The Kepler spacecraft and its Delta II rocket successfully escaped Earth's atmosphere, launching from Launch Complex 17-B at Cape Canaveral Air Force Station at 10:49 p.m. EST on March 6.
The Kepler spacecraft will watch a patch of space for 3.5 years or more for signs of Earth-sized planets moving around stars similar to the sun. The patch that Kepler will watch contains about 100,000 stars like the sun. Using special detectors similar to those used in digital cameras, Kepler will look for slight dimming in the stars as planets pass between the star and Kepler.
Kepler has the largest camera ever launched into space, a 95-megapixel array of charge-coupled devices.
Kepler mission homepage.
Kepler mission overview from NASA.