This X-Ray [ http://antwrp.gsfc.…] image of the Moon [ http://antwrp.gsfc.…] was made by the orbiting Roentgen Observatory Satellite (ROSAT [ http://heasarc.gsfc…]) 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 [ http://www.rosat.mp…]. The bright lunar crescent shines because it reflects X-rays emitted by the Sun [ http://antwrp.gsfc.…]. 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 [ http://www-spof.gsf…] bombarding the lunar surface.
