Professor Astronomy's Astronomy Blog

Planets come and planets go, but not in 2012

2009-11-13T17:18:00.000-06:00

Image Credit: NASA / Don Davis

Today, the movie 2012 opens in theaters. The basic plot is that the Mayan calendar ends on the solstice in 2012, portending doom for all on this planet. I'm not going to see the movie, as I'm not a fan of disaster movies (except, perhaps, the Samuel L. Bronkowitz classic "That's Armageddon"). If you want to see major cities around the world destroyed and humanity struggle to survive, then this is probably the film for you.

I mention the film because there is an ever-growing chorus of people who think that the world actually will end on December 21, 2012. These people are wrong, their claims are made on bad (and often fabricated) science, and many of them are just out to make money off of gullible people. Rather than go through a litany of the claims about 2012, let me point you to a few reputable websites that have the science and the cultural history correct:

2012: Beginning of the End or Why the World Won't End? -- NASA's FAQ on the 2012 myths
The Great 2012 Doomsday Scare -- an article from Sky & Telescope magazine reprinted on NASA's website
2012 FAQ -- from the Foundation for the Advancement of Mesoamerican Studies, Inc. If anyone can interpret the Mayan calendar, I'll believe the people who actually study the Mayan civilization

I mention this whole 2012 business because of anecdotes I've been reading. Young people have been asking if it is best to commit suicide than to try and survive 2012. Some people are spending loads of money to buy prefabricated shelters that supposedly will protect them. This is not simply about yet another doomsday prediction based on invented "science"; we are talking about hucksters willing to ruin the lives and livelihoods of innocent people to make a quick buck; we are talking about everyday people who are scared because they heard misinformation about a cataclysm that is not going to happen. (In case anyone has forgotten, dates for end of the world have been coming and going for nearly 5000 years. Check out the list.)

I've seen comments on other blogs by people who think NASA is wasting money by trying to debunk the 2012 doomsday predictions. First, the website doesn't cost that much money -- the web server already existed, and the salary cost for the appropriate research and page design is probably less than the cost of one bolt on the next shuttle launch's external tank. If NASA's efforts can help people to realize that folks who claim 2012 will be the end of the world are full of it, then the investment is more than worthwhile.

If you know anyone who is worried about some looming disaster in 2012, please point them to reliable resources and try and dispel them of that mistaken notion. Again, we are talking about our friends and neighbors who are being bilked and scared by a nonexistent threat.

To those who will claim that I'm just part of a big conspiracy to hide the truth, you're sadly misinformed. If I suspected that the world was going to end or an asteroid was going to hit or the Earth's rotation were going to stop or Mayan gods were going to descend and wreak havoc on the world, I would not be sitting in a dark little office in front of a computer screen writing this blog. I'd be out enjoying life, exploring nature, and running up a huge tab because I'd know I'd never have to pay. Even if "they" were to threaten to kill me, I still wouldn't be here. If I'm going to die in the great catastrophe of 2012, then "they" would not be able to threaten me.

Water, water, everywhere.

2009-11-13T14:51:00.000-06:00

Last month, after NASA's LCROSS spacecraft failed to make a noticeable splash when landing on the moon, I blogged about how it could take months for the data to be analyzed. Well, it took only about five weeks. Today, NASA announced that LCROSS did indeed detect water, and a fair amount of it. Final results will still take months, but the data are clear that water was present.

Why didn't we see the show from Earth? Part of the reason is that the probe crashed behind the big mountain visible in the bottom of this picture, so the mountain likely blocked our view of some or most of the plume. It's also just difficult to predict what will happen when you crash one object into another.

Anyway, the LCROSS work is still just beginning, so be on the lookout for more results in future months!

Congratulations Steve!

2009-11-06T15:36:00.000-06:00

Image Credit: Steven DeGennaro

Today, we astronomers are honored to welcome yet another newly-minted PhD into our midst: Steven DeGennaro. Steve is a graduate student here at the University of Texas at Austin, and this afternoon he successfully defended his doctoral dissertation.

Steve is in the white dwarf group here at Texas, so I've gotten to work closely with him over the last three years. He has studied many aspects of white dwarf astronomy, and loves to get down and dirty in the awful details of analysis, including selection functions (What type of stars were various observations sensitive to? It's easy to answer in a general way, and very difficult to determine in detail) and statistical analysis.

Steve's dissertation covers many topics, with one central focus being how to better determine the ages of clusters of stars and their white dwarfs. Steve, with collaborators here at Texas, developed a computer program that uses Bayesian statistics. Bayesian statistics are often viewed with skepticism in astronomy. In Bayesian analysis, it is possible to take a lot of data that has many interelated parameters and observations and producing a self-consistent description of the data. It's conceptually simple but fiendishly difficult to execute properly. Steve has produced a program that has been shown to work (i.e., produce the answers we expect) on some of the best-studied star clusters in the sky, such as the Hyades.

Steve was the observer at the telescope when we discovered our new class of pulsating white dwarfs, the carbon atmosphere white dwarfs. For this reason, we sometimes refer to those stars among ourselves as DeGennaro's Degenerates (which would also be a good name for a rock band).

Steve has also helped out at the last three white dwarf teacher workshops. He bonds well with the teachers (partly because he previously served a tour of duty as a high school science teacher), and he did an excellent job training our participants how to use the telescopes and cameras.

Now his dissertation is complete, Steve will be leaving the field of astronomy to work in motion pictures. Right now, he's excelling as a sound editor in local productions. While there are many astronomers who view this as a waste or as selling out, I disagree. Steve's done excellent astronomy research, and the field will miss his contributions. But there is also no reason to keep plugging away at climbing the academic ladder if one's preferences lie elsewhere.

Too often, I think astronomers tend to undervalue the accomplishments of reaching various milestones that the rest of society admires, such as earning a master's degree and a doctorate degree. For many astronomers, those achievements just mean you've jumped through another hoop and now have to face the daunting climb up the next step. But these are impressive accomplishments, and anyone who wants to admire their accomplishment and then head off in another direction should be given a rousing sendoff and be remembered fondly for their accomplishments, not with sadness over the academic career that might have been.

So, in a few years, when you notice that the sound quality of motion pictures has increased a hundredfold due to a new DeGennaro editing process, just remember that astronomy is what made it possible.

Good luck, Steve!

Begging for money

2009-11-05T10:46:00.000-06:00

The past several weeks I've been working on funding proposals for the National Science Foundation. This just means I'm asking the government for money to do research. And, despite what you may think, the government is stingy. There are a lot of astronomers, and limited resources for research. We have to spell out our proposed research in only 15 pages, and in that small amount of space we have to make people excited about our research and convince them that it is important and will succeed. We have to anticipate and answer questions the reviewers will have about our science and proposed methods.

We also have to justify every penny we plan to spend. It's not easy. How do you accurately estimate the costs of attending a conference that you know will happen somewhere in the world in either 2012 or 2013? How many trips to which telescopes will we have to take? Will we need new computers along the line? What will our salary needs be over the next three or four years? This is hard, too. My salary needs will be a lot less if I am offered a job as a professor somewhere, as that will pay my salary for at least 9 months of the year. But will I get that job this year? Or next year? Or the year after that? How many papers announcing our results will we need to write? How many pages will each of these papers be? How much money will I need for phone bills and photocopying in 2012?

We also have to discuss how our research will make an impact in the world outside of astronomy research. This includes what sort of education and public outreach we will do if we get the money (such as this blogging or the teacher workshops I've helped with in the past). The National Science Foundation takes this section of proposals very seriously. If we want money, we cannot merely hide in our offices, write inscrutable scientific papers, and spend taxpayer money. We have to show that we are sharing what we learn with the world outside of academia.

Anyway, that's a big reason I've been kinda quiet recently. In 10 days, this will all be a bad dream, and I can get back to writing job applications. And 2 or 3 months from now, that will be finished, and I can get around to writing proposals to use telescopes. After that is done, I can get back to doing science. Or it may be time to start applying for more funding. We shall see.

A bitter retirement

2009-11-04T11:59:00.000-06:00

Image Credit: James Liebert

Those of you who regularly read my blog know that I often write about colleagues who are moving on to the next step in their careers, be it postdoctoral researchers who get jobs as professors, or graduate students who finish their PhDs (one of those is coming up later this week, we hope!). Each of those are big steps, and worthy of celebration. Retirements are another big step in astronomy careers, and should also be cause for singing and dancing in the streets.

One of my mentors and good friends is retiring from astronomy this week after a long and very successful career in astronomy. I wish I could say that I am very happy, but I am not. This is not the whistful sadness of wishing a friend a fond farewell (for most astronomers, retirement is rarely accompanied by a sudden change -- retired astronomers routinely keep doing research, showing up at the office, and even mentoring PhD students.) This is the sadness of watching a friend self-destruct, and not being able to help him.

My friend and mentor is Professor James Liebert (pictured above in celebration after the Kansas Jayhawks won the NCAA basketball championship in 2008). Dr. Liebert is one of the world's foremost experts on white dwarf stars, though he has also done research on brown dwarfs and, in decades past, even distant galaxies. However, as one colleague described him, Liebert's brain has essentially two parts. Half is dedicated to white dwarfs, and the other half to Kansas Jayhawk basketball.

During his career, Liebert has used white dwarfs to determine the age of parts of our Milky Way galaxy. He's studied how massive white dwarfs are, and how fast our galaxy is producing white dwarfs. He's worked on the composition of white dwarfs. He's researched interacting white dwarf stars and magnetic white dwarf stars. You can show Liebert a spectrum of a white dwarf, and he can, just by eyeballing it, tell you fairly accurately how hot and how massive that white dwarf is. At meetings of white dwarf scientists, Liebert is probably the best-known person in the room.

Liebert also cares very much for his students and his collaborators. He knows the family histories of many of his students, has been invited to weddings, and inquires about the well-being of family members he may never have met, perhaps years after he learns of an illness or struggle with which that relative is struggling. He agonizes over the careers of those younger people he's worked with, even to the point of offering to resign or draw less salary if such a person is hired.

Liebert began his studies in astronomy during the Vietnam War, and took a break from his studies to serve a stint in the Navy. He can't say exactly what he did, but I surmise he was involved in intelligence gathering. Liebert attended Berkeley toward the end of the student unrest of the 1960s and early 1970s. He worked on his PhD with Hy Spinrad, who is well-known for work on distant galaxies. But Liebert was intrigued by the white dwarf stars, and he used the 3-meter telescope at Lick Observatory to take spectra of many white dwarf stars, all while helping Spinrad study radio galaxies and other distant faint fuzzy objects.

I met Liebert when I moved to the University of Arizona Department of Astronomy in 2002. My PhD work had been on white dwarf stars, but my primary work at Arizona involved studying distant galaxies. Still, Liebert took pity on my and gave me a lot of tutoring in white dwarf science. There are several subtleties involved in studying white dwarf stars that affect their usefulness as astrophysical probes. I absorbed as much of this information from Liebert as I could, and that knowledge has helped me to grow and mature as a scientist. Since leaving Arizona three years ago, I've kept in touch with Liebert, visiting Arizona on many occasions and working on joint research problems.

Over the past year, though, Liebert has succumbed to substance abuse. Perhaps he's been battling this for a long time and has became more susceptible as he's aged, or perhaps it began with self-medication for other medical issues. But the scientifically productive and caring man Liebert usually was has transformed into a combative, selfish person that we, his friends and colleagues, do not recognize. Despite multiple trips to the hospital and treatment centers, Liebert is not yet on the road to recovery. Early retirement was offered to Liebert to allow him the freedom to seek whatever recovery he deems best, without having to worry about teaching classes or ignoring students. If and when he is clean and sober, he can then take up the life of the typical retired professor. We all hope he is willing and able to take advantage of this opportunity.

I tell this story not to denigrate Liebert; substance abuse is a disease that affects people from all walks of life and is not limited to the poor or the unintelligent or the selfish. I tell the story for a few reasons. First, I want to acknowledge the remarkable career of Professor Liebert and his contributions to both the science of astronomy and to my own personal career, and I want to with him well on what is a treacherous road to recovery.

Second, I wish to share a few lessons that I have learned. I, along with many people around Liebert, made the very common mistake of not recognizing or admitting his substance abuse problem in the early going. I made excuses for him, I looked for other medical issues that may have been responsible for the same symptoms, and I did not confront Liebert on these problems soon enough. I don't know that an earlier admission on my part would have changed anything, since the choice to admit the problem and begin recovery is Liebert's and his alone, a choice he still hasn't made. I regret my slowness and trepidation.

Liebert's problems have also strained relations between many good people at the University of Arizona. We all have had our own opinions as to Liebert's problems, the degree of his problems, and what the best course of action is. As Liebert has sunken further into his disease, these differing opinions have sharpened to the point where some friends and colleagues are near the breaking point. What makes this exceptionally sad is that we all want the same end -- we want our sharp scientist and caring friend back and healthy. We disagree on how to get there. And, since Liebert has no immediate family (he does have cousins and an aunt and uncle who are working hard on his behalf), we individually feel like we need to take Liebert's recovery on our own shoulders and do what we each feel is best. This is complicated by the fact that, since many of Liebert's closest friends are in the workplace, University rules and regulations constrain what can be done. It is horrifying but true that we can be limited in helping each other by the same privacy rules that were written to protect us.

So, I hope and pray that Liebert's retirement will encourage him on the long, hard, and endless journey of recovery. I honor the man I once knew and his profound contributions to the science of astronomy. And I still cling to the perhaps overly-optimistic hope that, one day in the not-to-distant future, I can again collaborate with Liebert on studying the secrets of the stars.

A prized lecture

2009-10-28T17:56:00.000-05:00

Image Credit: McDonald Observatory

Today we were treated to a lecture in memory of Antoinette de Vaucouleurs, who was an astronomer here at the University of Texas at Austin for 25 years. She is well-known for extensive work on the photometry and radial velocities of galaxies, often collaborating with her husband, astronomer Gerard de Vaucouleurs. She continued working until just ten weeks before her death of bone marrow cancer in 1987. You can read more about her life and work here.

Every year, the Department of Astronomy invites an outstanding astronomer to receive a memorial medal, and to give public and research lectures in recognition of their lifetime of achievements. Past recipients read like a who's who of BIG astronomers, including Margaret Burbidge, Vera Rubin, Don Osterbrock, Sandy Faber, Frank Shu, and Nobel Laureate John Mather, among many other equally-distinguished astronomers.

This year, we had the honor of hosting Dr. Rashid Sunyaev, director of the Max Planck Institute for Astrophysics in Garching, Germany, and Chief Scientist of the Russian Academy of Sciences Space Research Institute in Moscow. Dr. Sunyaev is well-known for making many important predictions about the cosmic microwave background and X-ray radiation from black holes, many of which have been found to be true. One of the things that I particularly like about much of his work is how he focuses on the observable signatures of the physical objects he is interested in. It's one thing to hypothesize about some of the earliest structures in the Universe; it's another thing altogether to also tell us observers how we might be able to see these structures.

During today's research lecture, Dr. Sunyaev gave an overview of his most famous work on clusters of galaxies and cosmology, sprinkled with personal anecdotes about his advisor Dr. Yakov Zeldovich. He also gave some advice to the graduate students, such as to publish results about "beautiful physics", even if the observations needed to test the prediction seem technically impossible, because we don't know how far technology may go in the next decades. He also quipped that theorists have to be smart, but it's okay for them to be wrong, while observers don't have to be smart, but they'd better always be right. Sunyaev was also very excited about some new results that will be coming out of the Planck satellite and telescopes at the South Pole, but he couldn't tell us details about the results yet because the findings are still being verified.

It is always a real morale booster to see talks by people who are so clearly passionate about their research and optimistic about the potential for new, exciting discoveries in the future.

Clear Skies Abundant

2009-10-24T06:59:00.000-05:00

Image Credit: McDonald Observatory

Crystal clear skies. Maybe even clearer. This is how I like my observing runs.

I'm finishing the 10th night of a 13-night observing run dedicated to looking at my favorite white dwarf stars. I haven't been out here all ten nights, as two of my colleagues kindly volunteered to cover the first nine nights of the run. In those nine nights, the weather was ideal for seven nights. Tonight has also been great, and it looks like at least two and maybe all three of the remaining nights will also be clear. Given that two-thirds of my telescope time has been clouded out over the past 18 months, I'm grateful to finally be getting a lot of high-quality data.

This run has had me worried for a long time, and not because of triskaidekaphobia. Two days before the run started, one of my volunteers had a family emergency, so I had a stressful 48 hours rearranging the observing schedule. Then one of my cats got quite ill, and I wasn't sure how to make sure she was taken care of while I was gone. (Thankfully she recovered enough that my pet sitter has been able to take care of her.) Then one of my volunteer observers fell ill here at the mountain (she fully recovered). About the same time, I got word from Arizona that one of my colleagues there was in the hospital and not doing very well (he's not recovered, but at least is stable and was able to go home). Lastly, as I was preparing to leave Austin, I accidentally dinged the side of another car with my car door; the owner of that car got absolutely livid over the 1/8-inch long scratch (no dent, but I did flake the paint and primer off), so I spent an hour on the phone with insurance.

Still, the clear skies and good data are worth most of the stress. The moon and Jupiter dominated the evening skies, and all morning I've seen a dribbling of bright, fast-moving meteors, the last dregs of this week's Orionid meteor shower. Now the planets Venus and Saturn are rising, and the first hints of dawn are on the eastern horizon. Time for bed!

Galilean Nights this weekend

2009-10-21T10:28:00.000-05:00

Image Credit: IYA2009 / James White

Galilean Nights, one of the cornerstone projects of the 2009 International Year of Astronomy, takes place around the world this weekend! The goal of the weekend is to encourage those around us to look through a telescope at the same celestial objects that Galileo looked at 400 years ago, leading to a revolution in our understanding of the Universe and giving a new birth to the science of astronomy. This weekend, the moon and Jupiter are both well-placed to see in the early evening sky. And, if you are a morning person, Venus and Saturn are both low in the pre-dawn sky, rising about 1 to 1 1/2 hours before the sun. The Orionid meteors, bits of dust shed by Halley's Comet long ago, will also be an occasional visitor in the evening and morning skies.

Do you want to participate? You don't need any experience. Many planetariums and observatories will be having festivities; contact them to find the place and time. You can also find a nearby event from the Galilean Nights website: http://www.galileannights.org/find_event.html. If you own a telescope, why not pull it out on a local sidewalk and show off the moon and Jupiter this weekend to friends, family and neighbors?

If you don't have a telescope and can't find a nearby event, you can also go out and look with your eye. The moon will be obvious, and the planet Jupiter is the brightest object in the evening southern sky (if you live north of the equator). 400 years ago, Galileo alone knew that Jupiter had its own moons performing an intricate dance around it; now you, from the comfort of your own living room, can use a computer to see pictures of those moons taken by robots, pictures that give some hope that some other form of life may be swimming in oceans under dozens of miles of ice. And think about how we now can find worlds like Jupiter around stars hundreds of light years away, and how very soon we will know about Earth-like planets around those same distant stars.

Sorry!

2009-10-21T10:00:00.000-05:00

Sorry to a handful of commenters whose comments were awaiting moderation and just got rejected. I was trying to reject an advertisement and accidentally clicked on the "Reject All" button. My goof.

Just as a brief reminder on comment policy, any comments on posts over 7 days old have to be moderated to keep spammers away. It can take me a few days to get around to it, depending on my schedule. Thanks for your patience. I accept most comments, but will reject anything that is obviously spam, that is way off topic, that is not family-friendly, or that is just a flame war.

Stop the world and let me off!

2009-10-20T08:48:00.000-05:00

The past two weeks have been horribly busy with all kinds of things I hope to blog about over the weekend. Yesterday and today I'm attending a postdoc-led symposium here at Texas. (Here is my blog post from the last edition of this symposium two years ago). Alas, it's keeping me even busier, but I'll summarize all the cool things I've learned in a few days.

I, for one, welcome our new grasshopper overlords

2009-10-16T11:18:00.000-05:00

Image Credit: McDonald Observatory / MONET / D. Doss
What was that last night in the skies above McDonald Observatory? An odd cloud? An alien spacecraft arriving from the Orion Nebula? Or (shudder) Melanoplus lakinus? We may never know. By the time crack government agents arrived, it was gone.

Did NASA's Moon impact Fail?

2009-10-09T21:58:00.001-05:00

Image Credit: Palomar Observatory / Caltech

No. At least, not yet, and I don't think it will.

For a few months now, NASA has been hyping this morning's impact of the LCROSS spacecraft with a shadowed crater on the Moon. Many websites (including this blog yesterday) passed on information on how people with 10-inch or larger telescopes could watch the event, yet professional observatories with 200-inch diameter telescopes didn't see anything obvious. Because of this, many websites, bloggers, and news casts have painted the LCROSS mission as a fizzle and a failure. This is as unfair and exaggerated as the predictions of spectacular fireworks were.

I do believe now that NASA overhyped the LCROSS impact, at least in terms of what we might be able to see from the Earth. But I do not believe the mission has failed. And that's because science is not about getting the answer we want, it's about getting the answer right.

The LCROSS spacecraft's main mission was to look for water on the Moon, specifically water frozen as ice in the permanently-shadowed craters at the Moon's poles. The methodology that the scientists who lead the mission chose was to impact a spent rocket engine into a crater, and then fly a spacecraft through the plume of debris tossed into space. The LCROSS spacecraft would analyze the content and structure of the plume before crashing into the Moon itself, sending up a second plume of debris. With luck, these plumes would also have risen high enough for Earth-based telescopes to see; these telescopes could then provide even more data.

All of this worked except some of the last part. The spent rocket engine collided with the Moon, LCROSS flew through the debris plume, made measurements, and sent those to Earth before colliding with the Moon itself. LCROSS saw a flash from the first crash and did indeed detect debris. Some satellites, including LCROSS's sister spacecraft, the Lunar Reconnaissance Orbiter (LRO), did detect the debris plume. But, at first glance, many telescopes did not. Palomar did not, Hubble did not.

What does this mean? It means the debris plume (which we know was created, because both LCROSS and LRO saw it) was not as big or substantial as mission scientists thought they might see. This means the Moon is different than we thought, at least in these polar craters. This means we're learning something unexpected. That's science! In fact, it's more interesting than if we'd seen a big plume of water like we hoped, because it means we scientists were wrong and that there's something we still need to learn. That's not failure, it's success.

Now, it still may be possible to snatch failure from the jaws of victory. Maybe we'll learn that some human error was responsible for the lack of plumes. Maybe some computer made a mistake on the size of the debris plume. Maybe the trajectory of the impactors was miscalculated. Maybe the wrong model of lunar ice and soil was used. Maybe the Hubble was pointing just the tiniest fraction of a degree in the wrong direction. As the scientists involved in the LCROSS team analyze their data, they'll be checking all of these things, even as they look for signatures of water and the other components of the debris plumes. But my gut feeling is that everything went right.

So, what happened? Where was the towering pillar of water rising from craters that haven't seen the sun in two billion years? I'm just guessing, but I suspect that big plume we were all expecting to see was one of the best-case scenarios. NASA probably felt comfortable predicting the best-case scenario after the spectacular fireworks of the Deep Impact mission, which used the same basic idea to probe the comet Temple 1. Certainly the claims of fireworks got the mission a lot of attention, but when the best-case scenario failed to materialize, it led to a lot of disappointment. I wonder what would have happened if NASA said, "You probably won't see anything, but there's a small chance you'll see fireworks on the moon." Perhaps fewer people would have been watching, but at least NASA wouldn't be the butt of jokes this evening.

Whatever problems they've been handed in public outreach, the LCROSS team has put together an ambitious mission that has, so far, worked. Time will tell how much we'll learn from the mission. How much time? Having worked with tons of data myself, we're talking months. The team will look at the data, study it, poke it, prod it, and push the data to its limits. Once they are sure of what they've found, they'll tell us. So, we just need to wait. I hate waiting.

Two impacts that will happen, one that won't

2009-10-08T11:30:00.002-05:00

Image Credit: NASA

Early tomorrow morning, the moon will be hit by two fast-moving bits of space debris. In 2036, the Earth will almost certainly not be hit by a 250 yard-wide rock. All three of these pieces of news make me happy.

First, the moon. The two bits of "space debris" are NASA's LCROSS probe and its spent Centaur booster rocket. The rocket, weighing in at about 2.5 tons, will hit first, impacting the crater Cabeus (near the moon's south pole) at 7:31 am (and 19 seconds) EDT tomorrow, while moving at a speed of 9000 kilometers per hour. This hit should gouge a crater about 20 meters wide and 5 meters deep, and may toss as much as 385 tons of lunar soil and rock into the air.

NASA wants this plume of debris to be tossed up, because the LCROSS spacecraft is going to fly through the plume, taking pictures, analyzing the chemical makeup of the debris, and sending that information back to Earth before it collides with the moon itself 4 and a half minutes later. That impact will create a second plume of debris. Earth-based telescopes on the night-side of the Earth will be staring at and analyzing the impact site, too, assuming the weather is good. (The weather at the observatories in Hawaii is looking chancy).

The whole point of these two collisions is to look for one specific chemical: water. Satellites have found indirect evidence of water on the moon, including a recent claim of a few-molecule-thin layer over large parts of the moon. The idea here is that the floor of the crater Cabeus never sees the sun, so if any water is brought into the moon by comets, it may freeze out and stay in these craters.

Finding water on the moon has two important implications. First, there is the functional implication that if there is water on the moon, any lunar bases we humans build might be able to use it instead of bringing water from Earth. Water is heavy, and every pound of material we send to the moon costs thousands of dollars. Given that a pound of water is only about a half liter (a pint's a pound the world around), a bottle of Earth water would cost ten thousand dollars. Granted, it could (and would) be recycled, but if you thought Perrier was expensive... (Do you think a moon base vending machine would take ten-thousand-dollar bills? Do you think any astronauts would recognize Salmon Chase?)

The scientific side of lunar water is also quite interesting. Many models of the early solar system claim that water should not have been able to exist where the Earth formed, yet we are positively swimming in the stuff. Other models say that we may have originally had water, but big collisions with protoplanets when the Earth formed should have dried the Earth out. Yet they didn't. Or perhaps the very early Earth was dry, and comets brought water to the Earth. By studying the detailed composition of any moon water, planetary scientists can hopefully determine where that water came from (comets? Original to the moon?).

If you are interested in watching the LCROSS impact, your best bet is to tune in to NASA TV starting at 6:15am EDT (3:15am Pacific) to watch the live broadcast. NASA TV will show pictures from the LCROSS satellite as they come in, plus any pictures and video from telescopes observing the impact. If you live west of the Mississippi River, you may have a chance of seeing the impact in the pre-dawn sky, but you'll need a telescope of at least 10-inches in diameter. Universe Today has detailed instructions for anyone wanting to see it themselves.

So much for the impacts that will happen. Now, onto the one that won't. In late 2004, a major stir was caused by the announcement that the 250-meter wide asteroid Apophis had a 2% chance of hitting the Earth in 2029. As astronomers gathered more data on this asteroid, we were able to better calculate its orbit and determine that it will not hit the Earth in 2029, though it will pass very close, only about 20,000 miles away. This is inside the orbit of geosynchronous satellites! There also was a chance (1-in-45,000) that, if Apophis passed through a tiny kidney-shaped region of space during its 2029 passage of Earth, it would be put on an orbit that would collide with the Earth in 2036.

Yesterday, new calculations based on combining new data with the older observations of the asteroid gave a much more accurate prediction of the asteroid's path. The result lowered the chance of a collision in 2036 to a very tiny chance: 1-in-4 million. Now, that chance is still not zero, but it is so incredibly small we can breathe easy. Now, we astronomers will keep looking and recalculating its orbit. Because this asteroid comes so close to Earth, we're going to get some excellent data on it in the next twenty years. These data will tell us a lot about the asteroid, where it came from, what it is made out of, what its structure is. These data will also allow us to determine its orbit even more precisely, and to plan out a strategy should we find that the asteroid will hit Earth in the even more distant future.

If you want to know more about near-Earth asteroids and the likelihood of the Earth being hit any time soon, check out the Asteroid Watch website for the most current news and science.

One last note. Some news reports have said that NASA is "bombing" the Moon with LCROSS. That's wrong. I don't know who used the phrase first (I actually think I heard it from NASA), but it's misleading. There are no explosives on the satellite or the Centaur booster. Explosives wouldn't do much, and would add additional chemicals to the analysis that would be hard to take out. We're just crashing the probes into the Moon. Also, some people think we are damaging/trashing the Moon with this impact. Meteors this size routinely hit the Moon (I don't know the exact frequency, but couple-ton fireballs burn up in the Earth's atmosphere several times a year, such as over Canada a few weeks ago). We're just adding one event to a common occurrence.

2009 Nobel Prize for Physics Part 2: Fiber Optics

2009-10-07T11:22:00.000-05:00

Image Credit: HETDEX / McDonald Observatory

As I mentioned yesterday, this year's Nobel Prize in Physics was shared between scientists who developed digital imaging circuits known as Charge-Coupled Devices (CCDs) and a scientist, Dr. Charles Kao, who designed the first fiber optic cables that were useful for long-distance data communication. Yesterday I blogged about the astronomy uses of CCDs, so today I'll talk about the astronomy uses of fiber optic cables.

At most telescopes, there are two primary kinds of instruments. One kind is the imaging camera, which simply takes pictures of the sky. That's easy enough to understand, and fairly straightforward to build. (Don't get me wrong, building any astronomical instrument for a big telescope is very hard.) The other type of instrument is a spectrograph, which splits light into its component colors. These spectra are most often used for determining the chemical composition of things and for measuring how fast things are moving.

One problem with spectrographs in the past has that the number of stars or galaxies you can look at at one time is limited. Some spectrographs only allow you to look at one star (which is fine if there's only one star in some area of the sky that you are interested in), Some allow you to look at multiple stars or galaxies, but which ones you can look at are constrained by geometry -- you can't analyze spectra of individual objects if they criss-cross or lie on top of each other. And if you are looking at a two-dimensional object, like a galaxy or nebula, traditional spectral only allow you to get a spectrum of a long thin slice of the object. So, how can we get around these problems?

One solution to this problem has been fiber optics. With a fiber optic spectrograph, astronomers place fiber optic cables over each of the stars or galaxies they are interested in. These fibers are then rearranged in the camera so that the resulting spectra do not overlap. It's very clever, and it's allowed astronomers to take spectra of hundreds of objects at once (Sean at Cosmic Variance blogged yesterday about how this capability allowed the Sloan Digital Sky Survey to survey a large chunk of the nearby Universe). Or, if the astronomer wants to take a spectrum of an entire galaxy, she can just squeeze all on the fibers into a big bundle, so that light from any part of the galaxy will land on one of the fibers, giving us a spectrum of everything. The only trick is remembering which spectrum belongs to which fiber and where that fiber was on the sky, so we have to use careful documentation and computer controls to keep track of those things.

The McDonald Observatory is currently building a giant fiber-optic instrument called VIRUS as part of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). VIRUS will use 34,000 fiber optic cables bundled into 150 bunches like the one pictured at the top of this article. In a single pointing of the telescope, VIRUS will take a spectrum of everything in a region of the sky a bit smaller than one tenth the area of the full moon. Over the entire HETDEX experiment, several thousand of these exposures will be taken, adding up to an area of sky roughly as big as 500 full moons! This experiment would be impossible without fiber optics.

Fiber optics are also used to take light from the telescope and send it into an instrument housed in a separate room. Instruments are usually mounted on the telescope itself, and so they get jostled and turned (sometimes upside-down!) as the telescope follows objects across the sky, and the instrument can even change size slightly as the air around it cools off during the night. With careful engineering, those jostles and rotations and thermal contractions can be minimized so that the camera is quite useful. But some science, like looking for Earth-sized planets around other stars, requires a much more stable instrument. So, with fiber optics, we can build the instrument in a temperature controlled room that is isolated from the bumps and wiggles of the telescope, and send the light from the star to that room. Such instruments are among the most precise astronomical tools now in use, and were used to measure the tug of a planet only twice the diameter of the Earth on its parent star.

So, in short, modern astronomy owes a lot to all of this year's Nobel Prize winners. Congratulations and thanks to Drs. Kao, Boyle, and Smith!

And the Nobel Prize for Physics Gadgets With Huge Astronomy Impact Goes To...

2009-10-06T10:28:00.000-05:00

Many people will be blogging today about today's announcement of the 2009 Nobel Prize in Physics, what the awards are for, who did what, and who didn't get recognized that should have. so I thought instead I'd focus on the astronomy aspects of today's awards, which are very important. First, one paragraph on today's awards.

This morning, the winners of the 2009 Nobel Prize in Physics were announced. Dr. Charles Kao won half of the prize for making some tremendous contributions in fiber optics that led to their usefulness for communication. (Contrary to some reports I've read, Dr. Kao did not invent fiber optics; he and his collaborators found a means to allow fiber optics to send messages over long distances, necessary if you want to make a phone call via fiber optic cable across a continent or ocean.) Dr. Willard Boyle and Dr. George Smith jointly received the other half of the award for their work on charge-coupled devices (CCD), which are one of the major types of digital cameras. Most cheaper digital cameras, including, most likely, any that you own, use a different type of digital imager called CMOS (read here to learn about the difference), but the CCD has traditionally provided better images and better sensitivity.

Both of these achievements have had crucial impacts on astronomy. Today, below the jump, I'll talk about the CCDs, and tomorrow I'll talk about fiber optics.

The CCD is an electronic device that works on a principle for which Einstein won a Nobel Prize in 1921 called the photoelectric effect. When light hits some kinds of metal (like silicon), the light is absorbed and an electron, that tiny electrically-charged particle that is the basis of electricity, is released. Einstein's award came because he realized that the photoelectric effect could be explained by light acting as a particle (which we call a photon). An electron in an atom of silicon can absorb a single photon and be freed from its bounds to the atom. Add a little circuitry, and you can even make an electric circuit. This is the basis for photovotaic cells (solar panels that produce electricity).

Another thing that Einstein realized was that the number of electrons released was equal to the number of photons absorbed. In other words, if you could count how many electrons were released by a piece of metal, you know how many photons hit that piece of metal and were absorbed.

A CCD is, at its simplest, a device that has a bunch of little pieces of metal (usually silicon) arrayed in a grid. An image can be focused using mirrors or lenses on this grid, and each of the little pieces of metal (let's call them picture elements, or pixels for short) counts how many photons hits it. Then some more circuitry counts the number of photons in each pixel, and you can reconstruct the image. If you then make a little computer file that keeps a record of how many photons were in each pixel, you can reconstruct the image on your computer months or years later. And you can send that information (by radio waves, by the internet, even by Morse Code through fiber optic cables) to anybody else, so everyone can see your image. In other words, a CCD can be used as a digital camera. Neat!

In astronomy, CCDs have replaced photographic film as the primary way of detecting light from astronomical objects. The reason for this is pretty simple. Since we can count how many photons came in from a star, planet, nebula, or galaxy, we have a better record of how bright that object is. We can also be clever by using filters or prisms to split the light into the colors of the rainbow, and then we can count how many photons we get in different colors of light. Photographic plates also record how much light you get, and you can play the same tricks with filters and prisms, but they don't provide a hard number count of the number of photons. In physics and astronomy, the best science requires hard numbers. CCDs win.

CCDs also took over because they provided digital information that could be stored on computer disks and easily duplicated and shared with collaborators and with the world. Photographic plates can be duplicated, but it is a hard process to do that without losing information (ever see a photocopy of a fax of a photocopy?).

Another big advantage of CCDs over other types of imagers, including other types of digital imagers, is that CCDs are very efficient. A well-made CCD can turn 95% or even more of the photons that hit it into electrons, and they can have a pretty uniform efficiency over the entire camera. Even more important, the efficiency is repeatable, so even if one corner of the camera doesn't detect light as much, you can use calibrations to calculate exactly how efficient each pixel is, and so you can correct for efficiency differences. The sensitivity of photographic film can vary from one batch to the next, and even from one frame to the next.

For these reasons and others, CCDs are the workhorse instrument of astronomy. If you go to any opticla observatory, look inside the Hubble's cameras, or look into X-ray and ultraviolet telescopes in space, you'll find a CCD at the heart of the vast majority of cameras. Those cameras that use other detectors usually have special design needs.

There are some important places in astronomy where CCDs do not rule. These include the highest energy light (gamma rays) and the lowest energy light (radio waves, microwaves, and much infrared light). At the high energy end, silicon is transparent. The gamma ray photons are so energetic they just pass right through silicon without leaving a trace. For radio waves and other low-energy types of light, the energy in a single photon of light is not enough to free the electron from its parent atom, and so the photoelectric effect doesn't work. In the infrared, there are imagers related to CCDs that can use special materials that still use the photoelectric effect, but in microwaves and radio waves the individual photons are just far too puny. At those wavelengths of light, we use antennas to detect the photons' wave-like nature.

Help astronomers support public education in science

2009-10-02T10:08:00.000-05:00

When my daughter started school, I was shocked to learn how dismal the funding levels for public education truly are in much of the country. Every year, teachers send home wish lists asking for donations of supplies for their classrooms; if these items are not donated, the teacher has to pay for them out of her already meager salary. And we're not talking about "luxuries" like computers and other technology, we're talking absolute basics: pens, pencils, paper, even Kleenex. What kind of country is this where we have to ask teachers to buy Kleenex for their students?? It makes me livid every time I think about it. And, with the current bad economy, classrooms are being squeezed even more than normal.

Anyway, the folks over at the Cosmic Variance blog (another astronomy and physics-related blog run by some darn good scientists) are participating in a friendly fundraising competition run by DonorsChoose. DonorsChoose allows people to donate money directly to individual classroom projects in public schools in the United States. Basically a teacher proposes an activity, asks for the money she/he needs to do the activity, and you get to choose which activity you want to help fund. Since they're all scientists, the Cosmic Variance folks have identified several science-related projects, and are trying to raise more money for these projects than other teams.

In short, you can directly further American science (and/or non-science-related) education by donating as little as $5, and also help a small band of astronomers win a friendly competition. To donate money for the Cosmic Variance team effort, click here. To read more about DonorsChoose, to start your own team, or to choose non-science related projects to donate to, look here. And, lastly, encourage people you know to give what they can.

The sausage making of science

2009-09-28T10:58:00.000-05:00

I have one last week of serious telescope proposal writing that will likely keep me from blogging very much. In the meantime, here's an article by planetary scientist Dr. Mike Brown about some of the problems with doing science. As I've said before, science is not devoid of emotion and egos, as much as we'd like to pretend it is. I'm unfamiliar with the papers in Dr. Brown's article, so I don't know who's right scientifically. All I can say is that these issues pop up much more often then I'd care to see.

Book Review: Backyard Guide to the Night Sky

2009-09-22T22:09:00.001-05:00

I've been a subscriber to National Geographic magazine for many years, and I've always been impressed by the quality of that publication and other productions by the National Geographic Society. So, when I was asked if I would write a review of their new book, Backyard Guide to the Night Sky, I was tickled pink and jumped at the opportunity.

The book I received (cover shot above) is a paperback, roughly eight inches tall and five inches wide. It's easy to carry around, and the pages are a fairly heavy stock, similar to other high-quality field guides I have from the Audubon Society. I wanted to test and see how the pages hold up to damp conditions like backyard astronomers might experience on a dewy night, but due to the ongoing massive drought here in Austin, I didn't have such a night for a test. However, it did rain about a week ago, so I sat outside (under a porch) and read for about an hour with no noticeable effect on the book. I did notice that my fingers would leave prints on some of the black pages in the book, but these prints disappeared within a few minutes. The numerous prints, photographs, and illustrations were all sharp with vivid colors. So, the overall impression I have is that this is both a beautiful and durable book.

The layout of the book struck me as fairly clever. The book is split into ten chapters that cover both the science of astronomy and the basics of observing that any beginner wants to know, from the very basics on learning the night sky, to the planets of the solar system, to a description of individual constellations, to discussions on types of equipment the beginning astronomer needs. Within these chapters, a different topic is covered on every two facing pages. I found this a very nice feature. Only have a couple of minutes? Read the next page in the book, and you'll get a complete thought. Or if you want a quick bite of a random area of astronomy, just open the book and start on the upper left of any page.

The portions of the book covering amateur astronomy contain some unique features I haven't seen in other books (though keep in mind I haven't read any other astronomy guide book for at least 15 years). There are tips for sharing the night sky with children, including points that I wouldn't have thought of on my own, such as how just hearing stories of constellations will likely be far more satisfying than spying a distant, faint galaxy through a telescope. The discussions of astronomical equipment are also up to date, covering topics such as digital cameras and computerized telescopes. A chapter on the seasons of the sky points out striking star patterns visible during each season, a very useful topic for beginners who are frustrated when they can't find Orion on a balmy summer evening (Orion is a winter constellation).

However, this book does have some deficiencies. I was disheartened by a number of minor scientific inaccuracies throughout the book. For example, in a discussion on the composition of the sun, the claim is made that the sun's core is composed of 92% hydrogen, 7% helium, and trace amounts of the other elements. The following sentence then claims that the outer layer of the sun has "substantially more helium": 25%, with 74% hydrogen and trace amounts of other elements. In reality, the composition of the core and outer parts of the sun are virtually identical; the first set of numbers (92% hydrogen, etc.) is the sun's composition if you look at numbers of atoms, while the second set of numbers (74% hydrogen, etc) is what you get if you look at the relative masses of the various elements in the sun. Most every science section has at least one minor error or slightly misstated fact like this. Now, you might consider this nit-picky, and maybe it is. It's not as if the book makes egregious errors like claiming that Pluto is the largest planet in the Solar System (which I actually saw once in a video) or that the stars are powered by billions and billions of hamsters running in little wheels. But I expect a higher level of quality out of National Geographic than I would from other publishers, and these little errors don't meet my expectations.

There are some errors on the backyard astronomy aspect of things, too. For example, the Summer Triangle (made up of the bright stars Vega, Deneb, and Altair) is one of the easy ways to learn your way around the summer night sky, and the book makes that point very clearly and correctly. This point is illustrated by a photograph of the summer sky and with the stars of the Summer Triangle labeled. Except every single one of the stars is mislabeled. One of the labeled stars isn't even in the Summer Triangle. Oops. And, while the magnitudes of stars are given throughout the book, I didn't find the fairly important concept of magnitudes explained. Perhaps I just missed that page, but there's no reference to magnitudes in the table of contents or the index.

Finally, let me make a few other random notes. First, this book is written for people in the northern hemisphere. While a few mentions of the absolutely marvelous southern skies are made, this book is not appropriate for the beginning astronomer south of the equator. The photographs and illustrations are numerous and quite vivid, but the captions are usually quite terse; I often found myself asking, "Which star cluster is that?" or "Which satellite took that picture?" Lastly, the authors make an obvious effort to try and refer the reader to a variety of astronomical websites, but there are some glaring omissions. For example, under a listing of websites of national and international astronomical organizations, there is no mention of the American Astronomical Society, the Astronomical Society of the Pacific, or the American Association of Variable Star Observers, three of the major astronomy organizations in North America. It's not reasonable to expect a comprehensive list of websites, books and museums, but the listings are rather sparse and somewhat random.

In short, I'd say the Backyard Guide to the Night Sky is a well-designed and beautiful book with several novel concepts, a layout useful to even the most short-attentioned person, and a slew of useful information for the beginning backyard astronomer in the northern hemisphere. This is also a fine book to encourage a general audience to go out and enjoy the wonders of the night sky while learning a little science along the way. However, the book is in need of careful scientific editing, as there are a number of (generally minor) scientific errors throughout the book. This is disappointing, and for this reason I don't believe the current edition of the book is appropriate for those who can already find their way around the sky and may be looking for a more in-depth look at the science of astronomy.

Backyard Guide to the Night Sky
by Howard Schneider
ISBN 978-1-4262-0281-0
Cover price: US $21.95 / $26.00 CAN

Data, Analysis, and Reality

2009-09-17T20:56:00.002-05:00

As a scientist, I must always struggle to remember the difference between actual data and inferences based upon those data. This difference is often pretty clear. For example, if I take a picture of a star cluster, the actual data I've collected are counts of the number of photons arriving from different parts of the sky. I then infer that an excess of photons coming from a single point is a star, while an excess coming from an elongated smudge is likely a galaxy. My data are counts of photons, and my inferences are the nature of the object. Clear enough.

Sometimes the line is blurrier. For example, suppose I take a spectrum of the light from a star, where I split the light into its component colors. Typically, I see light from many colors of the rainbow, with perhaps a few specific colors missing (see some examples here). Those missing colors are due to individual elements, like hydrogen, helium, or oxygen, absorbing that light. Most often, that light is absorbed in the atmosphere of the star I'm looking at, and there are diagnostic tools that I can use that look at the lines and tell me the temperature of the star and how much of the given element exists in that star.

A few years ago, I wrote a paper on spectra of a group of white dwarf stars. I noticed that about one quarter of the white dwarf spectra showed the fingerprint of calcium. Calcium is an element that is very easy to see in stars, and it usually indicates the presence of many other elements, like iron and magnesium, that are not as easy to see. This is interesting, because the gravity of white dwarfs is so high that elements heavier than hydrogen and helium should sink out of sight below the stars' surfaces in a matter of years. Those white dwarfs with calcium and other heavier elements must therefore be swallowing this material from somewhere, and there's good reason to think that this material may be from asteroids or comets, the remains of solar systems around these dead stars. So, did 1/4 of my white dwarfs once have planets?

Sadly, the answer is no. I was seeing calcium, all right, but it wasn't in the star. It is probably mixed in with the interstellar gas that occupies the mostly (but not fully) empty space between the Earth and the white dwarf. In the meantime, I'd gone around proclaiming that the "data" showed there was calcium in the star. But my real data were just the number of photons of different colors of light, my spectra; the rest was just interpretation of what I was seeing. And my interpretation was not correct.

In the past couple of days, a couple of astronomy news stories have made the rounds that show that I'm not the only person who confuses data and interpretation. One story involves a cold spot in the Universe. The WMAP satellite has spent five years measuring the temperature of different parts of space using microwaves. Most of the Universe is about 3 degrees Kelvin, the "echo" of the Big Bang, but some parts are a little hotter and some a little cooler. Some of those hot and cool spots are relics of the earliest seeds of galaxies in the Universe, while others are caused by structures in space between us and the distant reaches of the Universe from whence these microwaves came. If the microwaves travel through a bit of space that has more matter than average, they tend to heat up a bit. If the microwaves travel through an empty part of space, they tend to cool off a bit. The technical term for this is the Integrated Sachs-Wolfe Effect.

So, WMAP measured the temperature of each part of the sky. In one part of the southern hemisphere sky, there is a cool spot. Initial indications were that this spot was much cooler than any spot we would expect in the Universe. In fact, to get a spot this cool would require an absolutely humongous empty void of space, a void so large that the Big Bang theory says shouldn't be possible. Had astronomers discovered evidence of a problem with the Big Bang theory? Over the past five years, at least 125 papers have been written that talk about this cold spot. Some just mention it, but many do detailed studies of its shape, temperature, and how it means that exotic physics, like cosmic membranes or superstrings or "textures" or "domain walls" or even portals to other Universes exist at that point in the Universe.

However, there are some people who claim this cold spot is not real. A new paper by Ray Zhang and Dragan Huterer, physicists at the University of Michigan, claims that the spot is, in fact, an artifact of the way the data were analyzed. WMAP indeed found a cold spot in the Universe, but that doesn't mean that the cold spot is a giant void. The huge void is an interpretation of the data when the data are analyzed in a certain way. Analyzed another way, the cold spot could just be a normal-sized void, of which there are many in the Universe, and all of which are expected by the Big Bang theory. I don't think that this paper is the final word; we observational astronomers just need to go and look at the cold spot with other wavelengths of light and see if there's anything there. That will settle the issue. But, again, before we go tossing the Big Bang theory and searching for cosmic textures, perhaps we need to remember what is data (a cold spot in the microwave sky) and what is inference (superhuge voids).

The other story making the rounds where data and inference are being confused by some is yesterday's announcement that European astronomers had determined that one planet around another star, CoRoT-7b, is the first rocky planet found outside our own Solar System.
First, let's look at what we know for certain (or at least can infer with a high degree of certainty). The parent star, with the horrible name of TYC 4799-1733-1, is a pretty normal star. Last year, a satellite called CoRoT was observing this star, and saw the star dim slightly every 20.4 hours. This dimming is consistent with a planet that has twice the diameter of the Earth orbiting the star once every 20.4 hours! (For comparison, the Earth goes around the sun once every 365 days, and the hot little planet Mercury goes around the sun once every 88 days.) Such a planet is very, very close to its parent star, would be blasted by the star's light, and would be a horrible place to visit.

Since its discovery, scientists have been measuring the spectrum of the parent star with a very sensitive spectrograph at the European Southern Observatory in Chile. The spectrum shows that the star is moving back and forth very slightly every 20.4 hours, indicating that the star is being pulled ever so slightly by the planet's gravity. The astronomers have made an amazingly precise measurement, finding that the star moves back and forth at a speed of 12 kilometers an hour ( 7.5 miles per hour). I can run faster than this star moves, and yet we humans can measure that speed from 500 light years away. Just amazing.

Anyway, from that motion, we can use Newton's theory of gravity to calculate the mass of the planet, and it is about 5 times the mass of the Earth. And, since we know the planet's mass, and since we know its diameter, we can calculate its average density. That density is 5.8 grams per cubic centimeter, almost exactly the same as the Earth.

Let's review: the data we have are the number of photons from the parent star we detect on Earth over time, and the spectra of the star taken over time. Very careful data analysis allows us to infer (though with a very high degree of confidence) that the periodic dimming of the star is caused by a planet with a diameter twice that of the Earth, that the star is moving in response to the planet's gravity, that the planet must be five times the mass of the Earth, and that the planet's average density is similar to that of the Earth.

Next, the astronomers claim that this means that the planet must be made out of rocky material, just like the Earth. I think this is probably right, but it isn't as certain. We don't have pictures of the planet, showing that it is made out of rock. It is possible to dream up weird mixes of materials such as iron, rock, water, and/or gases that could give you a planet with the same diameter and mass as CoRoT-7b, but these are pretty contrived. In our Solar System, all the planets with density similar to that of the Earth all are made out of rocks. And, when we look at newly-forming planetary systems, we see signatures of rocks and rock-like dust. So, it seems very likely that CoRoT-7b is made out of rock. But this is not a proven fact; it's a supposition, an inference. We don't know for certain that this planet is made out of rock; that is just the most reasonable explanation we can think of right now.

Further, many of the news stories (notably not the original press release) imply that this means that the planet is solid, or has a solid surface. Again, the planet may well be solid. But we really have no clue. The part of the planet that faces its parent star could be as hot as 2000 degrees Celcius (3600 degrees Fahrenheit) -- hot enough that Earth-like rocks would be molten. The back side of the planet could be cold enough for water ice to form. Could there be a planet with a surface that is half lava, half ice? Or the planet could have some sort of thick atmosphere that gets denser until it just sort of merges into a solid or liquid state, though it is hard to imagine how a planet could hold on to an atmosphere at those temperatures. We don't know. We don't really have a clue. We just have educated guesses of what sort of surface such a planet could have.

So, again, let's remember to separate what we know (a planet about twice the diameter of the Earth, five times the mass of the Earth, and a density similar to that of the Earth) from that which we can only infer very indirectly, such as what the planet may be made out of and what its surface may be like. As we find more and more Earth-sized planets (and I am confident that we will find Earth-sized planets very soon), and as we find Earth-sized planets in orbits far enough from their parent star to be similar to Earth's orbit, we have to remember that we will know very little about what those planets are actually like. Do they have atmospheres? Do they have liquid water? Do they have life? Answers to those questions are likely still a decade or more away. In the next few years, all we will know are the diameters and masses of any Earth-sized planets. The rest will come. But we'll need real data, not inferences.

Looking for Planets Around White Dwarfs

2009-09-14T16:46:00.003-05:00

Image Credit: NASA / JPL-Caltech Our Solar System is such a nice, ordered place. Eight (or nine or thirteen) planets have been happily circling our sun for 4.6 billion years, and the whole system is stable enough to life to have formed on at least one planet. And the solar system looks like it will continue to be a nice, stable place to live, at least for another six billion years. At that time, the sun will run out of hydrogen fuel, swell up into a red giant star (swallowing Mercury, Venus, and maybe Earth in the process), expel about half of its mass as a planetary nebula, and then shrink into a white dwarf. When the sun loses mass, its gravitational pull will weaken a little. This will cause the remaining planets to move outwards in their orbits a little bit, but they should remain bound to the white dwarf sun, forever circling the ashes of our star.

Now that we astronomers are finding planets around all kinds of stars, we can estimate that at least ten percent of stars have planets of some sort. Many of these planets are very close to their parent star, much closer than Mercury is to our sun. But many are further away, like Jupiter. And, like Jupiter, these planets should survive the death throes of their parent star, and be circling white dwarfs.

Here at Texas, my colleagues have been looking for planets around white dwarf stars, with only one possible success so far. It's a long, hard, slow process that involves looking for the gentle tug of gravity that the planet exerts on its parent white dwarf.

Another of my colleagues, Dr. Mukremin Kilic of Harvard University, has been looking for white dwarf planets another way. He's trying to detect the infrared light given off by giant planets, a heat left over from the very creation of those planets. A newborn giant planet can be as hot as a few thousand degrees on its surface, and even Jupiter still glows at a more feeble one hundred degrees Kelvin (a modest -300 degrees Fahrenheit). With an infrared light telescope, it may be possible to detect these planets around white dwarf stars.

Today, Dr. Kilic released a study that he and his collaborators completed using the Spitzer Space Telescope to look for extra infrared light coming from 14 individual white dwarf stars. They specifically targeted white dwarfs that came from stars three to five times more massive than the sun. This is because astronomers have noticed that bigger stars tend to have bigger planets, and that bigger stars don't live very long. That means that any planets around these stars should be bigger and brighter (because planets cool over time). They found no evidence for any planets.

Does this mean that white dwarfs just don't have planets? Not necessarily. Even though Kilic looked at what should be fairly bright and young planets, he and his team were still limited to finding planets about five times the mass of Jupiter. Planet searches around living stars have found that these behemoth planets are rare; it's more common to find smaller planets than bigger ones. Also, more massive stars become larger red giant stars, and so they can swallow planets out to much larger distances. While the Earth may or may not survive a red giant sun, Jupiter might have trouble surviving around a star five times the mass of the sun.

And perhaps Kilic and his collaborators may just have gotten unlucky. Roughly 10% of stars have planets, and they looked at 14 stars, so they might have only expected 1 star to have planets. And, in the funny way that statistics work, expecting one and finding none doesn't prove very much. But, this isn't the first work on planets around white dwarfs that Kilic has published; he and his collaborators have now searched about 40 white dwarf stars for planets, so they might have expected to find four. If you expect to find four planets and find none, then you may be on to something.

There's another possibility. Many planetary systems we find tend to be chock full of planets. Our own Solar System has four giant planets. Remember how I said that when the sun loses mass, the planets will move a little further away? In that process of moving away, it is possible for the planetary orbits to become unstable, and one or more planets could be flung out of the system. So, maybe big planets won't be found around white dwarfs because of this. We don't know.

Astronomers today are finding planets everywhere, and we do expect to find them around white dwarfs, too. But studies like Kilic's are showing that these remnant solar systems, fossils of planetary systems once similar to our own, are not easy to find. Perhaps they are just harder to see than we thought. Perhaps they didn't survive the death of their parent star. Time will tell. If nothing else, we just need to wait six billion years and watch what happens to Jupiter, Saturn, Uranus and Neptune. One way or another, we'll learn what happens to planets when their parent star dies.

New Hubble pictures!

2009-09-09T16:28:00.003-05:00

Image Credit: NASA, ESA and the Hubble SM4 ERO Team

Yes, I know I'm a whole 6 hours late to the game in bringing you these photos, during which time every other science-related blog in the world already posted them. But they are just so cool, I'm going to post them anyway.

Last May, the space shuttle Atlantis visited the Hubble Space Telescope for their fifth and final servicing mission. Hubble has certainly been one of the crowning achievements of NASA and the Space Shuttle program; the astronauts transformed a dud of a telescope into one of the most important astrophysical laboratories ever built. In May, astronauts replaced two instruments and repaired two others, plus gave Hubble new batteries, gyroscopes and some other minor repairs. Today, after nearly five months of sometimes frustrating checkout and calibration, NASA released its first images from the repaired Hubble.

You can look at all of today's images here. There are pictures of the colorful center of the Milky Way Galaxy's biggest globular cluster, omega Centauri. That picture shows the power of Hubble. From the ground, the center of omega Centauri looks like a blob of starlight, there are so many stars! Yet Hubble resolves them all. The Hubble also imaged the birth of a new star and the death of an old one.

For those of you who can speak spectra (the splitting of light into its component colors), there are some amazing spectra from the uber-massive star eta Carinae (a star nearly 100 times the mass of the sun, about as big as any single star can get!), spectra of gas near a supermassive black hole showing changes over the past 10 years, and more. While spectra are often less inspiring for the general public to look at, they carry far more information than you might guess. From a spectrum, we can determine the speed of a moving object, its atomic composition, its temperature, its atmospheric pressure, and other important quantities that a picture alone could never tell.

My favorite image (and the one at the top of this article) is of Stephan's Quintet, a tight grouping of five galaxies. Four of the galaxies (the yellowish ones) are located 290 million light years away and are so close together, gravity is ripping off pieces of the galaxies, creating streams of stars and rings of new star formation. The fifth galaxy, the whiter one in the upper left of this image, is not related to the others. It is only 40 million light years away, and just happens to be along the line of sight to the other galaxies. Just think -- when the light that Hubble saw left the more distant quartet of galaxies, the first dinosaurs were just starting to roam the Earth. When that light passed the closest galaxy, dinosaurs had already been dead for 25 million years, and the earliest humans were still 38 million years away. But the neatest part of this image is the zoomable version, so you can zoom in and around the image to see amazing details. You can see individual stars in the closest galaxy! Cool stuff.

Anyway, Hubble is now doing hard core science again (and has been for a few weeks). Thanks once again to the amazing team of astronauts and ground crew for fixing this marvelous telescope!

Note: At times I've been getting some errors when trying to access views of some images. If this happens to you, take a deep breath and try again. They must be popular!

News tidbits

2009-09-08T17:22:00.003-05:00

It's telescope proposal time again, so I'm spending much of my day and energy writing short applications to use various telescopes. I'll take an easy path out here and just post some news snippets.

Refurbished Hubble pictures come out tomorrow! It's hard to believe that the most recent and final Hubble Space Telescope repair mission was four whole months ago. Tomorrow, NASA will officially release its first pictures from the refurbished telescope (if you don't count those pictures of Jupiter from July). I've been seeing some colleague's new Hubble pictures for several weeks now, despite threats from NASA that they'll never get Hubble time again if they show the pictures. Astronomers can't keep secrets, even when dire threats are made. Anyway, Hubble is now mostly doing science again, with some final calibration and engineering activities filling up the rest of the its time. If you want to see the release of the new images, check out NASA TV at 11am EDT (8am Pacific, 15:00 UT).
NASA's Review of U.S. Human Space Flight Plans Committee's Summary Report is out. This was a committee charged with reviewing NASA's future plans for manned space flight. A description of the committee and a link to the 12-page summary itself can be found on this page. The two major findings are (a) that the shuttle program will have to rush to finish its current launch program by the end of 2010, potentially risking safety, so NASA should be given some funding to allow the schedule to expand into the first half of 2011, and (b) that, at current NASA budget levels, the International Space Station (which isn't even finished being built yet!) will have to be de-orbited in 2015, NASA's newest Ares rockets will not be ready until at least 2016, and that a return to the moon could not happen before 2030. The committee also outlined several options where, for an extra $3 billion / year, the space station can be run to at least 2020, and missions to the moon or other near-Earth places could begin in the early 2020s.
Neil Armstrong admits the moon landings were faked. Or not. Last week, the satirical newspaper The Onion published an article claiming that Armstrong had been convinced by a conspiracy theorist that he had not, in fact, landed on the moon (warning: the Onion often contains adult language). Evidently some foreign newspapers, not realizing that the Onion is satirical (i.e., it makes everything up), picked up the story and unknowingly presented it as real. This just goes to show that you shouldn't believe everything you read. Not even on the Internet.

Happy New Year!

2009-09-01T18:09:00.002-05:00

It's the start of a new school year here at the University of Texas. The building is full of freshmen wondering why the elevator doesn't stop at certain floors, our large number of weekly seminars are starting up again, and we've welcomed a dozen or so new graduate students into our program, and we're awaiting the arrival of a new faculty member and a few new postdocs.

Life in academia is centered on the school year, not on the calendar year. And, because of the incredibly slow bureaucracies common at universities, it's already time to start thinking about applying for money and jobs that would start next September.

For the past three years, my position here has been financed by a fellowship from the National Science Foundation. That money enabled me to expand my research programs, explore new and exciting areas of astronomy, and spend a lot of time writing blog posts and surfing the astronomy internet. That changed at the stroke of midnight last night, as my research fellowship came to an end.

In reality, there's not much change for me in the short term. For the next several months, I'm getting paid out of a different research grant from the National Science Foundation. It means a slight pay cut and some new research responsibilities, but otherwise few changes. I'll still be blogging as I can, I'll still be studying white dwarfs, and I'll still be looking for that ever-elusive permanent, tenure-track position.

So, sit back, relax, and enjoy the ride. With the start of a new year, the possibilities seem endless.

Help astronomers understand the weird star epsilon Aurigae

2009-08-26T14:16:00.005-05:00

By Nico Comargo and courtesy www.citizensky.org The star epsilon Aurigae is one of the most mysterious objects that you can see without the need for a telescope. With your eye, it looks like a pretty normal star in the constellation Auriga. But every 27 years, it gets noticeably fainter for almost two years, then it returns to its normal brightness for another 25 years. And the cool thing is, nobody is really sure why (read an older post of mine for a little more info, or read articles on this star in the May 2009 issue of Sky and Telescope (click here for the PDF version of the article) and in the October 2009 issue of Astronomy magazine.

Epsilon Aurigae is just beginning its first eclipse since the early 1980s. In order to better understand this system, a large team has been assembled by the American Association of Variable Star Observers, Denver University, Adler Planetarium and Astronomy Museum, Johns Hopkins University, and the California Academy of Sciences.

Best of all, this team wants and needs your help to study this weird star! As part of the International Year of Astronomy, the CitizenSky project has been created to recruit, train, and coordinate public participation in the study of epsilon Aurigae. It doesn't matter whether you have a PhD in astronomy or whether you wouldn't know which end of a telescope to look through, you are heartily welcome to help. (If you have a PhD in astronomy and still don't know which end of the telescope to look through, that's okay, too! It means you're a theorist, and you can probably come up with 30 new explanations for epsilon Aurigae for observers to test in the coming year.)

CitizenSky got a big boost earlier this week when it received three years of funding from the National Science Foundation for the project. So, instead of worrying how to pay for everything, the organizers can focus on getting the best science, instead.

Some professional astronomers will be studying epsilon Aurigae with big telescopes, too, but we can't look at the star 100% of the time for the next two years. In fact, the biggest telescopes can't even look at the star, because it is too bright. And, besides, there're other neat things going on in astronomy, too! So if epsilon Aurigae does anything unexpected, especially on day-by-day or even hour-by-hour basis, there's a good chance professional telescopes won't be looking. This gives you the chance to be the one making observations of epsilon Aurigae when something cool happens.

In order to succeed, CitizenSky needs your participation and help. If you have a nice telescope with some digital imaging equipment, great! If all you have is two eyeballs and a scrap of paper, that will work too! Just click on over to CitizenSky.org to read more about the project and how you can contribute valuable data to help solve the mystery of epsilon Aurigae.

And, if you know anyone else who might be interested, spread the word!

More thoughts on Pluto and the scientific method

2009-08-25T18:00:00.004-05:00

While ruminating on my post on Pluto and the definition of planets yesterday, I thought of a couple other points on the topic that I wanted to make, though not necessarily related.

1. The story of the status of Pluto is a great illustration of the scientific method. The discussion of the discovery of Pluto, the much later discovery of the Kuiper Belt, and Pluto's subsequent demotion is (with one big exception I'll get to in a couple of paragraphs) an excellent illustration of the way that science actually works. When new data comes to light, we should never be afraid to re-examine even the most dear of scientific ideas. No matter how much we love Pluto (and it's okay to love Pluto, to study Pluto, to spend multiple careers working on Pluto, and to revere Clyde Tombaugh and the amazing amount of work he did to discover Pluto), we have to be willing to reconsider its status. To say, "Nope, it's a planet, end of story" or to say, "Nope, it's not a planet, end of story" is to be unscientific.

Further, science rarely gives us clear-cut answers, especially in the short term. Different teams of excellent scientists can examine the same evidence and come to different conclusions. Only through further study and analysis and debate can the deeper, underlying truths of science be brought out. The discussion of what Pluto is continues (though not always in the public eye), and the vast majority of scientists involved, deep down inside want to know the truth as to what is going on. If you want to learn how science really progresses, keep watching the unfolding saga of Pluto. In the end, the truth will be discovered. It just takes time and lots of work.

2. The International Astronomical Union's demotion of Pluto was far more a decision to solve a bureaucratic nightmare than a decision on the underlying science. Three years ago, the International Astronomical Union found itself with a problem. The IAU has, by consensus of the astronomical community, the final say in the naming of objects. And the IAU has devised specific rules for how to name objects, from planets to moons to asteroids. The rules differ greatly -- planets are named after Roman gods, moons of planets have restrictions also based on mythology, but asteroids ("minor planets") can have many other names, such as the asteroid Misterrogers.

With the discovery of Kuiper Belt objects larger than Pluto, the IAU needed to decide what set of rules the naming conventions should follow. What if someone found a Mars-sized Kuiper Belt Object and wanted to name it Bartsimpson? And which committee in the IAU would get to choose the name? Would the discoverer get a say in the name?

So the IAU decided to create the classification of "dwarf planet" to include all the smaller things that were generally round in shape (the biggest asteroids and Kuiper Belt objects), but were not moons and were not one of the classical planets. This designation allowed the IAU to come up with new naming rules, and everyone could be happy.

This turned into a disaster. What should have been simply a rule on how to name bigger round things turned into a vote on what constitutes a planet. And, as I pointed out yesterday, there are many ways of drawing lines, none of which seems inherently obvious. And this definition went through revisions, and astronomers voted on it. Yet this is not how science works. Scientific truths and laws are not decided by vote. The laws of nature are what they are, and it is our job as scientists to figure out what those laws are over time. This can take years, decades, or even centuries, yet the IAU definition was debated, altered, and approved in a couple of weeks.

I think the IAU should probably just have said something like, "We're making a new class of objects for the purposes of naming conventions. Objects orbiting the sun and large enough to be made round by their own gravity shall be named after mythological gods, and not just Greco-Roman gods, and Committee X has the right to decide how such names are to be selected." That would have solved the naming crisis yet allowed the scientific community to continue to debate exactly what makes a planet, and whether there is a fundamental physical difference between different types of rocky bodies.

Alas, this isn't what happened. They shoulda asked me.

3. What should the role of public opinion and historical precedence be, if any? I'm not going to do much more than open this can of worms, but to what extent can or should public opinion matter? After all, even if 100% of the world's people felt that the moon was made out of green cheese, the moon wouldn't magically transform into a giant Limburger; it would stay a round body made of metal and rock. And if 95% of Americans wrote letters to Congress demanding that Saturn be declared imaginary, and even if Congress passed a law declaring Saturn imaginary, it wouldn't suddenly vanish into the (non-existent) ether. Saturn would continue to circle the sun as always.

So, what should be scientists do about the millions of people still angry about Pluto? We can give in and say, "you're all right, Pluto's a planet." That solution would make people happy, but it completely ignores the scientific process. We could come to a scientific consensus, announce the result, and tell people to "deal with it." That solution would reach the scientific truth (whatever that result might be), but it clearly doesn't work (see point 2 above), and it would really tick off the people who pay our salaries. Maybe we should acknowledge the public's interest in the topic while doing our research, reach a scientific conclusion, and all the while try and teach y'all what we are doing, why, and how we reach the conclusions we do? Nah -- that would be hard. And make too much sense.