Kepler is NASA’s 10th Discovery mission. It is designed specifically to detect Earth-size planets orbiting in the habitable zone of solar-like stars. The telescope will stare continuously at over 100,000 stars in one region of the sky for 3 1/2 or more years looking for transits of planets, when they block a bit of light from their parent stars. From the amount of light blocked during the transit, scientists can calculate the size of the planet. Measuring the time between the transits , scientists can calculate the orbital period. Using Kepler’s Third Law of planetary motion, scientists then can calculate the distance the planet is from its star. The distance from the star largely determines the temperature of the planet and whether it may be habitable.