times may notice that today is not exactly twelve hours from sunrise to sunset, as you would think should happen, since the term "equinox" means equal night and equal day. This would be true if Earth didn't have an atmosphere, but our atmosphere bends light so that the sun appears to rise earlier and set later then it actually does.

By the way, the legend about being able to balance an egg on its pointy end only on the equinox is just a legend. With patience, you can do that trick any day of the year. And, if you don't want to be patient, trying to balance the egg on top of a tiny pile of salt or sugar will help you a lot.

Thursday, September 21, 2006

Freezing the atmosphere

As any observer will tell you, the atmosphere is a very messy thing. Even on nights that seem very calm and crystal clear, wind currents, temperature changes, and other structures in the atmosphere cause any image to blur. Many astronomers consider this blurring (or "seeing") to be acceptable if the size of the blurry spot made by a star is less than one-half to one arcsecond. (One arcsecond is 1/3600th of a degree, or the thickness of a small finishing nail seen from a mile away.)

During the day, the seeing is usually much worse than one arcsecond, as heating from the sun sets up currents in the atmosphere.

This is what makes the above picture so amazing. It was taken by Thierry Legault in Normandy, France, and shows the Space Shuttle Atlantis leaving the International Space Station and silhouetted against the sun. You can clearly see the shape of the space shuttle and the station, even though they were 550 kilometers (345 miles) away! I did a quick calculation, and I estimate that the width of the shuttle's cargo bay is about 2 arcseconds in this image, and yet you can see even sharper details!

Some astrophotographers now use video cameras to create sharp images. Although the atmosphere is constantly roiling, there are occasional, very short periods of very steady seeing, much better than an arcsecond. These astrophotographers look through thousands of frames of video for the handful that are crystal clear, and add these together to get a very sharp image.

Thierry Legault didn't have that option, though, because the space station only took a little over half a second to cross the sun. So, Legault just took some very short exposures (1/8000) of a second. Such a short exposure "freezes" the atmosphere, which changes on the order of every hundredth of a second. That, with a little patience, preparation and luck, and you get a nice clear picture of two objects 550 kilometers away.

Thierry Legault has several more very impressive pictures on this website.

Tuesday, September 19, 2006

UFO sighted near the space shuttle!

But, before you get too excited, the mystery object is NOT an alien spacecraft. (If it WERE an alien spacecraft, it wouldn't be an unidentified flying object, now, would it?)

Chances are good that the object is a piece of the Space Shuttle itself. Why? First, it appeared after the shuttle tested some propulsion rockets. Anything not tightly attached to the shuttle would then fly off on its own. But, unlike what you probably think, the rockets would not have "shaken" the object loose. Rather, when the rockets fire, the object will continue to follow the same orbit it had been on -- it is the shuttle that moves.

The other reason for thinking this is something from the shuttle is that the object is in almost exactly the same orbit as the space shuttle. The likelihood that this happened by chance is extraordinarily low. It would be like closing your eyes, spinning around, and throwing a rock as hard as you could, only to have it follow the same path as an airplane flying overhead. Both the rock and the airplane could be going in any direction; to have it be the same would be very rare. Plus, in the case of the UFO, it also has to match the height and speed of the space shuttle.

I think most likely this is some piece of a tool that the spacewalking astronauts didn't secure right, or maybe a piece of fabric from inside the shuttle's cargo bay that was ripped off during the installation of the space station's new solar panels.

To be on the safe side, NASA has delayed the shuttle's return for a day to make sure this object is not a piece of the shuttle's thermal tiles. I think that's a good idea.

Too bad it isn't an alien spacecraft, though. THAT would be exciting!

Monday, September 18, 2006

Finishing up another paper

Friday and today I have been making edits to a paper I am about ready to submit. It is a paper presenting most of the work from my doctoral dissertation, which will finally be published four years after I earned my degree.

Despite having published several papers, I am always surprised at how long one particular aspect takes -- making figures and graphs. For some of my papers, a picture is worth more than a thousand words, as it can contain information about tens of thousands of stars. For that reason, I am a bit anal about my figures. Friday I spent the entire day on a single figure that STILL isn't done to my satisfaction, though it is close.

Not only do we need to convey information, but we have to worry about some silly details. The journals will only publish color figures at a high cost and with extra editing steps, so I work to make all of my figures grayscale or black and white. Also, the journal takes a full-page figure and shrinks it down to about 1/8 of a page, so I have to make sure my plots are still legible when they are reduced. And, now that most astronomers use Powerpoint to give research talks, I need to make sure that my figures will also look nice when pulled into the lower-resolution Powerpoint presentations.

Hopefully today I can finish that figure...

Saturday, September 16, 2006

Astronomy and the American pastime

Last night I went to the Dell Diamond ballpark to watch the Tucson Sidewinders defeat the Round Rock (Austin) Express to win minor league baseball's Pacific Coast League Championship. The Sidewinders now advance to the minor league version of the World Series, playing the winner of the International League Championship.

Although I now live in Austin, I was rooting for the Sidewinders, as I've gotten to watch them quite a bit in the last few years. Next year, I promise to root for the Express.

I did have a bit of an astronomy experience. At the game, I sat next to two college kids who came to watch the game. One, semi-obnoxious kid was from El Paso and rooting quite loudly for Tucson. The other was a local guy rooting for the Express. I was chatting with the latter gentleman, who mentioned that he had just had a dream the previous night about going to the observatory.

Coincidence? Yes, absolutely. But it gave an opening to chat for a little bit about what I do, in between pitches. I always like those easy openings.

Anyway, congrats to the Sidewinders, and have a good weekend!

Wednesday, September 13, 2006

Do our astronauts have a screw loose?

I must admit, I am a bit surprised how much news is made out of an astronaut losing a screw and bolt. Just imagine you are in the middle of the ocean wearing a few pairs of winter gloves and trying to tighten bolts. I bet most of us would lose more than one. I'd be lucky to retain any.

My October issue of Scientific American arrived today, and the cover story is on supernovae (exploding stars). I'm looking forward to reading that. Scientific American is, in my opinion, one of the best science magazines available, so you may want to give it a look. However, it does run a bit on the dense side, so there's no need to be ashamed if you can't follow it. I often have to give up on the biology articles, as I get lost after the first page or so.

Sorry to be a bit scatterbrained today, but I'm helping some collaborators get started on a telescope run, and I am short on sleep to boot.

Tuesday, September 12, 2006

Is the Big Bang in trouble?

Yesterday, Space.com posted this article, claiming that a new scientific study may call the Big Bang into question. Is this true?

The Big Bang is the most successful theory proposed for the creation and evolution of the Universe. The theory was developed after Edwin Hubble observed that almost every galaxy in the Universe is moving away from every other galaxy, now understood as the expansion of the Universe. The theory has made some remarkable predictions that were shown to be true, such as the cosmic microwave background ("echoes" of the Big Bang visible in radio waves) and the ratio of hydrogen to helium in the Universe, to name a couple. Tweaks to the Big Bang (such as the theory of Inflation) made other predictions that have been shown to be true, such as the shape of the Universe and the small variations in the cosmic microwave background. So the Big Bang theory is amazingly successful, and it would take very compelling data to cause most scientists to question it.

The study looked for shadows of clusters of galaxies on the microwave background -- extremely hot gas in the galaxy clusters should distort the wavelengths of the radio waves from the Big Bang. However, the study on Space.com found much weaker shadows from many galaxy clusters than theory would predict. The study's authors state that the most likely explanation is that we don't understand the galaxy clusters as well as we thought, and this seems a quite reasonable explanation. However, one other explanation is that we don't understand the cosmic microwave background as well as we thought, which would throw the Big Bang into question.

Given the mountain of evidence supporting the Big Bang and the likelihood that we don't understand clusters of galaxies, the study's authors (and yours truly) feel that the Big Bang is quite safe. But we must be honest and admit that there is a tiny, tiny chance that the Big Bang theory may be incomplete or incorrect.

But does such a small chance warrant a large article under the "Cosmic Mysteries" section of a media outlet? Probably not. Such stories create tempests in a teacup that mislead members of the public into thinking the Big Bang is more controversial than it actually is. Of course, the media have ever right to pick up on this story, and I certainly won't write Space.com and argue that such stories should not be printed.

More importantly, this is a warning to you, the member of the public. When you read that one scientific study or another challenges a major theory, be skeptical. More often than not, any controversy is overblown, and most of the rest of the time, the research is of questionable quality. And always feel free to ask a professional for the real skinny!

Friday, September 08, 2006

What is the largest planet?

Lost in the debate over the (dwarf) planet Pluto's status in our solar system is perhaps a more important debate: What is the largest object that can be called a planet around another star?

For objects about 13 times the mass of Jupiter, deuterium (a heavy form of hydrogen) will burn in a nuclear reaction, though once the deuterium is burned up, all nuclear reactions stop. For that reason, most astronomers are comfortable calling objects this big "brown dwarfs," the term for wannabe stars.

What about for smaller objects? Gigantic planets can form in two ways. They can form like the giant planets in our solar system -- a disk of gas and dust around the parent star forms small asteroid-like objects that collide due to gravity to make larger and larger bodies. Once these are several times the mass of the Earth, their gravity is strong enough to scoop up gas, too, and the planets rapidly grow to hundreds of times the mass of the Earth, just like Jupiter and Saturn.

The other method is that, as the parent star forms out of a big cloud of gas, a hunk of that gas splits off and collapses on its own to form something 10 times larger than Jupiter. The only difference between a planet 10 times the mass of Jupiter formed this way and ten times the mass of Jupiter formed the other way is that the latter will have a rocky core several times the mass of the Earth, while the former will be all gas. From the outside, though, it is nearly impossible to tell the difference.

Today NASA announced the discovery of a brown dwarf about 12 times the mass of Jupiter around a nearby star. One of the co-discoverers, Kevin Luhman, a professor at Penn State, claims that this object must be a brown dwarf and not a planet because it is far enough away from the parent star that there could not have been a disk of dust and gas to form the object.

The problem is that, for many objects from about 10 times the size of Jupiter to 13 times the size of Jupiter, it is unclear which process formed the planet/brown dwarf. So, what are these objects to be called? Are they a fallen star or a risen planet? Like the case with Pluto, I don't know that there is a single answer that everyone will find satisfactory. My guess is that, eventually, we astronomers will tire of the controversy and call these something like "transition objects" or some other suitably vague term. Then we can stop arguing about what to call them and start arguing about true scientific topics -- how these things form, how they change with time, how common they are. And these topics may provide us with hints as to whether one formation scenario is favored, or if both seem to come in to play. And from that, we learn more about how stars and planets form.

Thursday, September 07, 2006

Settling in

Moving to a new place is not much fun, but I think I am just about settled in. A couple of pieces of new furniture arrive today, and my home newspaper and internet should start next week. That will make for a good start.

Meanwhile, astronomy keeps marching on in spite of my absence. I am trying to catch up on reading scientific articles that have appeared in the last few weeks, collaborators are bugging me for information, and later this month it will be time for telescope proposals to be submitted. Plus, it is about time to start applying for jobs again (even though I am not yet settled!).

As part of my new position, I will be making some changes/improvements to this blog in the coming month or two, and I'll be asking for input along the way. So, there is much to do in little time. I guess I'd better get busy!

Tuesday, September 05, 2006

Landing in a new city

My move from Arizona to the great state of Texas is going fairly smoothly. I arrived late last week, as did the moving truck with all of my junk. So, today I decided to tackle the bureaucracy at the University of Texas. Getting my office was easy, as was an email account and an employee ID card. Parking will be harder. And harder yet is catching up on email. Collaborators have questions about upcoming telescope runs, I have a few papers I need to submit comments on, and I need to restart my research and write more papers. So my work is cut out for me!

See, life as an astronomer isn't all fame and fortune. Actually, it's very little of either, and moving certainly detracts from the fun of the job. But we'll see where things go in the next few weeks!