Monday, October 31, 2005

Happy Halloween!

It is a spooky day here at Steward Observatory. So far I have seen a devil prowling the hallways, and the business office has been taken over by the Cirque So Lame (pictures if/when they become available). Even my daughter's guinea pigs Dexter and Cloud have joined in the fun.

Did you know that Halloween, also known as All Hallow's Eve, is an astronomical holiday? Tomorrow, All Saints Day, is a cross-quarter day, or the day halfway between the fall equinox (first day of fall) and the winter solstice (first day of winter). Two of the other three cross-quarter days are still holidays in western culture: Groundhog Day and May Day. The other one (August 1), was known as "Lammas," but Lammas is rarely known outside of religious circles.

Thursday, October 27, 2005

Here's Mars!

Have you noticed a bright orange "star" in the east after dark? It's hard to miss, so go look for it. This "star" is by far the brightest thing in the east. But this is no star, it is the planet Mars. On Saturday, Mars will make it's closest approach to Earth in over two years, and it will be another 13 years until Mars is this close to Earth, "only" 43 million miles away. Here's a Halloween experiment to help you imagine this scale. Start with the pumpkin on your doorstep. That represents the sun. On this scale, the Earth is a pea located about 150 feet away. Mars would be a half pea located another 70 feet away from the Earth.

So why will it be another 15 years until Mars is this close to Earth, if it were this close just two years ago? This online simulator shows the position of the Earth and Mars as both planets orbit the sun. It takes the Earth one year to orbit the sun, and it takes Mars almost 2 years to finish an orbit. So, the Earth passes Mars about every two years.

But Mars's orbit around the sun isn't a perfect circle. At its closest approach to the sun, Mars is 130 million miles (206 million km) away from the sun, and at its furthest, Mars is 156 million miles (249 million km) away. So, sometimes when the Earth passes Mars, Mars is close to the sun, and therefore closer to the Earth. At other times, Mars is further from the sun (and further from the Earth).

Two years ago, the Earth passed Mars just as Mars was at its nearest point to the sun, and Mars was closer to the Earth (only 35 million miles away) than it had been in 50,000 years! This year, Mars is a little further away from the sun, and so further from us. Again, watch the little simulation I linked to above.

So, how would the Earth look from Mars right now? Would it be a bright blue dot in the sky? Would you be able to see continents with a telescope? No. Although the Earth is close to Mars, we almost directly between Mars and the sun. The Earth would be too close to the sun to see safely! And, even if you could look safely at the Earth, you'd be looking at the Earth's night side, and it would be dark!

Would you like a chance to see Mars through a telescope? Over the next few weeks, your local astronomy club will certainly be having some sort of "Mars party." They always welcome newcomers to look through their telescopes at the Red Planet! You can find the astronomy club nearest to you from this Sky & Telescope directory. Don't wait! In a few more weeks, the best views will be gone for 15 years (though we'll get another, less favorable view in two years).

Want to see pictures taken through telescopes in the last few days? Look here!

Wednesday, October 26, 2005

First Light!

The Large Binocular Telescope, a pair of 8.4-meter (27-foot) diameter telescopes being built here in Arizona, has seen first light! The above picture is the first official picture taken by the telescope, and it shows the edge-on galaxy NGC 891, a spiral galaxy viewed from the side. The galaxy is in the constellation Andromeda and about 24 million light-years away. When the light in this picture started its journey, the first elephants had just evolved, and the first early monkeys were evolving.

First Light marks an important step for any new telescope. It marks the first time that all of the telescope systems work together, including pointing, tracking (following objects in the sky), a polished and coated mirror, and a camera. While there often is still a lot of work to be done, first light means that the telescope construction is almost done, and that science can soon begin!

More versions of the above picture, as well as more detailed explanations of the photo and how it was taken, can be found here.

Tuesday, October 25, 2005

Dreaming of telescope time

It must be getting close to apply for more telescope time. Last night I dreamed that I had been appointed to the committee that assigns telescope time. It wasn't that exciting of a dream, to be honest.

Most people outside of astronomy have little idea how telescope time is assigned and used. Contrary to popular fiction, astronomers generally do not live on mountain tops, sleeping all day and working all night by staring through the eyepiece of a telescope. Except for the few astronomers hired to run telescopes, most of us work fairly normal hours at universities. We teach classes and do our research on computers, only rarely travelling to the mountains to use telescopes.

So, how do we get telescope time? The first part involves writing a proposal. We have to answer several questions. What science do we want to do? What star or galaxy do we want to look at? Why do we want to use this particular telescope? What cameras will we be using? How much time do we need to finish the science? What are the acceptable dates and times to use the telescope? And can we back all of this up with calculations?

Once each astronomer has written her/his proposal(s), the proposals are collected and sent to a "Time Allocation Committee," or TAC. The TAC must then read through the proposals and rank them. The rankings include a mix of how important the science is and how likely the project is to succeed. There are always proposals with great scientific ideas, but the proposed observations seem quite unlikely to succeed. Sometimes a project will definitely work, but the science isn't that exciting.

The TAC's job is a thankless task, because usually there are two to ten times more time requested than actually exists. So many good projects that are likely to succeed won't get time just because there isn't enough to go around. And how do you decide who gets time and who doesn't? It's pretty arbitrary a lot of the time.

Once the TAC is done, there is one last step -- the actual scheduling. The people who schedule the telescope use the TAC's rankings to guide their work. Often they can't schedule all of the highest-ranked proposals, though. Suppose there are two highly-ranked projects that will only succeed on May 23. Then the scheduler has to make a tough choice!

Anyway, that's how we get our time. It's a hard process, and even the best astronomers won't get all the time they want. But it pushes us to think hard about our projects and what we need to succeed.

Monday, October 24, 2005

Telescopes on the Moon? Part 2

The idea for a telescope on the moon is not new. There are advantages to a telescope on the moon. First, there is gravity, which makes the telescope design much cheaper than for space. Second, the moon is a stable platform. The gyroscopes that have caused headaches for the Hubble Telescope would not be needed -- a lunar telescope can point at a given point in space for years without needing any power or pointing at all. Finally, the lunar telescope will give our astronauts exploring the moon as part of NASA's Moon-Mars project something to do on the moon.

A lunar telescope would likely not have a glass mirror, like most telescopes on Earth, but a liquid mirror, like the Large Zenith Telescope in British Columbia, Canada. This mirror works by spinning liquid mercury in a large dish to make a thin layer in an exact parabolic shape. Many of the problems of such telescopes on Earth, such as the wind distorting the mirror, will not be a problem on the moon.

There are a few potential deal-breakers on a lunar telescope. First, the moon is a dusty place. There is some evidence that the moon may actually have an atmosphere made of dust. Obviously, you don't want dust landing in your liquid mirror, because you'll have to clean it! Second, a liquid-mirror telescope can only look in one direction -- up. If we build a telescope near the moon's north pole, we can always look at almost the same patch of sky. There are advantages to this, but if there is something we want to look at elsewhere in the sky, too bad!

With NASA's decision to go back to the moon and to Mars, the idea of a lunar telescope is being revived. Stay tuned!

Tuesday, October 18, 2005

A telescope on the moon?

This week Steward Observatory is having our annual "Internal Symposium." This is a two-day informal meeting where many of the astronomers, students, and other people associated with Steward come and give talks so we all know what each other is working on. It's a lot of fun, and we get a lot of talks on quite unrelated science.

Yesterday's highlights included a faculty member who is working on a design for a telescope on the moon, a talk about the International Dark Sky Association, discussions of the progress on building the Large Binocular Telescope, and even research into variations of Einstein's Relativity.

Later I'll talk more about the lunar observatory -- it's way cool.

Monday, October 10, 2005

Milky Way Bar

In the last few weeks, I got a question emailed from a reader of this blog (wow, I actually have a reader!). The question dealt with a new science report that the Milky Way has a larger bar than previously thought, and the reader wanted to know my opinion on the issue. Well, it's really quite simple. In order to raise flagging sales, the Mars Corporation has increased the size of a Milky Way chocolate bar from 1.2 ounces to 1.44 ounces net weight. (Just kidding!)

Spiral galaxies come in two basic flavors: "barred" and "non-barred." See if you can guess from these two images which is which:

It is hard to know the exact shape of the Milky Way, the galaxy our sun lives in, because we are in it. It is much like being in the middle of a dense forest and trying to figure out what its boundaries look like. In our galaxy, thick dust clouds block our view of the far parts of the galaxy. However, astronomers were able to use some clever techniques of measuring how fast stars are moving through space to deduce that our galaxy had at least a weak bar; perhaps something like this galaxy:

However, infrared light can go through much of this dust. The technology for studying large numbers of stars in the infrared has impoved dramatically over the last decade. Using this infrared light, astronomers were able to determine that our bar is in fact quite significant, perhaps something like this:

In this picture, our sun would be located about halfway between the center of the galaxy and the bright star near the lower right.

Friday, October 07, 2005

The Ig Nobel Prizes

Alas, blogging must be short today as I am in danger of missing deadlines.

As you know, every year the Nobel Prizes are awarded to scientists and scholars who have made extraordinary contributions to their fields. For 15 years, the Annals of Improbable Research has also awarded a prize, the Ig Nobel award, to scientists for research that cannot or should not be repeated. Sometimes this research is funny, sometimes it is just plain bizarre.

This year's winners and their achievements will soon be posted here. If you get a chance to watch the video of the prize ceremony, be sure to be on the lookout for real Nobel prize winners who often debase themselves by appearing at

Thursday, October 06, 2005

A visit to the Naval Observatory

Last week I had the pleasure of visiting the U.S. Naval Observatory in Flagstaff, Arizona. (Here is the Flagstaff Station website.)

The Naval Observatory was created for the purpose of doing astronomy and astronomical measurements that are vital for the Navy. This includes the positions of stars (for navigation), the exact time, and positions of the sun, moon and planets. Their mission statement outlines this, though I find the second part of point four to be darkly humorous. It reminds us that, although the USNO hires astronomers, it is still a branch of the military.

Most of the people at the Flagstaff station work on the positions, distances, and motions of stars. Yes, stars move, albeit usually much too slowly for people to detect. The "fastest" moving stars still take a thousand years to move a distance the size of the full moon through the sky. Still, these motions are important for understanding the structure of the Milky Way galaxy.

My thanks to the staff at the USNO for being such gracious hosts!