Galex (Galaxy Evolution Explorer) is a space telescope launched on April 28, 2003. It was designed to study the evolution of galaxies in the ultraviolet wavelength range. The telescope’s primary mirror is 0.55m in diameter and has a field of view of 1 degree square. Galex observed more than 35,000 galaxies during its five-year mission.
Galex was a joint project of NASA and the California Institute of Technology. The telescope was built by Ball Aerospace & Technologies Corporation. The instrument used on Galex, the Near Ultraviolet Camera, was built by Hughes Danbury Optical Systems Incorporated.
The primary science goal of Galex was to map the history of star formation in galaxies over cosmic time. Star formation rates are highest in young galaxies and decrease as galaxies age. By mapping how these rates have changed over time, scientists can better understand how galaxies evolve. In addition to its imaging capabilities, Galex also spectroscopically surveyed about 1000 objects, including nearby starburst galaxies and distant quasars powered by black holes.
Galex’s observations were made possible by its unique sensitivity to ultraviolet light, which allows it to detect young hot stars that emit most of their radiation at these wavelengths. Most previous UV surveys had been limited by the atmospheric absorption of UV light, but Galex operated above 99% of Earth’s atmosphere from its orbit around Earth at an altitude of 613 kilometers (381 miles).
The spacecraft carried two identical 50 cm (19 inch) reflecting telescopes side-by-side with a separation between their lines-of-sight equal to that between a person’s eyes (approximately 64 mm or 2½ inches). This configuration allowed for very precise measurements of galaxy shapes and sizes as well as for removal of foreground stars within our own Milky Way Galaxy that would otherwise obscure faint background objects such as distant galaxies behind them. Each telescope focused UV light onto one 2048×2048 pixel charge coupled device detector; together the two detectors provided simultaneous views covering 0.65 square degrees or approximately 4 full moons worth of sky with each image taken