Artist Concept of Galaxy Evolution Explorer

The Galaxy Evolution Explorer was launched on April 28, 2003. Its mission is to study the shape, brightness, size and distance of galaxies across 10 billion years of cosmic history. The 50-centimeter-diameter (19.7-inch) telescope onboard the Galaxy Evolution Explorer sweeps the skies in search of ultraviolet-light sources.

Ultraviolet is light from the higher end of the electromagnetic spectrum, just above visible light in frequency, but below X-rays and gamma rays. While a small amount of ultraviolet penetrates Earth's atmosphere, causing sunburn, the Galaxy Evolution Explorer observes those ultraviolet frequencies that can only be seen from space.

http://photojournal.jpl.nasa.gov/catalog/PIA04234