On March 7, 2009 the Kepler Space Telescope was launched by NASA to discover Earth-size planets orbiting stars other than the Sun. Named after astronomer Johannes Kepler, the spacecraft was put into into orbit around the Sun trailing the Earth. NASA announced its retirement on October 30, 2018 when its fuel was depleted.
The telescope surveyed a portion of Earth’s region of the Milky Way to discover Earth-sized in or near habitable zones. It was also tasked with finding out how many starts have such planets.
Beautiful in its simplicity, Kepler’s sole scientific instrument was a photometer that continually monitored the brightness the stars in its range of view. Periodic dimming of the host start indicated a planet. During its over nine years of service, Kepler observed 530,506 stars and detected 2,662 planets.
The Kepler Telescope arguably gave more data to more fields of astronomy than any other single venture. ATTENTION TEACHERS: NASA has a wealth of educational material about the Kepler Telescope available for all grade levels. Look here.