... ROSAT Explores The X-Ray Sky . ... Launched in 1990, the orbiting ROSAT observatory explored the Universe by viewing the entire sky in x-rays - photons with about 1,000 times more energy than visible light. ... A Close-Up of the Horsehead Nebula . ... The X-Ray Moon . ... This X-Ray image of the Moon was made by the orbiting Roentgen Observatory Satellite (ROSAT) in 1990. It shows three distinct regions: a bright X-ray sky, a bright part of the Moon, and a relatively dark part of the Moon. ...