... ROSAT Explores The X-Ray Sky . ... Credit: S. Digel and S. Snowden ( GSFC ), ROSAT Project , MPE, NASA Explanation: 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 . This ROSAT survey produced the sharpest, most sensitive image of the x-ray sky to date. The all-sky image is shown with the plane of our Milky Way Galaxy running horizontally through the center. ...