ROSAT Explores The X-Ray Sky . ... Credit Copyright: S. Digel and S. Snowden ( USRA / LHEA / 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. ... The all-sky image is shown with the plane of our Milky Way Galaxy running horizontally through the center. ... Bright x-ray spots near the galactic plane are within our own Milky Way. ...