When Galileo used his homemade telescope 400 years ago to view mountains on the Moon, satellites circling Jupiter, and the myriad of stars in our Milky Way Galaxy, he launched a revolution that changed our view of an Earth-centered universe. The launch of the Hubble Space Telescope aboard the space shuttle Discovery on April 24, 1990 initiated another revolution in astronomy. For the first time, a large telescope that sees in visible light began orbiting above Earth's distorting atmosphere. Astronomers anticipated great discoveries from Hubble. The telescope has delivered as promised and continues serving up new discoveries.