Galaxy Evolution Explorer
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Galaxy Evolution Explorer(GALEX) A NASA ultraviolet space telescope launched into a nearly circular orbit Apr. 2003 for the purpose of observing ultraviolet radiation from a range of galaxies, both near and remote, in order to advance our knowledge of the evolution and history of galaxies and of star formation. In a 29-month mission supervised by the California Institute of Technology (Caltech), GALEX carried out an extragalactic all-sky survey to produce the first comprehensive map of the Universe showing galaxies evolving. To accomplish this, the observatory looked back in time to an era when the Universe was only 20% of its present age. The UV radiation from such remote regions is redshifted into the visible and near infrared, and the telescope made provision for this. By making a fair comparison between the remote galaxies observed at such an early period with ones close to us in both space and time, GALEX helped provide a means of assessing what changes have occurred between then and now so that cosmologists can learn when and where the stars and elements found today had their origins. GALEX was also tasked with identifying celestial objects for further investigation by current and future missions and producing an all-embracing publicly available archive of data.
The GALEX satellite weighed 280 kg. Its telescope was equipped with f/6 Richey-Chrétien optics. Its 50-cm-diameter primary mirror and 22-cm-diameter secondary mirror were especially coated to screen out local background radiation, and its observations were made only while it was in the Earth's shadow. The mirrors focused incoming light onto two 65-mm microchannel plate detectors with a total ultraviolet sensitivity range of 135–280 nm. The GALEX telescope produced wide-field circular images of sky measuring 1.2° in diameter at a resolution of 5 arcseconds in the far and near ultraviolet light bands. Spectra with 10 to 20 angstrom resolution for all objects within the field of view were obtained by placing a crystalline prism in the light path.