Explanation : 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. The bright X-ray sky is due to the diffuse cosmic X-ray background . The bright lunar crescent shines because it reflects X-rays emitted by the Sun . The dark lunar face is in shadow and so stands stands out from the relatively bright background - but, surprisingly it is not completely dark! Where do those X-rays from? They are currently thought to result from energetic particles from the solar wind bombarding the lunar surface.
Media Credits & Attribution
The X-Ray Moon Credit: DARA, ESA, MPE, NASA, J.H.M.M. Schmitt