Benoit Morrissette wrote:

On Wed, 20 Oct 2004 07:09:59 -0400, (G=EMC^2
Glazier) wrote:

Astronomers use eclipses lots of ways. In binary systems they can tell
how fast they are circling each other. We might get lucky someday and
find a planet making a total eclipse of its sun.

Sorry for the cold shower but that is not possible unless the planet
is at least as big as it's star. It is a matter of visual
perspective. The Moon does eclipse the Sun because the Moon is near
us and the Sun is far away from us. If both were at the same distance
from us, we would see them both in their relative size. When we look
at an extra solar system, the star and it's planets are essentially at
the same distance from us!


Plenty of eclipsing binary stars have been observed, though; I
believe Algol, Beta Persei, is about the brightest. See

http://www-astro.physics.uiowa.edu/~lam/research/algol/mov2.html.

--
Odysseus