While Hubble Space Telescope (HST) is certainly the most famous observatory in space, it is by no means the only one. There have been dozens of space-based telescopes, including past missions like the highly successful Compton Gamma-Ray Observatory, which helped astronomers unravel some of the mysteries of gamma-ray bursts, and the currently operating Chandra X-Ray Observatory, which is exploring the violent regions around black holes and other high-energy phenomena.
Another member of NASA’s Great Observatories program is the Spitzer Space Telescope, which was launched in August 2003. It explores the infrared glow of stellar nurseries, planet-forming disks around newborn stars, and interstellar dust clouds.
The Kepler mission, launched in 2009, will spend three years looking for Earth-like planets in Earth-like orbits around Sun-like stars. It will scan 100,000 stars in the constellations Lyra and Cygnus in hopes of finding planetary transits, in which the star’s light dims slightly as a star passes across its disk.
NASA also has launched many smaller observatories through its Explorer program. These missions have probed the “afterglow” of the Big Bang (COBE and WMAP), the ultraviolet light from other galaxies (GALEX and EUVE), and the violent explosions known as gamma-ray bursts (SWIFT).