Monday, November 21, 2005
Wednesday, November 16, 2005
You haven't seen much from me recently, as it is time for me to hunt for jobs. Many parts of applying for astronomy jobs are the same as applying for jobs in the "real" world. We put together our resumes, write cover letters, and scour specific magazines and web sites for job advertisements. Most people apply to a whole slew of openings, hoping to get a couple of nibbles.
But there are major differences, too. First, most job openings are announced in the fall for work starting the following summer or fall. This is driven by the academic calendar, as most jobs are affiliated with universities. This also means the hiring process is quite slow, as job hires have to go through several layers of bureaucracy.
Applications are read by a committee in the department. This committee pares down the list to a select few for interviews. Then the list has to be approved by a higher official, such as the college dean. After the dean gives the list approval, people on the list are invited for interviews and to give talks on their research to the entire department. After the interviews, the committee will rank the applicants, and the entire faculty of the department select their nominee. Once again the dean has to approve, and then the compensation package must be drawn up, usually by some other part of university bureaucracy. What fun! And it takes months to finish!
So, for now, I'm busy writing all those cover letters. We'll see how things turn out.
Monday, November 07, 2005
News reports from Germany and Alaska have mentioned an abundance of "UFOs" seen in the sky in the past few weeks. Is Earth being invaded? Is it time to break out your Klingon-English dictionary in the hopes that you can save yourself with some friendly banter?
Whoa, slow down. Let's approach this thing scientifically, which means that, before invoking the Borg Cube to explain these events, we need to rule out more likely explanations. What are things that people commonly mistake for UFOs?
- Planets: Planets, especially Venus and Mars, are often mistaken for UFOs. Right now Venus is dazzlingly bright in the west after sunset, and Mars is bright and orange in the east during the evening. When low in the sky, planets can look like they are "hovering" over the ground, and they can appear to be flashing colors due to the atmosphere. I once had a TV crew try to convince me that they had a UFO slowly landing in the Pacific on video tape. I recognized where their tape had been made, and their tape had a time stamp. A little playing around with a planetarium program showed that they had just seen Venus setting in the ocean. But, the German and Alaskan witnesses said the lights were moving in the sky, whereas the planets move much more slowly. So they didn't see planets.
- Airplanes: Airplanes move across the sky, and when they have their landing lights on, they appear very bright. A surprising number of people don't recognize airplanes in the sky. But airplanes take several minutes to cross the sky, and the lights in Germany move across the sky in seconds.
- Satellites: Low-earth orbiting satellites move across the sky in only a couple of minutes, and some can be very bright (the Space Station and Space Shuttle can be brighter than the brightest star in the sky). Satellites can also appear to do sudden changes in direction. This is an optical illusion, but I've seen this illusion with my own eyes many times. Satellites can also appear to flash if they are tumbling out of control or if the sun mirrors off of odd-shaped corners. However, the bright things in Germany and Alaska crossed the sky in seconds, not minutes.
- Meteors: Meteors ("shooting stars") can be very bright (these are called "fireballs"), and they can cross the entire sky in seconds. They can also leave behind glowing trails, called "trains", which can last up to a minute or more! The descriptions of the eyewitnesses to these "UFOs" match meteors exactly. So, I think it is safe to say that space dust, and not aliens, are the cause of the ruckus.
So, why so many sightings all at once? This time of year the Earth moves through the orbit of Comet Encke. Comet Encke orbits the sun every three years, but rarely comes close to Earth. However, every time the comet comes close to the sun, little bits of dust and rock come off of it. These bits of dust and rock continue to orbit the sun, but slowly get spread over the comet's entire orbit. Every November, when the Earth passes through the comet's orbit, we sweep up some of the dust and rocks, making for a meteor shower. The meteors from Encke appear to come from the constellation Taurus, and so the meteor shower is called the "Taurids."
Normally the Taurids are a pretty weak stream, with fewer than 10 meteors per hour visible from any one spot. This year the Earth seems to be passing through a denser part of the comet's debris, so we are seeing more meteors than normal. The Taurids have a history of sometimes producing many fireballs, and this seems to be one of those years!
Thursday, November 03, 2005
I saw on the news today that the Milky Way's black hole is smaller than previously thought. This made me perk up, because the word "smaller" can mean physical size (like a foot is smaller than a mile), or it can mean mass (like a pound of brick is smaller than a ton of brick).
My first reaction was that the word "smaller" meant "less massive," especially since the physical size of a black hole is kind of a fuzzy comment. This is why I perked up. Astronomers have been able to make some very accurate measurements of the mass of our galaxy's black hole: about 2 million times the mass of the sun. These measurements are based on the movement of stars around the black hole, and physics from Isaac Newton in the 17th century is sufficient to figure out the mass of the black hole. So if its mass were smaller, this would be quite surprising.
But it is not the mass that is smaller, it is the physical size. Astronomers using radio telescopes on Earth were able to make the sharpest picture of the gas around the black hole yet made. They were able to resolve details only 93 million miles across, or the size of Earth's orbit around the sun. Not bad for taking this picture from 24,000 light-years away!
We are still fairly far outside the edge of the black hole, though. The black hole's event horizon is still at least 12 times smaller than this picture. So we still haven't "seen" the black hole, but we are pretty close!
Wednesday, November 02, 2005
Pluto, the most distant planet in the solar system, was discovered in 1930 by Clyde Tombaugh. It was not until 1978 that astronomer James Christy discovered Pluto's moon Charon while observing at the U.S. Naval Observatory in Flagstaff, Arizona. Charon orbits Pluto every 6.4 days. Astronomers like to study Charon, because its orbit around Pluto helps us to learn more about Pluto, like its mass, actual size, and composition.
As part of these studies, Pluto and Charon were imaged by the Hubble Space telescope in May 2005. A team led by Alan Stern of the Southwest Research Institute and Hal Weaver of Johns Hopkins University saw two "stars" that moved with Pluto and also appeared to be orbiting it. There is only one explanation for this -- these "stars" are really two new moons of Pluto!
Moons are very common in the solar system. The only planets without moons are Venus and Mercury. Even many asteroids and other icy objects in the Kuiper Belt have moons.
So congratulations to Pluto on its new moons. The International Astronomical Union will be considering names for the moons (the discovery team gets first crack at appropriate names) in the near future.