Thursday, May 28, 2009

A Request for Observing Suggestions

Image Credit: McDonald Observatory

The past few years, I've blogged about a continuing-education workshop I help facilitate at McDonald Observatory. We have 15 high school teachers from across the country who spend five days learning about stellar evolution and white dwarfs and four nights using our 30- and 36-inch telescopes.

The 2009 version of this workshop is coming up in early July, and I'd like to ask your help in our planning for this year. Does anyone out there has some good suggestions of little-known gems of the sky that we might be able to look at through our big telescopes with our teachers? A few pointers of what we're looking for are below. Just stick your ideas in the comments section.

First, some details on the telescopes. The 36-inch reflector is for eyepiece viewing. It is great at collecting light, but has a limited field of view (less than about 10 arcminutes), so open clusters and large nebulae don't look very impressive. The telescope is great for planetary nebulae, globular clusters, and galaxies. For example, we can easily see the spiral arms and dust lanes in the Whirlpool Galaxy. The 30-inch reflector has a wide-field (45x45 arcminutes) CCD camera with broadband filters, so just about any type of object is a fair target there.

  • We are well aware of the Messier catalog and the 8 or 9 planets of the Solar System, so we'd like suggestions outside of those lists.
  • We already target open star clusters as part of the program, so we don't need open cluster suggestions.
  • Because of the dates (July 9-14) and times (before local midnight) of the workshop observing, the Right Ascension range we can easily target is limited to about 14-22 hours. We're a northern observatory, and the effective southern declination limit is about -30 degrees.
  • Colorful double stars or other tight multiple stars are always popular. Due to the size of the 36-inch, bright colorful doubles (like alpha Her or Alberio) are actually painfully bright, so fainter stars would be even better.
  • Please remember that many of our teachers are not amateur astronomers, so many of them are not impressed in trying to see the faintest possible things. I'm thinking flashy things, like galaxies with dust lanes, or interacting galaxies, or planetary nebulae with unique shapes, or compact emission nebulae with intricate details. If you have an idea for a challenging object for the amateurs we will have in our workshop, feel free to submit it, but please mark it as a toughie.
  • I subscribe to Sky & Telescope, and will have issues from May through August with me, so there's no need to copy ideas from there.
You can see a list of what we've taken pictures of with the 30-inch telescope in past years here. (If you want to look at any of those pictures, feel free, but please read the instructions at the top of that page first. Simply clicking on the links will crash your browser! We're going to fix that, eventually.) The picture of the Eagle Nebula at the top of this post was taken by our teachers with the 30-inch telescope.

Thanks for your ideas! Ultimately, we let the teachers choose what they look at, so I can't promise that we'll look at any given object. But we will give you credit for the suggestions!

For more information on the summer teacher workshops at McDonald Observatory, click here.

Wednesday, May 27, 2009

Messier 82 conducts a covert nuclear test

Radio detection of a supernova in the galaxy Messier 82
Image Credit:
MPIfR (click on the picture for a full and extensive list of credits)

Supernovae are powerful explosions that end the lives of the most massive stars in the Universe. At their peak, supernovae can outshine an entire galaxy. Using the Hubble Space Telescope, we've seen supernovae in galaxies billions of light-years away.

Since massive stars end their lives as supernovae (those with masses at least 7 or 8 times the mass of the sun, depending on the results of my research), and since massive stars don't live very long (less than 50 million years, compared with our sun's lifetime of 10 billion years), we expect to see lots of supernovae in galaxies that are currently making loads of new stars, fewer in galaxies that are making just a few new stars, and no supernovae in galaxies not making stars. And this is what we tend to see.

But there has been one major exception. The "Cigar Galaxy," Messier 82, is a fairly nearby galaxy, and it is making new stars at a prodigious rate. So fast, in fact, that the galaxy appears to be exploding, with hot gas spewing into space. There are many gorgeous pictures of Messier 82, such as these from Hubble. We think that the hot gas is being blown out of the galaxy by dozens upon dozens of supernovae, which should be going off at a rate of one every few years or so. (Our Milky Way has a supernova about every 100 years, by comparison). But there's been a problem. Nobody's seen any supernovae in Messier 82.

Now, we astronomers weren't too concerned by this. A byproduct of star formation is lots of dust, and dust is very good at hiding optical light. Other wavelengths of light, like infrared, X-ray, and radio light can travel right through dust, to an extent, so we knew we either had to look for supernovae in other wavelengths than visible light, or we would just have to wait for one to happen near the edge of all the dust in Messier 82. But since most of the new stars in the galaxy are located deep inside the clouds of dust, we might have to wait a long time.

In April of this year, Dr. Andreas Brunthaler, an astronomer at Germany's Max Planck Institute for Radio Astronomy, was looking at Messier 82 with the VLA. The VLA is a large array of radio telescopes in New Mexico (if you saw the movie Contact, Jodie Fisher's character can be seen listening to the radio signals from these telescopes, something you can't actually do). Dr. Brunthaler was taking high-resolution radio images of Messier 82 in order to study the gas and forming stars in this galaxy, when he noticed something that didn't look right. There was a tiny circle of radio light, shining brighter than the rest of the galaxy, that hadn't been there in the past.

Dr. Brunthaler then looked at data they'd taken in early 2008, and he found the same radio source, only smaller. But there was no source on earlier data. He'd found an elusive Messier 82 supernova! You can see three radio pictures of Messier 82 in the photo at the top of this article. One from 2007 looks normal, the one from 2008 shows a tiny bright dot, and the one from 2009 shows the larger bright circle.

More work determined that the explosion happened around the start of February 2008. Lots of optical supernova searches had pictures of Messier 82 from that time, and they didn't see a thing. Neither did infrared or X-ray observations. This supernova is so deeply buried in the dust and gas at the center of Messier 82 that only radio waves can escape!

Now that we know there are supernovae in Messier 82, and not something weird, we can keep watching for more supernovae in the radio regime. If we can get a good count on how often supernovae occur in Messier 82, we might be able to get a good handle on how fast stars are being made deep in the dust enshrouded center of this galaxy.

Lastly, now the Universe should know that it cannot detect nuclear explosions without us knowing. It is unclear if the United Nations is going to act on this surreptitious explosion or not.

Note: In this article, when I talk about supernovae, I'm specifically talking about the explosions at the end of the lives of massive stars, not another type of supernova that is the explosion of white dwarf stars. That's a completely different kettle of fish. I just wanted to make that clear.

Tuesday, May 26, 2009

Oooh, pick me, pick me!

The blog site 3 Quarks Daily has announced a new blog writing prize. For their first go-around, they are awarding prizes for science blogging!

If there's a scientific blog entry (from, say, this blog, or any other blog) that you think is worthy of recognition, please feel free to nominate it! Rules are listed here; primarily, it needs to be an entry written on or after May 25, 2008, and nominations end at the stroke of midnight on June 1.

I won't be doing any self-nomination, because (a) I don't like doing that, and (b) I'm a horrible judge of my own material. But if you feel I actually wrote something pretty darn good, feel free. I only ask that you don't tell me, so I don't feel crushed when Phil Plait wins yet more (well-deserved) recognition.

The Copernican Principle

This weekend I relaxed and caught up on some recreational reading, finally getting through my stack of magazines from April. Now I know why the magazines in so many doctors' waiting rooms are so old; it takes the doctors months to get around to reading them in the first place.

In the April issue of Scientific American, there is an article by Timothy Clifton and Pedro Ferreira pondering if dark energy really exists, or if we perhaps live in the middle of a billions of light-years wide void. A void is a region of space where there is less matter than average, therefore the force of gravity would be less than on average, so the expansion of the Universe would appear to be faster than we would expect, which is just what we see with dark energy. (For what I think is a simple and honest explanation of dark energy, listen to or read the May 12 episode of the 365 Days of Astronomy podcast.)

The authors of the article do what I think is a very good thing: they present a pretty balanced review of both sides of the argument for and against giant voids. One of the arguments against a giant void is that it would appear to violate the Copernican principle.

The Copernican principle is one of the primary pillars of the science of astronomy. It says simply that we do not occupy a privileged location in the Universe. As you might guess, the principle comes out of the Copernican view of the Solar System, that the Earth is not the center of the Solar System, the sun is. In other words, we are not the center of the Universe, but rather we are just a small part in the larger whole.

The Copernican principle has been invoked many times. When astronomers first started to make maps of the Milky Way galaxy, the Sun seemed to be very close to the center (see, for example, this map by famed astronomer William Herschel). This raised alarm bells among some astronomers, because the Copernican principle said we shouldn't be someplace special, and the center of the entire galaxy would certainly seem like a special place, especially since we didn't know that other galaxies existed. This issue was resolved when Harlow Shapley, a great early 20th-century astronomer, used globular clusters to show that we were not at the center of the Milky Way, but way off to one side.

Barely had that crisis been resolved when a new one arose. Astronomer Edwin Hubble discovered that almost every galaxy in the Universe was moving away from the Milky Way, and the further away it was, the faster it was moving. This would seem to put the Milky Way at the center of the Universe, which is again against the Copernican principle! This conundrum was solved when it was recognized that the entire Universe was expanding. In an expanding Universe, no matter where you are, it looks like every other thing is moving away from you. (This is one of those concepts that is hard to grasp; the time-tested "raisin bread" analogy seems to work best, though since many people these days have never seen a loaf of bread rise, a balloon analogy also helps.)

So, back to the voluminous void from the article. For the void explanation of dark energy to work, the Milky Way would need to be located at almost the exact center of a gigantic void. How big? The void would need to be a large fraction of the observable universe! So, we would need to be near the center of a structure that is a good fraction the size of the observable Universe. That doesn't sit well with the Copernican principle. This argument alone doesn't rule out a giant void (the authors admit to many other problems with the void idea), but it makes it hard to swallow.

But I do think we need to be careful in applying the Copernican principle. The principle can be taken too far. For example, we see lots of stars near the center of our galaxy. If any of those stars harbor life-bearing planets, then any intelligent creatures on those planets will find themselves at the center of a galaxy. It's only when they discover other galaxies that they would realize they are not in a special place.

Likewise, if there is a giant void in our Universe, some galaxy will likely be near the middle of it. And if there is life on a planet around a star in that galaxy, they will find themselves in a fairly special place in the Universe.

In summary, the Copernican principle is one of the primary philosophical underpinnings of the science of astronomy. It is not physical law in and of itself, but it does require us to use an abundance of caution around any hypothesis that requires us to live in a special place of the Universe.

The more I think about it, the more I've been imagining the Copernican principle as the Robot from Lost In Space, running around and saying, "Danger! Danger, Will Robinson!" When Copernicus speaks, we should all listen.

Wednesday, May 20, 2009

Another tremendous job by our astronauts

The Hubble Space Telescope has been released back into its own orbit after five grueling spacewalks to perform final repairs. With two new instruments, two repaired instruments, new gyroscopes, new batteries, new pointing equipment, and new insulation, our astronauts have given Hubble the best possible chance for a long continuing career.

This shuttle mission has been fun to watch. I don't get much of a chance to watch most missions, but I can make the excuse that Hubble is part of my job, so my work benefits from watching the repairs to the telescope.

We astronomers often forget that the same astronauts who put so much effort into launching and refurbishing our telescope put the same effort into building and maintaining the International Space Station. Those shuttle missions don't get the same kind of media coverage, probably because installing a camera that can take pictures of the most distant galaxies sounds a lot more exciting than installing a new toilet on the space station. (I'd be willing to bet that the residents of the space station prefer the working toilet.) But the space station work is just as complex, just as demanding, and just as full of trials and tribulations as the Hubble repairs have been. It's very easy, and very unkind, to forget that.

We astronomers tend to gripe quite a bit about the manned space flight wing of NASA. Putting humans into space is incredibly expensive, and we've been unconvinced that the research being done by manned space flight is worth that cost, especially when it means less money for astronomy research. In January 2008, at the winter meeting of the American Astronomical Society, NASA Administrator Michael Griffin challenged us astronomers to, among other things, support manned space flight as much as the manned space flight folks support us. This week, the manned space flight arm of NASA has demonstrated their commitment to the astronomers, by spending years in training, by fighting for this mission in spite of the safety concerns, and by the entire shuttle crew working hard during five long and trying days of spacewalks.

If the problems that we astronomers seem to have with manned space flight are, as I often hear, the lack of a coherent goal for manned flight and a series of science experiments with uncertain scientific value, then it's time for us to stop sniping from the audience and start to offer constructive ideas for the direction of manned flight (and I'm as guilty of this griping and muttering as anyone). The manned space flight program has saved Hubble six times now, counting launch and five servicing missions. They've got our back. Do we have theirs?

Sunday, May 17, 2009

The Agony and the Ecstacy of Space Walking

Today, our astronauts on the space shuttle proved their worth yet again by successfully repairing the Space Telescope Imaging Spectrograph, or STIS, during a long, frustrating, and ultimtely rewarding spacewalk. During the eight-hour marathon, astronauts Mike Massimino and Mike Good had to physically rip a handrail off of Hubble to get at the instrument, had to remove 111 screws that were designed to never need to be removed, had to deal with baulky tools, and had to go into the sensitive electronics of an instrument and replace the computer cards that send electricity to the instrument.

I watched parts of the spacewalk on NASA TV, and the astronauts were clearly frustrated and stressed. Yet they didn't lose their temper, and they didn't say any foul language (I think the worst I heard was something like, "This is so screwed up." I shocked at how mild that was compared to what I would have said, and I pride myself in keeping my language clean!)

The spacewalk ran hours over, one major job of installing new insulation didn't get done, and some of today's work was done yesterday. But the work they did was something that was never intended to be done to the Hubble, and it worked. The camera turned on after the repair, and quick checkouts said everything was alive.

During later checkout of the instrument, the spectrograph shut down due to a low temperature reading. I think there's a good chance that everything will work out okay once the spectrograph warms up. Just amazing work by the entire shuttle crew!

The STIS is an optical spectrograph; it splits light up into its component colors, which allows for detailed chemical analysis of stars and galaxies. STIS suffered an electronics failure in 2004, and has been sitting idle ever since. When it was working, STIS took the first spectra of planets around other stars, detected black holes in the centers of dozens of galaxies, and allowed all sorts of detailed work on lots of astronomical objects.

Many of my colleagues will be very happy to have STIS working again. Although spectroscopy doesn't produce very pretty pictures, it often reveals much more information than our pictures can. Because of that, spectrographs are often the unsung heroes of telescopes. Both COS and STIS will be used just as much as the new and refurbished imaging cameras on Hubble, but you won't see nearly as many pictures in press releases about these discoveries.

Tomorrow will probably be the Hubble mission's last spacewalk. Astronauts Grunsfeld and Feustel will replace Hubble's other battery pack, replace one of the fine guidance sensors, and then will do as much insulation repair as time allows.

Hubble repairs keep on coming

In the last two days, the astronauts on the shuttle Atlantis have continued to make successful repairs to the Hubble Space Telescope. They've added a new spectrograph (more below), replaced all six of the Hubble's gyroscopes, replaced one of the two battery packs, and opened a camera that was never meant to be opened in space and replaced four circuit boards (more on this also below). The astronauts have had their share of difficulties, including stuck bolts and a new set of gyroscopes that just didn't fit (meaning that the new ones are coming back to Earth, and some refurbished gyroscopes were put in instead).

If you remember, several years ago NASA's then-Administrator Sean O'Keefe announced that, instead of a shuttle mission to repair Hubble, NASA was going to try a robot mission instead. As Julianne at Cosmic Variance noted, it's unclear that the robot would have been able to deal with the bolt and the gyroscopes (never mind replacing circuit boards). I agree that it is hard to imagine how a robot could have accomplished these tasks. Any future repairable telescopes may well be designed for robot repair, but Hubble wasn't.

Anyway, on to the exciting repairs (the batteries and gyroscopes were the most crucial, but aren't too exciting scientifically). First, the new spectrograph, which is called the Cosmic Origins Spectrograph, or COS. COS is a spectrograph (meaning it splits the light up in to component colors) that looks at ultraviolet light. One of the main science questions that COS is going to address is how much and what kinds of matter are located in between galaxies. COS will use quasars as light bulbs, and the matter in between galaxies will absorb some of the light. By careful analysis of the wavelengths of absorbed light and the amount of the absorption, astronomers can figure out where the absorbing light is, how much matter is there, and what the relative amounts of different atoms (hydrogen versus helium versus carbon, etc.) are.

But COS can do much more. For example, collaborators of mine have an approved program to take spectra of white dwarfs in the ultraviolet. So I suspect that COS will be used to study everything from the closest stars in the galaxy to the most distant galaxies, as long as they emit ultraviolet light.

The other major repair was to the Advanced Camera for Surveys, or ACS. ACS is the camera that died due to an electronics failure in January 2007, just hours after we astronomers had submitted many proposed projects to use the camera. ACS has taken many fabulous pictures, including one of the first direct pictures of a planet around another star.

ACS has three cameras: an optical imaging camera, an optical high-resolution camera, and an ultraviolet imaging camera. After the electronics problem, NASA was able to revive the ultraviolet camera using spare electronics, but not the other two cameras. Yesterday, astronauts John Grunsfeld and Drew Feustel removed more than 30 screws using a special tool (gotta keep those screws from floating away!) built just for this spacewalk. Grunsfeld removed four circuit boards from the inside of the camera and replaced them with new ones, then closed the camera back up.

Testing indicates that the repair was mostly successful. As of an hour ago, the ultraviolet camera was working (as it had been, but since all the electronics had been replaced, there was a chance it may not have worked). The wide-field camera, the main optical camera, also is working again. Unfortunately, the high-resolution camera is not working. Space Telescope engineers will keep working to try and figure out if the camera can be revived. It may be that the electronics in the camera were fried two years ago, in which case there is no saving that camera, or it may be that, with a little coaxing, the camera can be revived. But the apparent revival of the wide-field camera is very, very good news. That was Hubble's main imaging camera; and the teaming of ACS with the new WF3 will allow for some amazing images in the future. Still, let's not get too excited yet -- we won't know exactly what condition the ACS is in until it takes some new pictures. Space is hard on electronics.

Right now, the two Mikes (Mike Good and Mike Massimino) are trying to repair another broken spectrograph, the Space Telescope Imaging Spectrograph (STIS). The STIS repair will require removing 111 tiny screws that were never designed to be removed, and replacing more circuit boards. (I have enough trouble with replacing circuit boards in my home computer on Earth; I can't imagine doing it in zero-G with bulky gloves on. However, I often have my cats trying to "help" me, and I assume the astronauts will not have their pets batting around the 111 screws or pawing at the wiring.)

Friday, May 15, 2009

Hubble's Wide Field Camera is Dead; Long Live the Wide Field Camera!

Yesterday, in the first space walk of the Hubble Servicing Mission 4, astronauts John Grunsfeld and Andrew Feustel replaced Hubble's Wide Field and Planetary Camera 2 (WFPC2) with the Wide Field Camera 3 (WFC3), thus aiding in the succession of a nearly royal line of cameras. These cameras are some of Hubble's workhorse instruments, and are responsible for many of the pretty pictures you've seen over the past 19 years.

The first Wide Field Planetary Camera went up with Hubble 19 years ago. It's reign was not all that glorious, due to Hubble's mis-shapen mirror. It was replaced in during the first servicing mission in December 1993 with WFPC2, which has special optics to correct Hubble's blurred vision. The difference is shown in the picture of the galaxy Messier 100 below. The image on the left is from WFPC 1, and is roughly as good as ground-based telescopes can do. The picture on the right is from WFPC2, right after installation.

Messier 100 from Hubble
Image Credit: NASA / STSci / JPL

If the cameras are royalty, WFPC2 is Queen Victoria and Queen Elizabeth II rolled into 1. It has worked admirably for over 15 years, taking over 135,000 images. WFPC2 was all but retired in 2002, when the Advanced Camera for Surveys (ACS) was installed. But, in January 2007 (just a few hours after I put in a proposal to use the ACS), the ACS suffered an electronics failure, and its optical camera was shut down. WFPC2 stepped up to the plate, taking much of Hubble's workload that had been destined for ACS (including my own images). WFPC2 images often can be recognized by their Stealth Bomber shape; this shape was due to the optics needed to correct Hubble's vision and the desire to put in a very high resolution detector in one corner of the camera. An example of this unique shape is the famous Hubble Deep Field image.

WFPC2 has been showing signs of age. It is not as sensitive as it used to be due to radiation damage, and certain parts of the image -- if I live as long relative to my life expectancy as WFPC2 has, I'll live close to 240 years. It's deserving of its retirement, and will be on display in the Smithsonian Air & Space Museum this fall.

WFPC2's replacement is WFC3. The "P", standing for "Planetary", was that high-resolution detector in WFPC2. It was designed for taking pictures of planets, but has been used for lots of high-res imaging. The entire WFC3 camera has the same resolution as the planetary camera, so it was decided not to include the "P" in the name. This seems silly to me, as a large fraction of astronomers, myself included, often wrongly refer to the new camera as WFPC3. Whatever.

WFC3 will really shine in the near infrared, or wavelengths of light just beyond what the eye can see. Currently, a camera on Hubble called NICMOS takes those images, but WFC3's sensitivity far outpaces that of NICMOS. An ever-increasing amount of astronomy is done in the near-infrared regime, so WFC3 will be used a lot in this mode.

In a few days, the shuttle astronauts will try and repair the ACS camera. This is a tough repair, because it involves replacing a circuit board. If the repair is successful, ACS will probably keep taking most of the optical images from Hubble, because it has a slightly bigger field than WFC3 and it is more sensitive in the optical. But if the repair doesn't work, WFC3 is more than capable of filling the void. Either way, WFC3 is new, and could operate for a decade or more! Early tests yesterday show that WFC3 is alive; we'll have to wait for the first pictures after the shuttle leaves to see just how good this camera is. I suspect it will be fantastic. Welcome to the Hubble family, WFC3!

In other repair news, the astronauts replaced the science data formatter that failed last fall, leading to the 9-month delay in this mission. The replacement also appears to be alive and ready to work!

As I type this, astronauts Mike Good and Mike Massimo (who you can follow on Twitter) are on the second spacewalk, replacing all of Hubble's six gyroscopes. Hubble needs at least two to point, and NASA prefers to use three. Hubble was down to two gyroscopes, so the fresh set was desperately needed and should keep Hubble going for a long time to come. They will also replace one of Hubble's two batteries. These batteries are as old as Hubble itself (imaging your car battery lasting 19 years!), and were threatening to fail. Again, the new batteries could keep Hubble going for another two decades, if time is good to the rest of the telescope!

For a well-written story on the life of WFPC2, check out this JPL press release.

Thursday, May 14, 2009

Herschel and Planck launch

With all eyes on the shuttle's final servicing mission to the Hubble Space Telescope, many of you probably have not heard of today's other giant space news: the launch of the European space telescopes Herschel and Planck. The single Ariane 5 rocket containing both satellites launched successfully at 9:12am EDT this morning, and the latest news is that both satellites successfully separated from the rocket and are on their way.

Planck is the latest satellite to study the Cosmic Microwave Background, the "echo" of the Big Bang discovered by Bell Labs engineers Penzias and Wilson back in the early 1960s. While NASA's COBE and WMAP missions have learned a lot about the early Universe from studying the Cosmic Microwave Background in detail, there is still a lot more information encoded in the light from this echo. Planck has two big advantages over the previous missions. It has sharper vision (high angular resolution), allowing Planck to study the smallest structures in the early Universe. This will allow for some of the first strong tests of hypotheses like inflation, the idea that in the first instants of the Big Bang, the Universe expanded at a rate much faster than the speed of light (space can do this). Many of the ideas behind inflation are similar to many of the ideas behind Dark Energy, so it is possible that Planck will be able to shed light on Dark Energy, as well.

Planck also can measure the polarization of light from the Cosmic Microwave Background. If you think of light as a wave travelling through space, polarization is the direction in which the wave is "waving." Imagine standing on the beach and watching the waves come in. The waves are moving toward the beach, but if you are out in the ocean, you will bob up and down as the waves pass. So, the polarization of ocean waves is up and down (more or less).

Light waves can have polarization, too. They can be polarized up and down, left and right, and even as a circle (meaning the wave sort of corkscrews through space).

Light from a star comes out as unpolarized, on average. But if the light reflects off of something, it tends to become polarized. This helps explain why polarized sunglasses work -- the sunglasses only let through light polarized in directions different from the polarization of reflected light, so sunlight glare from reflections gets filtered out by the sunglasses.

For hundreds of thousands of years after the cosmic microwave background light was created, it travelled freely through the Universe. The Universe was filled with neutral hydrogen and helium atoms, and light can pass right by neutral hydrogen or helium without interacting. (Don't believe me? Let the helium out of a helium-filled balloon. You won't see the helium, because light passes right through it without interacting.)

When the first stars formed in the Universe, they were very hot. The light from these stars was sufficient to ionize the hydrogen and helium, in other words, the starlight was able to strip electrons away from their parent atoms. Light and electrons interact very strongly; light tends to bounce off of electrons. (This is kinda why metal is used in mirrors; the electrons in many metals are more or less free to roam around, and light bounces off of them.) Bouncing light = reflecting light = polarized light!

So, since Planck can detect polarized light, it can determine when the light in the Cosmic Microwave Background started to become polarized. This tells us when the first stars formed in our Universe, which is still unknown.

Herschel, the other telescope launched today, is an infrared telescope. It can look at light that has wavelengths of 55 to 672 micrometers (or about 0.05 to 0.67 millimeters). Optical light has wavelengths of a fraction of a micrometer, and radio waves have wavelengths of millimeters to many meters long.

This regime of light is hard to study. Everything around us emits infrared light, including us and the air around us. The hotter something is, the more light it emits. Therefore, to study the Universe in this infrared light, our telescope needs to be outside of Earth's atmosphere and cooled to temperatures near absolute zero. The Herschel Telescope uses liquid helium to cool its instruments to 0.3 Kelvin, or a third of a degree above absolute zero, the coldest possible temperature.

There's another trick to looking at infrared light in this wavelength range. As you may remember, light can be thought of as either a particle (a photon) or a wave. Our current technology makes it easy to detect photons at short wavelengths (your digital camera detects individual photons), and easy to detect waves at long wavelengths (radio antennas work by detecting waves).

At wavelengths of around a few hundred microns, it is hard to detect photons and hard to analyze waves. So, infrared telescopes working in this range have a technological challenge, no matter whether they decide to detect waves or photons. Herschel is going for the wave detection, and the technology required to analyze these waves has proven quite challenging to develop. But the engineers did it!

Herschel's science is designed around looking for cold things. This includes dust and gas clouds in deep space, and the cold outer regions of forming stars, where planets might be forming. Herschel can also study some of the very first galaxies in our Universe, galaxies so far away that normal infrared light has been stretched by the expansion of the Universe into this far infrared. We have learned a lot about nearby galaxies in infrared light from telescopes like the Spitzer Space Telescope (Hubble's infrared cousin); Herschel will allow us to compare galaxies in the early universe to the nearby galaxies that we think we understand.

Congratulations to the Planck and Herschel teams on a successful launch!

Tuesday, May 12, 2009

Chasing down Hubble

After yesterday's safe launch of the Space Shuttle Atlantis, the orbiter is spending today and part of tomorrow chasing down Hubble.

I used to wonder why the shuttle always takes a few days to track down the Hubble, the International Space Station, or other satellites. There's no physics reason why we couldn't launch a rocket directly from Florida to rendezvous with Hubble or the space station just a half hour later. Instead, the shuttle tends to launch into a lower orbit, and then uses its Orbital Maneuvering System (the little engines on the pods near the shuttle's tail) to transfer to the proper orbit over the next couple of days.

There are many reasons for this. The most obvious one is safety. If you directly launch into the orbit of the space station or Hubble, and you are slightly off course, you run the risk of smashing the two things together at several hundred kilometers per hour. That would be bad. Or the orbiter could be on course, but there could be debris (say a piece of insulation has come off of Hubble but wasn't detected by the ground for some reason) near the Hubble that the shuttle would then slam into, with disastrous results. By transferring from a lower orbit, the shuttle can close in at relative speeds of a few miles per hour, plenty slow enough to make course corrections and to look out for any unexpected debris.

The Hubble telescope also orbits in a pretty high orbit for the space shuttle, at an altitude of about 565 km (about 350 miles), while the space station orbits at an altitude of about 350 km (220 miles). At the altitude of the space station, the outer reaches of Earth's atmosphere are thick enough to cause a satellite to fall back to Earth in a few years (so the space station is constantly boosted by visiting shuttles and Russian Soyuz capsules; click here to see the height of the space station over time). The Hubble has no engines, so it was put into the higher orbit. At its orbit, satellites can last 20 or more years. (The exact length of time depends on the mass and shape of the satellite and on the details of Earth's atmosphere, which can change dramatically depending on the sun's activity.) Since the Hubble is in a high orbit, it takes more fuel to get there, and more fuel to get back down to Earth.

By launching into a very low initial orbit, the shuttle can be checked out by the astronauts and Mission Control to make sure every system is working before it moves to a higher orbit. Suppose that there is a fuel leak. In a low orbit, the shuttle can re-enter and try to land with very little fuel. If the shuttle went straight to a high orbit, there could not be enough fuel to get the crew back. Or if, God forbid, the orbital engines fail altogether, in the low initial orbit the shuttle will fall back to Earth in a matter of days, and the astronauts will have enough air, food and water to last until the shuttle naturally re-enters, giving the astronauts a chance to survive this failure. (I don't know how much this scenario figures into the choice of an initial orbit, though I do know that, if the orbital maneuvering engines don't work at all, the shuttle won't reach a final orbit, and it can make a single trip around the Earth and land back in Florida.)

And, lastly, waiting to reach the space station or Hubble gives the astronauts a couple of days to prepare for the approach and docking. After the stress of liftoff, a few days are probably helpful to unwind before the stress of the Hubble repairs.

There are many other minor reasons, both technical and practical, for taking time to approach your target. Mainly, I wanted to point out that this is a deliberate choice. If there were some great need, a rocket COULD launch more or less directly to the proper orbit. (The shuttle does have some technical limitations in this regard, but even it could reach a final orbit in just a few hours instead of a few days). But, primarily, it would be highly dangerous to do so. Even if we learn that Atlantis's heat shield has been compromised and we need to launch a rescue mission, that rendezvous is scheduled to take several days, as both shuttles would have plenty of air, food, and water, so there'd be no need to risk a rapid rendezvous.

As a reminder, you can follow the progress of the Hubble repair mission here on NASA's STS-125 webpage. You can also track Hubble's location on this webpage; once the shuttle reaches Hubble, you'll know where they all are!

Friday, May 08, 2009

Hubble, Here We Come

STS 125 Crew
Image Credit: NASA
If all goes on time, the space shuttle Atlantis will launch Monday at 2pm EDT on NASA's fifth and final mission to repair the Hubble Space Telescope. In the primary sign that this is a government operation, the mission is known as "Servicing Mission 4", because Servicing Mission 3 was split into two separate visits, 3A and 3B. Whatever.

Anyway, you can follow the mission many ways. In addition to traditional media, you can watch the launch and the spacewalks on NASA TV, available either from your cable/satellite provider or available streaming over the web. The mission has a page on Facebook, on MySpace, and a blog hosted by NASA. You can also follow the mission on Twitter, both through Hubble's Public Affairs Office and through the experiences of astronaut Mike Massimino, one of the mission specialists. NASA's webpage for Servicing Mission 4 contains news on the mission, as well as lots of other mission-related media and activities. And I'll do my best to keep you up to date.

Hubble itself has been trundling along for the past several months. It's not in great shape; only a couple of cameras are working, the batteries are old, and it has to send data down via a spare part. But it still has been taking some extraordinary data despite the numerous delays in the repair mission. As I mentioned last fall, these delays actually turned out to be a good thing, allowing the mission directors and astronauts to find a way to replace the broken data recorder without having to bump any other critical repairs.

During this mission, astronauts will, among other things, replace the old rechargeable batteries with new ones, replace all of Hubble's gyroscopes, fix a guidance sensor, repair some torn insulation, and install a latch so that a future rocket can grab onto Hubble and de-orbit the telescope in a controlled manner, once Hubble's life is over. The astronauts will also give Hubble two new cameras. One, the Cosmic Origins Spectrograph, will look at ultraviolet light; the other, called WFC3, is the third in a series of cameras that can take pictures in optical and infrared light. The astronauts will also attempt to repair two broken cameras, one called STIS that takes spectra of stars, and one called ACS that takes regular pictures. Both of these cameras died due to circuitry malfunctions (ACS died less than a day after we had all submitted proposals to use it during 2007!) Unlike the telescope as a whole, these cameras were not designed to be repaired, and so there are some very clever tools and techniques that had to be invented to allow the astronauts to repair the instruments.

All in all, this is a very complicated mission, and not without many risks. The astronauts are risking their lives to repair Hubble; something we astronomers are deeply grateful for and a debt we cannot repay. The repairs are all complicated. Some of them we can live without, such as if one of the cameras cannot be installed for some reason. But other repairs, such as the batteries or gyroscopes, are crucial to the well-being of the telescope. If those repairs fail, Hubble is a goner. We know that the repair team, both on the ground and in space, will do their absolute best to repair Hubble; if something doesn't work, it will not be due to a lack of training or will on the part of the repair team.

If successful, the repairs will allow Hubble to work on another several years, perhaps as many as 10 or 15 (if we get really lucky). That is fantastic for a telescope that was almost a failure due to a malformed mirror. Counting this mission and the initial launch of Hubble, our astronaut corps will have admirably serviced Hubble six times, and the data we've gotten has been worth every penny.

Tuesday, May 05, 2009

Happy 70th Birthday McDonald Observatory

McDonald Observatory Telescopes
Image Credit: The University of Texas McDonald Observatory
Today is the seventieth anniversary of the dedication of the first telescope at the McDonald Observatory. Here is a memorandum on the occasion from the current Director of the Observatory, Prof. David Lambert (links added by me):

MEMORANDUM May 5, 2009

TO: Everyone

FROM: David L. Lambert

SUBJECT: McDonald Observatory's Seventieth Birthday!

Today is the seventieth birthday of the McDonald Observatory. On Friday, May 5, 1939, the 82-inch telescope was dedicated (13 years after W.J. McDonald's death on February 6, 1926).

Recently, I have been rereading parts of David Evans and Derral Mulholland's book "Big and Bright". I thought it would be fun on this birthday to recall the birth of the McDonald Observatory.

Finally, it was Friday, 5 May 1939; the long-awaited day had arrived. The participants were transported by bus to the observatory, where the ceremonies were to be held on the observing floor of the telescope dome. There, they found Elvey at the mechanical controls of the telescope and observing stations, Seyfert running the projector, and Kuiper serving as scientific aide to the press.

Henry Norris Russell presided over the morning session, which Harlow Shapley opened with "Recent Advances in Astronomy." He was followed by J. Gallo of the National Observatory of Mexico, who described astronomical work in his country. The morning wound up with a description of the telescope by J. S. Plaskett. Telescope domes are not renowned for their acoustics. Plaskett, speaking on the technicalities of mirror testing from the top of the coudé spectrograph housing, was alternately inaudible and incomprehensible.

For the official participants, lunch break was a full-blown chuck-wagon barbecue dinner and rodeo at the Prude Ranch, compliments of the Warner and Swasey Company. Earlier, company treasurer John C. Kline had remarked on the cost, but had added that "Charles Prude understood that [Charles Stilwell] wanted a real show, and . . . we will get one." The astronomers were treated to several regular rodeo events, such as cattle roping, bronco riding, and calf bulldogging in an arena improvised from a row of parked automobiles. There was also a parade of "old-timers" and a Mexican band.

The formal dedication ceremonies resumed at 3:00 P.M., along with the arrival of bad weather. Most observational astronomers are inured to such perversities of natural phenomena. Nonetheless, one participant wrote home with the comment that "it is said to rain here only five days out of the year, and we have already had 60% of this year's quota in the past week."

The final speaker at the afternoon's dedication ceremony was University of Texas President-elect Homer P. Rainey, who declared that:

"We are here to dedicate the Observatory to the most ancient and purest of all the sciences. [May it] stand as a symbol of the freedom of man's mind to explore the boundless areas of truth without any restrictions whatever. To these ideals, I dedicate the McDonald Observatory in the name of the University of Texas, and I now declare it open for research."

As David Evans and Derral Mulholland remarked:

This last was a mild bit of hyperbole, however excusable. The McDonald Observatory had been open for research for most of five years, and even the McDonald telescope had been in use for two months.

Letters and telegrams were sent to wish the McDonald Observatory well. In this the International Year of Astronomy, I take, as my final extract from "Big and Bright," this delightful piece:

A unique communication came from the astronomers at Florence, Italy. It is a highly decorated colored scroll inscribed in Latin. Translated, its message reads:

From the hills sacred to the memory of Galileo, who was the first man to scrutinize the stars with a small telescope, the astronomers of Arcetri join in greeting at its inception a New World observatory that will reveal the paths of the universe.

Dated at Florence five days after the kalends of May 1939, the 17th year of the restored Fascist era

Strictly speaking, that date would have meant the sixth of May, but maybe the Florentines were a little hazy about the exact date of the dedication. The document was signed by several distinguished Italian astronomers, among them Giorgio Abetti, Atilio Colacevich, Guglielmo Righini, and Mario Fracastoro.

Their scroll can be found in the Peridier Library. (see photograph below)

On this, the 70th birthday of our Observatory, let's drink a toast to Astronomy at UT Austin, the W.J. McDonald Observatory, the Department of Astronomy, and colleagues and friends past and present.

Monday, May 04, 2009

Binocular vision

Most every holiday season, I blog about how to choose a first telescope for you or someone else, and I recommend considering binoculars. Today's 365 Days of Astronomy podcast by Robin Scagell discusses stargazing with binoculars, and it outlines the advantages and limitations of binoculars for astronomy.

There's one major advantage of binoculars that the podcast leaves out, though. Binoculars are good for many uses other than astronomy, so if you find that astronomy observing isn't your cup of tea, and/or if you do a lot of other outdoor activities such as hiking, sightseeing, or birdwatching, binoculars will prove quite useful and portable. Telescopes are less portable and harder to use for non-astronomy purposes.

While we are on 2009 International Year of Astronomy topics (the 365 Days of Astronomy podcast is produced as part of the IYA), why not vote in my latest opinion poll on how you have been celebrating the International Year of Astronomy? Voting ends today.