Kepler
Discovering planets that orbit other stars is hard work. Astronomers can't see the planets directly. Instead, they look for tiny changes in a star's light. The most common technique looks for "wiggles" in the light caused by the gravity of an orbiting planet. This technique has led to the discovery of about 150 planets -- most of them giant worlds that are close to their stars.
Astronomers also have detected a few planets by watching as a star's light periodically fades a tiny bit -- the result of a planet crossing in front of the star and blocking a little of its light.
Such crossings are called transits. They'll allow astronomers to find Earth-like planets in Earth-like orbits.
A spacecraft scheduled for launch in 2008 is designed to detect many such planets. The craft is called Kepler. It'll keep a constant eye on a patch of sky that's about twice the size of the bowl of the Big Dipper. Its target region is in the constellations Cygnus and Lyra, which are low in the west-northwest on December evenings.
Kepler will monitor about a hundred thousand stars that are like the Sun in that region, looking for periodic changes in their light. That should lead to the discovery of hundreds of planets.
Kepler's measurements will tell us how big the planets are, and how far they are from their parent stars. That information will reveal something even more important: whether the planets are at the right temperature for water -- and life.
Script by Damond Benningfield, Copyright 2005
For more about the Kepler Mission, visit NASA's website at http://kepler.nasa.gov.
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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