Around and around and around it goes...

This morning, at 7:42am EDT, the Hubble Space Telescope reached a new milestone by completing it's one hundred thousandth (100,000) orbit around the Earth.

The Hubble orbits the Earth in what is known as a "low-Earth orbit," or "only" 600 kilometers (375 miles) above Earth's surface. While this sounds very high, it's not, in space terms. The space station and space shuttle also orbit this low. In low-Earth orbit, it takes a satellite about 90 minutes to orbit the Earth. But at these altitudes, the Earth's atmosphere is still present (although very, very tenuous), and if you don't put a booster rocket on your spacecraft, it will fall back to Earth in just a few years or decades.

In order to stay in orbit, the Hubble has to move at a speed of about 7.5 kilometers per second, or almost 17,000 miles per hour. When the space shuttle goes to repair Hubble, it is also moving this fast. How can the astronauts safely catch the Hubble? It's all relative speed. Although both spaceships are moving at 17,000 miles per hour, compared to one another, they are moving only a few miles per hour (more when the shuttle is moving in to catch it, and much less when the shuttle sticks out its arm to grab Hubble). It's like passing a car going slightly slower than you on the road. Although you are both moving at 65 miles per hour, you can take several minutes to pass each other. Plenty of time to see what their kids are watching on the DVD, get a good look at the driver, and perhaps even try to pass some Grey Poupon.

In the 18 1/3 years it took Hubble to go around the Earth 100,000 times, it covered a distance of 2.7 billion miles. That sounds like a lot, especially if you are moving at 17,000 miles per hour! But, in space, 2.7 billion miles is only about the distance from the Earth to Neptune, and only 1/10000th the distance to the nearest star. We have four space probes (Pioneer 10 and 11, and Voyagers 1 and 2) that have travelled much further. And many other satellites around the Earth have been longer-lived, and have logged many more miles than Hubble.

Basically, Hubble hasn't set any records. It's just reached a nice, round number that is kinda fun to celebrate. So, in that line of celebration, NASA has released some colorful new pictures of a star-forming region in the Large Magellanic Cloud (LMC), one of the Milky Way's own satellite galaxies. And the LMC has only completed one or two orbits around the Milky Way in the 13 billion years its been around. So, our Hubble has an entire galaxy beat! (Of course, instead of an altitude of 600 kilometers, the LMC is at a distance of about 160,000 light-years, and it is travelling about 40 times faster than Hubble).

Also, NASA has a contest where you can win a nice print of a picture from the Hubble; look on the Hubble's home page for that contest (which ends after this week).

Happy Birthday Hubble!

18 years ago today, the Hubble Space Telescope was launched on the space shuttle Discovery. It's hard to believe the telescope is now old enough to vote (I don't know who the Hubble would support in the presidential election; probably either McCain, Clinton, or Obama). Hubble was originally designed for a 15 year mission, so it has exceeded our hopes and desires. And, with a refurbishing mission on the way later this year, HST should be good for at least another 5-10 years.

In honor of Hubble's birthday, NASA has released a collection of pictures of 59 colliding galaxies. There's lots of neat things in those pictures -- dust and debris being flung every which way from the collision, bursts of star formation, giant black holes flaring to life, and more.

Thanks to all at NASA for their hard work with Hubble, and thank you to all you taxpayers for you money that keeps the telescope running!

Proposing to use Hubble

Today, optical and ultraviolet astronomers around the world are scrambling to finish proposals for the Hubble Space Telescope. Tonight, at 8pm Eastern Time, proposals are due for the Hubble's 17th Cycle (each cycle is roughly a year) of operation.

This time around, there are two new instruments that astronomers hope to use, if the Space Shuttle's servicing mission works as planned. One is a spectrograph for analyzing ultraviolet light, that high-energy light that can be harmful to humans, but which contains a wealth of information about stars and distant galaxies. This spectrograph is called the "Cosmic Origins Spectrograph," because it will be useful for interpreting light from the earliest galaxies. More to the point, the light that we detect on Earth from the earliest galaxies is ultraviolet light that the expansion of the Universe has stretched into visible and optical light. So the Hubble's spectrograph will be used to explore more nearby galaxies (where we think we understand what is going on), and that information used to interpret the light from more distant galaxies.

Another new instrument will be a new imaging camera, more sensitive than the current one on Hubble. Like other cameras, this one will be able to take pictures in ultraviolet and visible light for studies of just about anything.

So, although these cameras are still on Earth, waiting to be launched by the space shuttle, we are starting preparations to use the cameras. It takes months for people to sort through the hundreds of proposed projects, select the very best ones (and some back-up plans in case one of the instruments fails or repairs don't work), and plan out an observing schedule. By the time that is done, we hope that the space shuttle will have safely traveled to Hubble and gotten back in tip-top shape.

Still, it is a little nerve-wracking to write proposals for broken cameras that we hope to fix, but may not get fixed, or for cameras that are not yet there and may not function exactly as advertised. And, since each proposal takes a lot of time if you want to do it properly, we hope that we are not wasting that time.

Welcome home Atlantis!

Image Credit: NASA / Bill Ingalls

Yesterday morning, the space shuttle Atlantis landed after a 13-day mission to the International Space Station. The mission added a new science laboratory to the Space Station, and, more importantly, took the crew safely to space and back.

Atlantis's next flight will be the next and final repair mission for the Hubble Space Telescope. The fifth servicing mission (called "Servicing Mission 4", because Servicing Mission 3 was split into two missions, and because, well, sometimes people just can't bring themselves to make sense) will fix up Hubble and allow it to live another 5 years or more. Hubble will get new batteries, new gyroscopes, new cameras, new pointing systems, and some other general repair work. Astronauts will also attach a docking port that will allow a future rocket to attach to the telescope to bring it down safely when its useful life is over.

The trip may also mark Atlantis's last trip into space. Right now no future flights are scheduled for this shuttle, and it may be used for parts to keep Discovery and Endeavor flying until the shuttles are retired in 2010. But all of that can change.

Most of us in the astronomical community are sitting on pins and needles, hoping that the mission is a success and is safe. And, in the meantime, we cross our fingers for every shuttle launch, hoping for safe travels for our astronaut friends!

CSI: Universe --- Who set off that explosion?

Image credit: Jon Morse (University of Colorado) and NASA

In 2004, astronomers reported a possible supernova (the explosion of a dying star) in the galaxy UGC 4904, a barred spiral galaxy about 75 million light-years away. However, the apparent explosion was awfully faint for a supernova, and it faded away too quickly for a supernova. And so, the "transient" (as such events are called) was forgotten.

On the night of October 9, 2006, amateur astronomers in Japan detected another transient in the same galaxy, a transient that was confirmed as a supernova several nights later. Not only that, but the supernova seemed to be coming from the same part of the galaxy as the first transient. What was going on? And just recently, European astronomers were able to do a careful alignment of the images of both events, which confirms that they are coming from the same spot. What's going on?

Very massive stars, those nearly 100 times the mass of the sun, live short and violent lives. These stars live their lives on the brink between gravity holding the star together and the radiation from the nuclear reactions at the star's center ripping the star apart. Sometimes these very massive stars become unstable, and can rapidly lose large amounts of material, many times our sun's mass. As that material flies off in a massive eruption, the star can get significantly brighter -- just like the first transient in UGC 4904. Typically, these stars seem to settle back down after the eruption, just like a little burp can make you feel better after you've eaten too much. And we think (or thought) that these stars would go on to live for another 200,000 years or more.

But the supernova throws that into question. Did the same star that erupted a few years ago then go supernova, meaning it had used up all of its nuclear fuel much faster than astronomers thought?

Maybe, maybe not. Massive stars tend to be born in clusters of stars, with many other very massive stars around. And many of these massive stars have companion stars in tight orbits. Because we don't have pictures of this galaxy taken with the Hubble Telescope, we can't see individual stars in this galaxy, so we can't know if the eruption of the star in 2004 and the explosion of a star in 2006 came from the same star. Based on the coincidence and the close timing, it would make sense that they are related. But maybe this just was two separate stars, and the timing was a coincidence.

If eruptions of material from massive stars often results in a supernova shortly thereafter, we should see this occurrence more often. It's only been in the last decade that astronomers have been diligently searching nearby galaxies for supernovae, so more time is needed before the book can be closed on this case.

But maybe we don't have to look too far away. In the southern hemisphere, the star Eta Carina is a massive star, 120 times the mass of the sun. In 1843, the star temporarily became the brightest star in our sky after the sun, despite being 8000 light-years away. Then the star rapidly became fainter than the human eye can see, and it has slowly gotten a little brighter since. This is thought to be the same type of eruption that was seen in UGC 4904 in 2004. The picture above shows a Hubble Space Telescope picture of Eta Carina -- the star is buried in the middle of two giant, expanding bubbles of material. Those bubbles were probably created in the eruption 160 years ago. So, will Eta Carina go supernova soon? 160 years seems a lot longer than 2 years, but in astronomical terms, they are both almost instantaneous. But maybe we will have to wait 200,000 years to see Eta Carina explode. If Eta Carina were to explode in the next several decades, then we would have to re-think these massive eruptions.

Hubble, here we come!

Tonight, if all goes well, the space shuttle Atlantis will launch on a visit to the International Space Station. Since the last shuttle launch, NASA's suffered through a series of bizarre events, including a tabloid-worthy love triangle, a hail storm resulting in an ugly-looking fuel tank, and a train carrying booster parts that derailed twice on its way across the country. With a successful and safe mission, hopefully NASA can put these odd events behind it.

In even better news (in my humble opinion), NASA also announced a launch date of September 10, 2008, for the next and final Hubble Telescope repair mission. Servicing Mission 4 (which is actually the fifth repair mission -- typical government counting, since Servicing Mission 3 was actually two visits) will install two new cameras, repair one existing camera (hopefully), replace the rechargeable batteries, replace broken gyroscopes, add new pointing sensors, and repair some insulation and other minor damage.

Personally, I question the usefulness of the International Space Station. It's horrendously expensive, and hasn't been able to do the promised science because of budget cutbacks. But we've agreed to build it, and we might as well use it (if we can find useful things to do). And, each passing shuttle launch brings us closer to both the Hubble repair and the end of the space shuttle program.

So, if you haven't watched a shuttle launch in a while, why not take some time to watch? Launch is scheduled for 7:38pm EDT. If you don't have access to cable TV, you can always watch NASA TV online. The launch has to happen in a 10 minute time frame for the shuttle to be able to meet the space station; otherwise, they'll have to try again another day.

Will Astronauts visit Hubble's replacement?

If next fall's visit by astronauts is successful, the Hubble Space Telescope will be with us for at least another five years. But plans are already in place to launch NASA's next large space telescope, the James Webb Space Telescope, in 2013 (although I'd be surprised to see it launched that year).

Although the Hubble has been well-served by four (and soon a fifth) servicing missions by astronauts, we've always assumed that JWST would not be able to be visited by astronauts. Hubble is in low Earth orbit (just a few hundred miles up), where the Space Shuttle can easily fly. But the JWST is going to be at the second Lagrange point, a spot about 1 million miles away from the Earth where the Earth and the Sun's gravity balance perfectly. The main reason for this distance is to get the telescope, which will look at infrared light, far from the heat of Earth. But none of our current rockets can carry humans to this Lagrange point, so it seems that repair of the telescope is out.

So I was surprised today when NASA announced that it was going to add a docking port to JWST in case future astronauts ever visit the spacecraft. Their reasoning is that if this expensive telescope fails to work, their new Orion rockets might be able to take astronauts to the Lagrange point to try and salvage the telescope.

If astronauts were to go to the JWST, it would mark the furthest humans had ever ventured away from the Earth -- it is nearly four times further from the Earth than the moon. It would also be a very risky and very expensive mission. Would it be worth the trouble? I don't know. Certainly astronauts would probably like to try if the chance of success seemed reasonable, and I don't doubt their ability to fix the spacecraft.

But adding a docking ring adds weight and complexity to the telescope, two things that are not always desirable. I am not a space engineer, so I really do not know how much the docking ring affects the spacecraft. But it could also mean that some science may need to be scaled back to reduce the weight of the telescope. Again, this is just my guess, I don't know.

So, I have mixed feelings about the announcement. In some ways, I am glad NASA is thinking ahead and allowing for new possibilities we hadn't previously dreamed of. But I have reservations, and until I know more about the plans, I'll remain skeptical.

Looking through Hubble

Friday was a day that many observational astronomers dread. It was the day that the time allocations on the Hubble Space Telescope were announced. Some of you may remember my writing about this proposal back in January. I submitted a proposal, and 12 hours later, Hubble's camera that I had asked to use quit working. Because so much of the time astronomers asked for used this camera, and because the deadline had just passed, NASA extended the deadline for a couple of weeks.

Two weeks ago, while I was learning about exploding white dwarfs, dozens of astronomers met in Washington, DC to choose which of the proposals would get time on the Hubble telescope. It was a tough job, as astronomers asked for over five times more time than was available. And this was after some large programs were knocked out because they required the now-defunct camera!

When so much time is requested, it is inevitable that perfectly good requests are denied. So, I felt absolutely ecstatic when I learned that I was granted Hubble time. For the first time ever. And I was worried that I was asking for a lot of time, which can hurt a proposal.

It may be 15 months before my images are taken, and I have to keep my fingers crossed that nothing else breaks before I get my data. On the good side, at the end of the next 15 months, astronauts should be up fixing the Hubble one last time.

Curses! Foiled again.

If you remember from a the few posts ago, I spent much of the past 2 weeks writing proposals to use the Hubble Space Telescope. So, you can imagine the foul mood I was in yesterday when NASA announced that Hubble's main camera quit working Saturday morning, only 11 hours and 26 minutes after the deadline on proposals. And, of course, this is the camera I was proposing to use in my work.

The camera is almost fully dead due to problems with the electronics. It may (or may not) be possible to fix it when astronauts come to repair the Hubble in about 18 months, but they have a long list of things to do already, and the astronauts will be installing a camera that is almost as good as the dead camera in some respects, and better than the dead camera in other respects.

The camera that died, the Advanced Camera for Surveys (ACS), was truly the workhorse instrument of Hubble. At the end of the day on Friday, there were 747 proposals to use the Hubble over the next year; 498 of those were to use ACS.

NASA has decided to re-open the system to proposals in order to try and fill the gap left by the loss of ACS. I might be able to change my proposal to use another, older camera that isn't as powerful as ACS. It has a smaller field of view, and is much less efficient at detecting light. But, given the choice between that and none, I'll take the older camera.

Proposing to use telescopes

Whew! I have worked harder this week than for a long time, all trying to get some different proposals to use the Hubble Space Telescope done. I sent one in a few minutes ago, and other collaborators at other institutions are putting finishing touches on others, so I can finally relax.

Many of you probably are wondering, "What the heck is this proposal he's talking about, anyway?" So let me explain.

The vast majority of professional astronomers do not work in front of a telescope. We spend most of our time in an office in front of a computer to do our work. Professional astronomers share all of our large telescopes with other astronomers at our institutions, at other schools, and around the world. So if I learn of a neat object I want to study, I can't just jump in my car, drive to the mountain top, open up the dome and start looking. Somebody else is probably already using the telescope, and they won't be too happy if I force my way in to the dome and try to take over for the night.

In order to get the telescope, I must start by writing a proposal. A proposal has two jobs. First, I have to show that the science I want to do is interesting. If I say I want to see what phase the moon is, people will say that is boring and stupid, and they won't waste time on my project. But if I say I want to look for new moons around Pluto because any such moons would help to tell us how Pluto formed, then people might start to think it was interesting.

Second, I have to prove that my project is suited to the telescope I am asking to use. If I try to take a picture of Venus with the Keck 10-meter-wide telescope in Hawaii, there will be so much light I will hurt the cameras, which will make a lot of people mad. Likewise, if I say I want to take a detailed look at super faint galaxies with a tiny telescope, I won't get anything useful, because small telescopes can't see really faint things.

So, observatories ask for proposals to use their telescopes one to four times a year. A group will then get together to evaluate the proposals. Is the science worthwhile? Is the telescope the right one for the job? If so, they'll put me in a schedule to use the telescope. If not, then they'll say "sorry, better luck next time," and I won't get to use the telescope.

As you can guess, being able to write a good proposal is an important skill for astronomers. I've spent several days (most of the last week and many partial days over the past month) working on my proposals to use the Hubble Space Telescope. But my proposal only has about 5 pages of text, plus a couple of graphs. They won't take anything longer, or else the committee that assigns time will have to sift through tens of thousands of pages, as there are often more than 1000 proposals to use the Hubble! That's a lot of reading.

For fun, I'm putting a PDF version an old proposal from 2004. The project got time on the Keck Telescope that fall. You can try and read it if you want, though I will warn you it is technical and quite boring. And you will find a few grammatical mistakes, typos, and stylistic problems. It's amazing how much of that can sneak through even though you've been staring at the same 5 pages for days.

And to those who have sent me emails in the last month, I will get around to answering them now that I am both home and finished with deadlines. I'm sorry it is taking so long.