Thursday, July 31, 2008

Total eclipse of the heart sun

A partial solar eclipse in  1999
Image Credit: Yours truly

Tomorrow (1 August 2008), the moon will pass completely in front of the sun, at least in certain parts of the world. This map shows where the total eclipse will be visible (shaded dark blue area), and where the sun will be partly eclipsed by the moon (between light blue lines).

Total solar eclipses are rare, happening, on average, about every 18 months. And then notice how small of a portion of the Earth gets to see an eclipse -- a thin strip less than 100 miles wide, though a few thousand miles long. No wonder that any given part of the Earth will only see a total solar eclipse every 375 years or so! If you want to see a total eclipse, you'll probably have to travel, and this year that would involve going to Siberia, Mongolia, or China.

Rather than bore you with statistics about eclipses, or try to explain the geometry, I'll tell you my total eclipse story. It's a tale full of adventure, discovery, loss, love, and supernatural creatures. Okay, that's a lie. It's kinda boring. But it's true, and it's my story, so I'm sticking to it.

On August 11, 1999, a total eclipse of the sun was visible across Europe, including several major cities. I had lived in Munich, Germany in 1997, and Munich was in the path of the eclipse, so I figured that I would use the eclipse as an excuse to go and visit friends. Besides, total solar eclipses are supposed to be spectacular, and worth the cost of travel.

When I arrived in Munich a few days prior to the eclipse, telescope in tow, my plan was to go to the gardens of Castle Oberschleissheim, just outside of Munich, and hopefully away from most of the crowds that would fill the streets to try and see the eclipse. But the weather forecast was bad, with the news suggesting that one travel as far east or as far west as possible to have the best chance of seeing the eclipse.

I wanted to go east, into Hungary, but the dear friend I was staying with didn't want to go to Hungary, as it involved overnight train trips each direction, and neither of us spoke Hungarian. I was willing to risk it, but was not persuasive enough. So, we headed west to the city of Saarbrucken, which is on the border of Germany and France. The train was crowded, and I had my telescope in tow, which upset people, because it took up "too much" space (but, really, it is a small, but well-built, telescope)

For whatever reason, Saarbrucken and the French town of Forbach sent us eclipse watchers to a hill right on the border (I don't remember if the hill was officially in France or in Germany, but I know we crossed the border at least once). We rode buses from the train station to a walking trail that lead up to the hill. The German government had done a great job of explaining the dangers of looking at the sun without proper eye protection (even when the sun is 99% eclipsed, it will still permanently damage your eyes, even though it doesn't hurt to look at the sun). So numerous people told me that I shouldn't use my telescope. I had a very expensive and completely safe solar filter for the telescope, so we were okay using it. But one man in particular became almost belligerent, and I blurted out "Ich bin Astronom; ich weiss, was ich tue." (I'm an astronomer; I know what I'm doing.) Not quite as elegant as Bill Murray's line from Ghostbusters, "Back off man, I'm a scientist." But it had the same effect, and we were left alone.

On the hill outside Saarbrucken, the weather was okay. There were a few clouds, but the sun was out. I set up the telescope, and the eclipse began right on schedule! I hooked up a camera that I'd borrowed from my uncle to my telescope, and I took pictures (like the one above). All was fine until the sun was about 2/3 eclipsed. Then the thunderstorm came.

The sky clouded over, lightning danced around, and we were huddling under trees on top of a hill (dumb!!). I left my telescope set up, but my friend and I took turns holding the umbrella over it to keep it dry. And the rain poured down. The rain finally stopped a few minutes before the sun was to be totally eclipsed, but the sky was still overcast.

Right when the moon was to have totally covered the sun, the sky grew fairly (but not completely) dark in a period of just a few seconds, like someone had turned a dimmer switch down on an electric light. 129 seconds later, the lights came back up. It was still cloudy. We'd missed it.

Still, a few champagne corks popped, and the several hundred of us on the hill top started the long, wet slog back to town. We were soaked. But my telescope was dry, and I had some good pictures of the partial phases of the eclipse. We crammed onto a train and rode back to Munich.

Once back, we learned that Munich had also been cloudy, except during totality, which is the spectacular phase of the eclipse. So people in Munich got to see the best part of the show. And it had been even clearer up at Oberschleissheim, where I'd planned to be. So, if we'd stayed put, we would have seen most of the eclipse. AND, in Hungary, it was perfectly clear for the entire eclipse. Doh!

Still, I had a nice visit with friends, and I stoically accepted the weather. I was luckier than two of my friends who'd seen the eclipse in Turkey, but were then caught in the aftermath of the tragic Izmit earthquake just one week later. (My friends were lucky to have been out of the quake zone, but their return was complicated by the temblor.)

Someday I will catch a total solar eclipse. And, after that, I'll probably catch many more. I've been told that, once you've seen totality, you have to keep going back, even if it means taking a yak to the middle of the Altai Mountains.

For those of you in the United States who don't want to travel to exotic locations, you have to wait another 9 years for a total eclipse. The continental U.S. has been unlucky in eclipses; the last total eclipse in the lower 48 was in 1979, and the next one won't be until August 21, 2017. That eclipse will be spectacular for us Yanks, as it cuts a path clear across the country, from Oregon through South Carolina.

If you'd like to read more about both solar and lunar eclipses and see when and where future eclipses will be visible, check out NASA's Eclipse website.

Wednesday, July 30, 2008

Happy 50th Birthday NASA

Hubble wishes NASA a happy birthday

Today I learned that yesterday was the 50th anniversary of NASA's founding, though they'll celebrate again later in the year with much more fanfare. On July 29, 1958, President Eisenhower signed the bill creating NASA into law; NASA formally came into being on October 1, 1958. In less than 11 years, NASA sent the first humans to the moon. In 50 years, NASA has sent probes to every planet in the solar system, launched multiple space telescopes, built two space stations, and much, much more.

When you think about it, our attitude toward space has changed drastically in that short span. In 1958, people argued over if humans could survive in space, or if it were even possible to send rockets to the moon. These days, we argue about whether to send humans to Mars, but the argument is over the cost, not over whether it is possible. Things we take for granted, like satellite communication and navigation, were only dreamed of (if even that!) 50 short years ago. How times have changed!

Au revoir, Agnes

One of the depressing things about summer time as a young astronomer is that it means many of your friends pack up and leave as they advance in their careers. Earlier this summer, two of my fellow postdocs pulled up stakes for greener pastures. And yesterday, we said goodbye to another of our friends, as postdoc Agnes Kim and her husband Ryan left Texas for Milledgeville, Georgia, where Agnes will be a professor in the Chemistry and Physics Department at Georgia College and State University.

Agnes studies white dwarfs, like myself. She works on how white dwarfs might be useful for probing exotic particle physics, like the production of elusive neutrinos, or perhaps even the interaction of dark matter with the normal matter that makes up a white dwarf.

I wish Agnes and Ryan well in their new adventures!

Tuesday, July 29, 2008

The science of conflicting results

One of the things about science that tends to get the public most frustrated are conflicting results. As a fictional example, one day you might read a story about how eating sharp cheddar cheese can prevent stomach ulcers and reduce your cholesterol. Then a month later, after adding copious amounts of sharp cheddar to your diet, you read that another group claims that sharp cheddar cheese may help with ulcers, but does nothing for cholesterol. And another two months later, you might read that the sharp cheddar worsens both ulcers and cholesterol. And yet later you read that, no, cheddar is fine after all.

In astronomy, one of the places this often pops up is with water on Mars. One month you can read that Mars used to have a lot of water and was once suitable for life, another month you'll read that it had a little water that was highly unsuitable for life, and another time you'll read that Mars never had much water and has always been a barren planet. Arrgh!

I saw another clear example over the last two nights. I was watching Shark Week on the Discovery Channel. On Sunday, I saw a Mythbusters episode that examined many shark myths. Two myths they claimed to confirm were that (a) flashlights attract sharks, and (b) thrashing in the water attracts more sharks than playing dead. Then, last night, I saw the overly-dramatic "Surviving Sharks" episode, which found that (a) reef sharks are repelled by bright lights at night, and (b) playing dead is more likely to get you eaten than thrashing about. What gives?

As frustrating as it may seem, in all cases like this you are seeing science at work. Science is so much more than running a study and seeing the result. It also involved making sure that the experiment is properly designed, replicating results with a similar experiment, and replicating results with a different experiment. And these processes take time and effort from many groups, who often disagree (sometimes quite vocally). The science-savvy person has to learn some patience, in the belief that time will tell us what the real conclusions are.

When conclusions disagree, it can indicate many things. Maybe an experiment was not properly designed. Or maybe some factor that the experimenters did not control is important in determining the result. For example, in many medical studies, disagreements arise over the size of a study (the number of people looked at) and the makeup of a sample. Perhaps the fictional experiment that finds that eating copious quantities of cheddar cheese lowers you cholesterol is flawed, because a higher fraction of the people in that study exercise regularly.

In the case of Mars, many of the disagreements arise over soil chemistry. On Earth, there are many minerals in rocks that are known to form in the presence of water; since water is and always has been abundant on Earth, we assume those minerals are formed in water. But does that translate to Mars? Are there ways to make certain minerals without an abundance of water? Could just a humid day have the same effect? In some cases the answer is yes, in some cases the answer is no, and in some cases, we don't know. Similar arguments rage over whether water is needed to carve certain land features on Mars, or whether wind, lava, and even liquid carbon dioxide could do the same thing. These are the boundaries of Mars science. Mistakes will be made, hypotheses formed and rejected, and results of space missions debated for years to come until one idea proves itself to stand up against all challenges.

As for the sharks, there are some obvious differences in the experiments that could explain the contradictory results. If you get a chance to see both the Mythbusters and Surviving Sharks, take a close look and try and figure out what the differences are that may matter. What about both experiments are the same? What is different? Can you think of ways of improving the experiments to control more of the variables?

These are also questions you can ask yourself whenever you see conflicting science results. A lot of time you don't get enough information in a news article to answer such questions. But rest assured that other scientists are looking into these issues.

Monday, July 28, 2008

Sharks and Supernovae and Black Holes

So, this week is Shark Week on the Discovery Channel. It's the 20th anniversary of Shark Week, and the ratings will undoubtedly go way up this week. Clearly the public likes something about sharks -- one can hardly imagine that Discovery Channel would get nearly as high of ratings for "Mosquito Week," despite the fact that mosquitoes kill more humans each year than sharks ever have. And you can bet ratings would plummet on "Sloth Week."

When a person learns that I am an astronomer, there are three topics that tend to come up: black holes, supernovae (exploding stars of all kinds, really), and aliens (preferably ray-gun wielding invaders, not microbial mats lazing around an extraterrestrial deep-sea vent). I work on white dwarfs, which register pretty low on the excitement meter. At least it isn't the interstellar medium (the gas between stars, which gets some pretty pictures, but also a lot of rude jokes, and even more yawns when you try to explain the importance of identifying the various carbon chains responsible for PAH emission).

There must be something in our humanity that makes us interested in dangerous things. In paleontology, people like dinosaurs or saber-toothed tigers, not trilobites or Hyracotherium. In geology, people are far more interested in volcanoes than in silt-deposition rates.

But science is very inter-connected. Those boring silt-deposition rates are important to connecting the extinction of T. rex with the asteroid impact that sealed the dinosaurs' fate. And getting to understand those boring PAHs is likely crucial to understanding where any aliens (or humans, for that matter) came from. And protecting endangered shark species may well require understanding some of the smallest creatures in the sea.

I think it is great that so many different sciences, be it astronomy or ichthyology, have fields that can capture the curiosity of the human mind. And I'm cool with the fact that my own research may not be quite so captivating, as long as we all remember that science is interconnected, and today's boring drivel may be a crucial piece of knowledge to unlocking the mysteries of the most exciting areas of science.

Friday, July 25, 2008

Sometimes we miss the obvious

A couple of days ago, I wrote a long spiel about the nova nobody saw, despite the fact that it should have been visible to the naked eye. Reasons I suggested for why people may have missed it included that the constellation is near the Milky Way, so rich in stars (true), that the southern hemisphere has fewer amateur astronomers (also true), and that the sky is big and we may be missing a lot of novae (yet again, true).

But I may have missed the most obvious reason: the time of year. Robotic telescopes pinpointed the date of the explosion as June 5. What I didn't recognize at the time is that the constellation Puppis is near Canis Major (the big dog), which is a winter constellation. (This hit me when I read the Wikipedia article on Puppis).

On June 5, at twilight in the southern hemisphere (specifically, I refer to -29 latitude, where the Las Campanas Observatory is located), the nova was 40 degrees above the horizon, and setting fast. Within two hours, it would have been lost in the murky skies.

Now, in the southern hemisphere, it was winter. Think about your normal winter schedule. It gets dark early; often you aren't home from work yet at sunset, and it has been dark a couple of hours by the time you've gotten home, had dinner, and have time to relax. I suspect that the same is true of all but the most dedicated amateur astronomers. By the time they got outside and set up for viewing, the nova would have set. Also, remember the nights are long (and colder) in winter, and in the later half of the night, the riches of the center of the Milky Way would have been high in the sky for prime viewing. And the center of the Milky Way is more likely to have novae than the region where Puppis is found.

So, I'd be willing to bet that, even among the best southern hemisphere amateur astronomers, not that many were "on duty" before the nova set. So, it is even less surprising that the nova was only seen by a robotic telescope, which would have no family duties to worry about.

From the northern hemisphere, the nova (which would just barely be visible in best viewing) disappeared below the horizon hours before sunset.

So, in short, everyone had a good excuse to miss the nova; I'm not so sure I had as good of an excuse for missing this obvious explanation. And I suspect misses due to sunlight are much more common than anyone would care to admit.

Thursday, July 24, 2008

I could've told them this

A new study from researchers at the University of Wisconsin has revealed a very unsurprising result -- that women are just as good at math as men.

For my entire educational career, I've known many women who have been excellent math and science scholars, and many men who are not. Yet there still is a pervasive attitude in our society that science, math and technology are areas for men and boys to explore, not women. How pervasive is this attitude? If you go to an elementary school class and ask them to draw what they think an astronomer looks like, the vast majority of kids will draw a male astronomer.

Yet roughly one-quarter of all astronomers are female (source: Pasadena Recommendations from the Committee on the Status of Women in Astronomy), though this number is, in and of itself, unacceptably low. Gender inequality still exists in astronomy hiring and advancement, but this is not due to a lack of skills or ability -- it's due to lingering cultural issues.

It's a shame that studies like the University of Wisconsin study are needed to show that there is no gap in ability. It is a shame that our society still continues to imply that science and technology are not appropriate for women. It's time to move on and to avoid teaching our kids these stereotypes. Alas, that's easier said than done.

Tuesday, July 22, 2008

The no-view nova

X-ray image of the nova nobody saw
Image Credit: Contours: ESA/ XMM-Newton/ EPIC (adapted from A. Read et al.), Background: SSS

Most of the time, the stars and galaxies that we astronomers look do not change much, if at all, over a human lifetime. So, our only hurry in looking at a star is to do it before somebody else does. If the weather is bad or the telescope breaks, we can come back another night, or even another year, and there is little lost.

For some astronomical objects, though, time is critical. Supernova explosions, for example, are only visible for a few months or so before fading away from sight. Another, more common explosion, called a nova, only lasts a few nights. Glows from gamma-ray bursts last just a few hours. If one of these events occurs, we need to hop on it fast, or lose it forever.

The problem is, you've got to be looking in the right place at the right time to see one of these. At present, there are only a few small telescopes that take pictures of the entire sky on a regular basis. Such a search produces tremendous amounts of data, and on big telescopes, the biggest cameras can only image about one quarter of one ten thousandth of the entire sky in a single picture. So, much of the sky is not searched by professional astronomers for these time-critical events. Those who do search for these events tend to focus on tiny patches of the sky. Though they'll miss most explosions, they'll still see enough for their science. (The one exception are gamma ray bursts, because the gamma ray detectors in space actually can look at most of the sky in a single picture.)

Typically, this is where amateur astronomers step in. These men and women are often out conducting searches of their own, often using their own eyes and star charts to try and spot something out of place. It may be a comet, or it may be an explosion, or it could be some other event. Amateurs are pretty good at this, and are discovering comets, supernovae and novae all the time. They get a little bit of glory, and a lot of personal pride, out of beating us professionals. And they deserve it.

One of the big prizes is discovering something that will become bright enough to see with the naked eye (i.e., without a telescope or binoculars). Then people around the world will be able to go out and see your discovery, sometimes with your name attached (like Comet Hale-Bopp).

Still, even a small army of amateurs can't catch everything. This was proven in a press release last Friday from the European Space Agency's XMM-Newton X-ray telescope.

The X-ray telescope, like an optical telescope, points at interesting targets and takes pictures. When it moves from one target to another (which takes a long time in space), the cameras are usually turned off. But a group of scientists including Andy Read of the University of Leicester and Richard Saxton of the European Space Agency are running a project where, sometimes, the cameras are kept running as the telescope moves, allowing random objects to drift into the field of view.

Last October, a bright X-ray source popped into the XMM-Newton camera during one of these moves, but, according to catalogs, nothing should have been there. After some quick legwork and a few phone calls to big telescopes, it was determined that the X-rays were coming from a previously unknown nova.

A nova is a distant cousin of a supernova. In a supernova, an entire star explodes during a runaway nuclear explosion. In a nova, the outer layers of a white dwarf star explode like a hydrogen bomb, but the explosion is too weak to blow the entire star apart. As you might guess from the names, a supernova is many times brighter than a nova. But novae are actually more common, because there are a lot of white dwarfs in our galaxy. Several novae are found every year, and every few years, one is bright enough to see with the naked eye. As with bright comets, most novae are found by amateur astronomers, and not by professionals.

The odd thing about the XMM-Newton's discovery, though, is that novae don't make a lot of X-rays early on. So, the nova that XMM-Newton found was actually a few months old, but it had never been reported. So, the XMM-Newton team called up the operators of a robotic all-sky survey called ASAS. They combed through old data, and found that the nova had indeed been picked up by their optical telescopes on June 5, 2007. Not only that, but the nova had gotten bright enough that it would have been easily visible to the naked eye, the brightest nova in over a decade. And yet, not one human knowingly saw it!

How did everyone miss it? Well, the nova was in the constellation Puppis, which is not visible in most of the northern hemisphere (where most amateur astronomers live). And Puppis lies near the Milky Way, so it is full of stars -- only a trained eye would have been able to pick out the new one. But novae are found in Puppis by professional and amateur astronomers quite a bit. We just got unlucky with this one.

Discoveries like this make us wonder how many interesting things happen in the sky on time scales so short that nobody has a chance to see them. For that reason, astronomers are starting to build telescopes that will image the entire sky to very faint limits every few days. The ultimate data will come from the Large Synoptic Survey Telescope or LSST, which will soon be built in Chile. The mirror for this telescope is huge -- 8 meters across, making it one of the largest telescopes in the world. The telescope, in a single picture, can image an area of sky about 50 times the area of the full moon. A single 30 second exposure will be able to see objects about 2 million times fainter than what your eye can see.

Amazingly, the hard part of this project is not the telescope (though it will be one of the most complex mirrors and cameras ever built). The hard part will be the data volume: 30 terabytes of data every night. That's 30,000 gigabytes, or, if you were to put it on a normal DVD, about 6000 DVDs worth of information every single night. For five years. And we want to be able to analyze that data on the fly, so that interesting objects (like novae) can be observed with other instruments at other telescopes as soon as possible. To help with this, money and assistance from Google and the Bill and Melinda Gates Foundation (along with other technologically-oriented companies) are pouring into the project.

The LSST mirror is under construction in Tucson, Arizona, and the construction will soon start in Chile, with hopes of opening this new eye on the Universe in 2014. Hopefully no more novae will slip through the cracks!

Monday, July 21, 2008

39 years ago today...

Buzz Aldrin poses during Apollo 11
Image Credit: NASA

39 years ago, humankind took its first tentative steps into the cosmos when astronauts Neil Armstrong and Edwin "Buzz" Aldrin walked on the surface of the Moon as part of the Apollo 11 mission. (Their moonwalk, while only 2.5 hours long, started about 11pm EDT on July 20 and finished in the early morning of July 21, so there is some ambiguity in the "date" of the moonwalk. But why not celebrate this amazing accomplishment over two days, instead of just one?)

At the end of the Apollo Moon program in December, 1972 (a full year before I was born), few people suspected that it would be nearly 50 years before we returned to the moon (and it could be longer than that, if the Orion project is significantly delayed). To some people, this is a travesty. Other people wonder why we are even considering going back.

I think it is in our nature to explore. From our early Homo sapien ancestors leaving the African continent to colonize new lands, to seafaring peoples of many nations and races that sailed the vast and unfriendly seas, to the astronauts/cosmonauts/taikonauts who risk their lives to sail the vacuum of space, the unknown seems to draw us onward. So, I suspect that it is just a matter of time before we humans are crawling across the face of Mars, and perhaps even considering one-way flights to explore new worlds around other stars. But this "time" may be hundreds or thousands of years from now, and there are many other challenges facing us right here on our home planet. So I think we can afford to be patient, as long as we don't take our eyes off the ultimate goal.

Sp, if you look out late this evening to see a big yellow moon rising, remember that we were there just 39 short years ago.

Friday, July 18, 2008

One really cool movie

Credit: D. Linder / EPOXI / NASA

The video above shows a very unique view of the Earth/moon system. It was taken by the EPOXI Mission, the name of NASA's Deep Impact spacecraft's new mission (now that it's completed its mission to explore Comet Tempel 1). The spacecraft turned its onboard camera toward the Earth in late May when it was 31 million miles away from Earth, and it captured (intentionally) the Moon passing in front of the Earth.

The video above is roughly true color. A cartoon globe in the lower left shows you what parts of the Earth are visible at any given time. If you look closely toward the center right of the Earth, you can see "sunglint," the reflection of sunlight off of the oceans in the direction of the spacecraft.

Notice the color difference between the Earth and the moon. The moon looks dark and reddish. That's the true color of the moon. It looks bright and silvery in our sky, but if we had another bright Earth near the moon in our sky, we'd see how reddish and dark the moon really is.

Also notice the relative size of the Earth and the moon (also correct); it can give you some idea of how small the moon is. The only thing this picture doesn't do is give you an idea of the relative separation of the Earth and moon; the moon is roughly 30 Earth-diameters closer to the spacecraft than the Earth is.

Another version of the video shows the same scene, but it includes some infrared imaging, which brings out vegetation (plants reflect a lot of infrared light). In this version, you can see parts of the continents even better. NASA's Landsat satellites use the same infrared colors to track changes in plant life on Earth, such as these pictures showing the damage caused by illegal logging in Indonesia over a 10 year period.

I find views of the Earth like this are very helpful in reminding myself of our place in the Universe, and how small and unique that place is. Some other views of our planet from outer space:

Special thanks to Phil Plait for posting the EPOXI videos on YouTube and for bringing my attention to them.

Thursday, July 17, 2008

writing about nothing

These days I am working on a fairly boring paper that I intend to publish in one of our professional astronomy journals. The reason it is boring is because it is about nothing. Or, at least, it is about us looking for something and not finding it.

A couple months ago, my colleagues and I announced that we has seen variations in the light of a special type of white dwarf star. This represented the discovery of a new type of variable star, and we continue to work on understanding that star.

That new variable star was discovered as part of a targeted search. We were looking for variations in the light coming from stars such as the one we observed. And we found those variations in one star. But we didn't see them in other stars, and now we need to write a paper describing these non-detections.

There may be many reasons why we didn't see variations in the other stars we targeted:

  1. These other target stars aren't varying.
  2. The other targets are varying, but at a very low level that we can't detect.
  3. We messed up in our data analysis.
And there may be other reasons. Number 3 is fairly straightforward to check; I'm doing that now. I make sure that we were pointed at the right star, and that the other stars around it are acting pretty normal. I make sure that the weather wasn't too bad, and that the clouds weren't too thick. These checks are time consuming, but important. The hard part is choosing between possibilities one and two, and this is crucial for the science! If we claim (and we do) that these other target stars should not be varying, then we have to rule out variations to pretty low levels, better than one percent. And even that may not be good enough; one colleague of mine states that, "if you don't see a star varying, you haven't looked hard enough." And we have other reasons to thinking that variations smaller than the percent level would be something altogether different. But there is a big difference between saying, "it doesn't vary" and "it doesn't vary at a level larger than 1 percent."

A lot of astronomers don't bother publishing non-detections (or "null results," as we often call them). The papers are boring to write, because we usually aren't sure if we should have seen something or not, and it's not as fun as claiming to find something new. But, when it comes to testing theories, a null result can be just as important as finding something. If a theory were to predict that all of our stars should vary in brightness, but only one of a dozen does, than that theory can be ruled out.

Wednesday, July 16, 2008

Telescopes on the moon

Artist's concept of one type of telescope on the moon
Image Credit: NASA

We're going back to the moon. It may be 15 or 20 years until we get there, but NASA is headed that direction. Many people, including a lot of astronomers, are opposed to this new lunar exploration. It will be very expensive, and we aren't sure what the point of the exploration is.

A colleague of mine once argued that we astronomers should be pushing NASA to build a telescope on the moon once we return. His idea, a liquid-mirror telescope, is pictured above. Such a telescope would be quite expensive, and the science it could do may be able to be done more cheaply with orbiting telescopes. But the point was that NASA is much more likely to spend a lot of money on the moon, not on new space telescopes, and if astronomers want a piece of that money, the time to start lobbying is now. Otherwise, we could find ourselves out in the cold once lunar exploration ramps up.

It's sort of like a parent shopping at a high-end luxury store asking their thrifty teenager, "Hey, should we buy you this 2nd-generation iPhone for $500?" The teenager responds, "But we can go to the Apple Store and buy the new iPhone 3G, which is more functional and less then half the price!" To which the parent responds, "You're getting this phone or you're getting nothing." What should the kid do? I think most of us would be tempted to take the phone.

Today, Space.com posted an article on a new design for a lunar telescope that has been proposed. This telescope could be built from materials on the moon. I have no doubt that the cost would be very high and the design technologically challenging to build (as would be the liquid-mirror telescope my colleague proposed). I know very little about the new proposal, such as what wavelengths of light it would be best suited for, or what instruments would go on it, or what scientific question(s) it would address. And, no doubt, NASA would make sure it is a very nice telescope, in terms of these capabilities.

But I wonder if we astronomers need to start thinking much harder about this. Do we want to push for a telescope on the moon? If there is a trade-off between a lunar telescope and a more functional, less-expensive space-based telescope, then let's by all means choose the latter. But I do think it is likely that we might be given the choice of a big lunar telescope, or no big telescope at all. And if we wait 15 years to make up our minds, it will be too late. Who knows what the astronauts will be doing on the moon science-wise, but it certainly won't be astronomy. And we'll have missed out.

There is good astronomy that can be done on the moon. One of the most convincing ideas I've heard is to put a radio telescope on the far side of the moon; the moon will block out radio signals from Earth, allowing us to study signals from space that are currently swamped by our FM radios, our iPhones, our satellite TV, and most every other modern bit of wireless communication. Some types of astronomy, like optical astronomy and, perhaps, infrared astronomy, are better done in orbit so that we don't have to worry about astronaut dust and other activity upsetting the instruments. But both of these fields would not suffer from a lunar telescope.

Astronomers are beginning to assemble our "decadal survey," a 10-year look into the future needs and desires of astronomy. This survey is cited in our funding requests to Congress and NASA. Maybe this time around we should debate the various possibilities of lunar telescopes. If we wait until 2020 to ask, it may be too late.

Tuesday, July 15, 2008

Good luck, Seth and Justyn!

Justyn Maund Seth Redfield
Image Credit:
McDonald Observatory

This summer, two of our fellow postdoctoral researchers here in the Astronomy Department at the University of Texas at Austin are moving on to bigger and better things. Justyn Maund (left), who studies supernovae, or the explosions of stars, has accepted the Tycho Brahe fellowship at the Dark Cosmology Centre in Copenhagen, Denmark. Seth Redfield (right), who studies both extrasolar planets and the gas between the stars, will soon leave to become a professor of astronomy at Wesleyan University in Connecticut.

Both of these positions are big steps forward in Justyn's and Seth's careers. So, while it is quite sad to be losing two good friends, we are all very happy for them and wish them the best in their careers. And, since astronomy is such a small field, we'll be seeing them again and again at conferences, meetings, and other travels. Best of luck to both of you!

Monday, July 14, 2008

Weekend TV

This weekend I was flipping through TV channels, when I stumbled across a show in progress that was discussing the interaction of the mineral magnetite in meteors with Earth's magnetic field and the aurora. I thought that this seemed like a pretty complicated subject to be discussing on TV, but I've seen more complicated things. And I'd missed the start of the show, so I didn't really know what the show was about. Then, in a span of a few seconds, the truth about the show was revealed.

The narrator summed things up roughly as follows: "Dr. X, a plasma physics researcher, has shown that meteors and the Earth's magnetic field may be responsible for the enhanced levels of magnetite." Then the video changed from a pretty movie of the aurora (northern lights) to an animation of a cow floating off the ground up into the air. "But Ms. Y still claims that aliens are abducting the cows."

My brain did a mental flip-flop, and I started laughing really hard. Once I calmed down (and changed the channel), I did some Google "research" and pieced things together. Evidently, cattle are often found dead on the range, and some UFO believers researched a few of these and found what were supposedly enhanced levels of magnetite on the ground in the area. So, I guess the plasma researcher was explaining how you can get magnetite on the ground. I don't need an expert to tell me how to get a dead cow; I can think of many reasons that do not involve aliens.

I hate to be a killjoy and skeptical about this, but I will state unequivocally that aliens are not abducting cattle. Or humans. Or any other creature. Natural explanations for the poor cows' deaths not only exist, but seem much more likely than aliens travelling hundreds of light years for an opportunity to kill cows.

Honestly, I'd like to think that there are intelligent aliens out there. And I'd even welcome a visit, as long as they are more like E.T. than Predator. But a desire to believe aliens exist is no substitute for hard, cold evidence.

What evidence should we require? The only kind that science accepts -- iron-clad. For intelligent life, this could be as dramatic as the appearance of aliens in a public setting or as subtle as detection of communications. But dead cows on the range don't meet that level of proof. Sorry.

Editing Note in the interest of full disclosure: A few hours after posting this article, I realized that my original title had nothing to do with the post (the article went in a totally different direction than I expected), and could be construed as demeaning, even though it wasn't meant to be. So I changed it to the title above before any complaints came in.

Thursday, July 10, 2008

One really strange star cluster

Part of the open star cluster NGC 6791
Image Credit: NASA, ESA, and L. Bedin (STScI)

Sometimes in astronomy we come across a really odd object. And the hard part is knowing whether the object is telling us something fundamental about physics and astronomy, or whether the object is just unique, or some combination of those. Today's example is based on a new Hubble Space Telescope press release (that I was griping a bit about yesterday).

The object in question is an open star cluster in our Milky Way galaxy called NGC 6791. First, some background. Star clusters are groups of stars born at the pretty much same time (a new star cluster is being formed right now in the Orion Nebula) and held together by their own gravity. Star clusters are not individual galaxies, but are parts of our own Milky Way galaxy.

There are two types of star clusters. Globular star clusters (like Messier 13 in the constellation Hercules) are groups of millions of stars. All globulars seemed to have been born in the very early universe, about 12 or 13 billion years ago. Globular star clusters also are very poor in iron and other metals relative to the sun. While almost 2% of the sun is made out of iron, uranium, nickel ,oxygen, carbon, silicon and other elements heavier than hydrogen and helium, only about 0.02% of a globular cluster star is made out of these elements. The reason for this is that stars are factories for the elements, and have been constantly making new elements, so the fraction of those elements goes up over time.

Open star clusters are the other kind of star cluster. They tend to have only a few thousand stars, they tend to be relatively young (most are under 1 billion years old), and they tend to have about the same amount of metal as the sun, give or take a little bit.

But NGC 6791 is, frankly, quite odd. It is old; it's stars seem to be about 8 billion years old (more on that later). This is much younger than the globular clusters, but older than any other open star cluster. Since it is so old, you might expect that its stars have a metal content between that of the globular clusters and the sun, but in fact it has over twice as much metal as the sun! And NGC 6791 has many more stars than any other open cluster, despite the fact that open clusters tend to lose stars over time. Lastly, NGC 6791 has a lot of really strange types of stars in it. So, it has always been viewed as odd, and its true nature has always been a source of controversy.

A group of scientists led by Italian astronomer Luigi Bedin looked at NGC 6791 with the Hubble Space Telescope in order to study its white dwarfs. White dwarfs are the ashes of dead stars; over time, a white dwarf cools and slowly fades away (just like what happens when you turn off the heat on an element on an electric stove, or when a blacksmith pulls red-hot metal out of a fire). We can estimate how old a white dwarf is by looking at how cool it is and using models to tell us when the star that made the white dwarf died (this is some of my own research).

When Bedin and his collaborators did this for NGC 6791, they found something odd. First, there were two groups of white dwarfs, one that seemed to be 4 billion years old, and another that seemed to be 6 billion years old. But, as I said above, the still-living stars in the star cluster look to be 8 billion years old. What's going on? We don't really know. But we do have some ideas.

First, we use models to get ages of stars and ages of white dwarfs. Those models are not perfect, and there are some uncertainties about them. In stars, a process called convection (which is like boiling or the turbulence that creates thunderstorms) mixes the stars, and that mixing can bring some new fuel to the star's nuclear furnace. We don't really know exactly how much of this mixing happens, so we guess. And that while these are highly educated guesses, they might be wrong. So, the 8 billion year age for the cluster may be wrong by as much as a billion years.

Also, the white dwarf ages have some uncertainties, especially for old white dwarfs. Old white dwarfs, as they cool, start to crystallize, forming giant, ultra-dense diamonds in space. That process of crystallization is not fully understood. Also, old white dwarfs may undergo a process called fractionation, where the heavier metals sink toward the center of the white dwarf. That sinking process can slow down the white dwarf's cooling rate, making an old white dwarf appear younger than it really is. This process (which may not even happen; it is very controversial) would be more likely to happen in white dwarfs with more metal. And, remember, this star cluster has more metal than any other star cluster!

So, I don't think that the 6-billion year age of one set of white dwarfs necessarily disagrees with the 8-billion year age from the stars. It would be kinda like looking at two separate people, saying, "Mr. X looks to be between 50 an 60 years old, and Mr. Y looks to be between 60 and 70, so I'll guess that Mr. X is 55 and Mr. Y is 65." Then you find out that they are both 60 years old. I think the same thing is happening here.

The bigger question is with the second group of white dwarfs, those that look only 4 billion years old. Here there are two ideas. Bedin and collaborators have suggested that these white dwarfs may be binary stars. Binary stars look like a single star from the Earth, but are really two stars orbiting each other closely enough that we can't tell them apart. The main effect of binary white dwarfs would be to produce a single point that looks brighter than a lone white dwarf would be. Since we get white dwarf ages from how bright they look (because they fade over time), we would mis-interpret binary white dwarfs as younger white dwarfs. In most open star clusters, about half of the stars are in binaries, and if that holds true in NGC 6791, then maybe the "young" white dwarfs are really just old twins.

But there is another option. An acquaintance of mine, Jason Kalirai at the University of California Santa Cruz, looked in detail at the brightest white dwarfs in this star cluster. He found that these white dwarfs were kinda wimpy, only about 2/3 as massive as they should be. (Most white dwarfs are about 60% the mass of the sun; these were about 40% the mass of the sun). White dwarfs with masses this low cool differently than normal white dwarfs (for reasons I don't want to go into). If you analyze the apparently younger white dwarfs as if they were merely featherweight white dwarfs, you would find that their ages are about 6 or 7 billion years, the same as the other white dwarfs.

But these featherweight white dwarfs can only exist if their parent stars ended their lives differently from the way we think most stars do. Some people (such as another acquaintance, astronomer Brad Hansen at UCLA) have suggested that the high amount of metals in the stars could cause the stars to lose a lot more matter at the end of their lives. There are other ideas that might work, though.

In short, this star cluster is a really odd one. It is very old, but it has more metal than any other star cluster (and we would think that newer star clusters should have more metals). The cluster has more stars than any other open star cluster, although it has been losing stars over its entire, long lifetime. The cluster has some really weird stars (which I haven't talked about here). The ages of the dead stars in the cluster may be different from the ages of the living stars. And even the dead stars disagree on how old they are, or they maybe they formed in multiple and unexpected ways. The jury is still out! Is this cluster just weird, or is it telling us that we don't really understand the life cycles of stars as well as we thought we did?The only thing for certain is that this cluster will continue to be studied for years to come.

Wednesday, July 09, 2008

The strange world of embargoed science

Press releases on scientific discoveries are sometimes "embargoed," meaning that the press is given materials in advance, but only on the condition that the findings not be released before a given date (often the date of a press conference or publication of a magazine). Nature, one of the most prestigious scientific journals, is extraordinarily strict; at one point, they requested that scientists not publish their work as "pre-prints" (copies of articles distributed in advance of official publication, primarily to other scientists in the same field). That borders on being scientifically unethical, as science thrives only on the free flow of information. Thankfully Nature backed down on that request.

Anyway, I'm on a NASA email list with advanced notice of press releases. I'm not sure how I got on the list, but I get notices anyway (I may have requested membership somewhere at some point, but I don't remember). Typically the news is embargoed for a day or two.

Yesterday, I got an announcement about a press release that will be made tomorrow, and strict notice of the media embargo was given. Looking at the release, I had to laugh at how silly the embargo is. The topic is science close to what I work on, and the results have been freely available on our preprint server for six months! The results are also quite intriguing, so I've been chatting about it with colleagues, and I even spoke about it with the science teachers at the workshop I helped lead a couple of weeks ago. So the idea of an embargo is, frankly, silly.

Now, I won't spoil the fun and talk about NASA's release early (there are some cool pictures); I'll talk about it tomorrow. But I'd urge media outlets to re-think the purpose of an embargo. If you are going to make a press release, is there a good reason for embargoing the news? If you just want everyone to get the data at the same time, why not release everything at the time of the press conference (if there is one)?

Monday, July 07, 2008

Back home again




Strange Brew comic featuring astronomers
Image Credit: John Deering / Creators Syndicate, Inc. / Hosted by gocomics.com
Three weeks is a long time to be away from one's desk. Over that time, I've visited family in California and Illinois, helped facilitate a high school science teacher's continuing education workshop at McDonald Observatory in west Texas, and observed with the Keck Telescope on the Big Island of Hawaii. No wonder I slept most of the weekend away, as my body has no clue what time zone it is in. I think I'm somewhere in central Asia right now.
So, as you might expect, I have a mountain of email and regular mail and reading and phone messages to catch up on. It's always a bit of a rude awakening to come back to emails from people wondering why I've been ignoring them for three weeks, despite my having told them that I'm gone. I also need to catch up on astronomy news, as I don't know what (if anything) has happened in the past few weeks.
Some of my colleagues will also be coming home today from a major conference in Spain that I wanted to go to, but I wanted to go observing even more. So, I'll have to pick their brains and see what they learned. And, should any of it be exciting, I'll be sure to let you know!