File:Moon in x-rays.gif

Summary
An image of the moon as seen in X-rays from X-ray fluorescence initiated by solar X-ray flux. Astronomy picture of the day caption: "This x-ray image of the Moon was made by the orbiting ROSAT (Röntgensatellit) Observatory on June 29, 1990. In this digital picture, pixel brightness corresponds to x-ray intensity. Consider the image in three parts: the bright hemisphere of the x-ray moon, the darker half of the moon, and the x-ray sky background. The bright lunar hemisphere shines in x-rays because it scatters x-rays emitted by the sun. The background sky has an x-ray glow in part due to the myriad of distant, powerful active galaxies, unresolved in the ROSAT picture but recently detected in Chandra Observatory x-ray images. The dark side of the Moon's disk shadows this X-ray background radiation coming from the deep space. But why isn't the dark half of the moon completely dark? New Chandra results also suggest that a few x-rays only seem to come from the shadowed lunar hemisphere. Instead, they originate in Earth's geocorona or extended atmosphere which surrounds the orbiting x-ray observatories." The measured lunar X-ray luminosity of ~ 1.2 x 1012 erg/s makes the Moon one of the weakest known non-terrestrial X-ray source. The scale on the picture says "16 arcmin".

Licensing
"Images from the X-ray sky taken with the ROSAT telescope. All rights reserved ©  Max-Planck-Institut für extraterrestrische Physik The X-ray images of MPE are produced by the SASS/EXSAS software MPE, ESO-MIDAS. The ROSAT project is managed by the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Germany on behalf of the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF)."