Tuesday, July 05, 2005

Oh, It's Not An Interoceter; It's An Interferometer.

It was every exciting when the Mt. Palomar Observatory announced it would open its interoceter for public viewing. As any fan of 1950s science fiction movies knows, the interoceter is a machine from Metaluna, a planet inhabited by humanoids with really big foreheads and cool names like, "Exeter." In the classic movie, This Island Earth, the Metalunans send the plans and parts to build an interoceter to scientists on Earth as a test of intelligence. (Click here for IMDB webpage on movie and photos.) The scientists who successfully build an interoceter, Americans natch, are then recruited by the Metalunans to leave Earth and help them fight a war on their home planet. The movie is a cold war parable whose moral escapes me at the moment but it was probably something about the dangers of nuclear weapons, or science in service to militarism, or demonizing your enemies, or perhaps all three. It's a decent flick that has unfortunately been mercilessly skewered by Mystery Science Theater 3000.

I don't quite remember what an interoceter is or what it is supposed to do. I think it may have been some kind of subspace radio. It doesn't matter though, since Palomar either doesn't have one or they are still keeping it a secret from the public. Instead, they proudly opened their Palomar Testbed Interferometer to the public at the Open House.

The PTI is much different from the other scopes at the observatory. For one, it's not housed in a large dome like the others are. For two, it's not a single large scope but an array of smaller scopes that work in tandem to give the resolution of a much larger telescope.

The PTI's three 16 inch telescopes are housed in three small sheds separated by 110 meters.
When the scopes are operating the sheds roll back on tracks to expose them to the night sky.
The scopes are linked by vacuum tunnels to a central building.
The central building houses two mirrors on carts that move in tandem with the telescopes during operation. The light collected by the three small scopes is directed down the vacuum tunnels to the central mirrors, where the light is blended into a wave form that is captured by a special camera.

Because the scopes are each only 16 inchers they are not able to capture much light.
However, because they work in tandem and their light is blended in the central building they can duplicate the resolution of a much larger scope: about 4300 inches (110 meters) compared to Big Eye's 200 inches according to an astronomer at the Open House.

The PTI is thus able to measure objects with an accuracy unmatched by any other scope at the observatory. As one of the astronomers explained, the PTI could view an egg all the way across the United States in New York City and be able to tell which end of the egg was up. A neat parlor trick that would be.

The PTI was the first scope to accurately measure a star other than Sol. In this case, Altair, which turned out to be two times larger than Sol but spinning 600 times faster.

Today PTI is funded and managed by the Michelson Science Center. (Click here for Palomar's PTI webpage.) It is used to detect and measure the orbits of binary stars with very precise accuracy. It is also used to observe very young stellar objects. By observing these stellar infants, very much like Sol in its infancy, astronomers hope to learn about the early life of stars and about the disk material that surrounds stars and eventually forms planets.



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