NASA will soon be on the lookout for possible Earths in one faraway corner of the galaxy. A planet-hunting spacecraft, named “Kepler” after the German 17th-century astrophysicist, is scheduled to rocket away from Cape Canaveral, Fla., late Friday night. Excellent launch weather is forecast. The telescope will spend 3 1/2 years staring at roughly 100,000 stars, measuring their brightness and any winks in the light that might signify orbiting planets.
