NASA Astronomy Picture of the Day Collection

X-Ray Moon

This x-ray image [ http://heasarc.gsfc…misc_moon2.html ] of the Moon [ http://antwrp.gsfc.…] was made by the orbiting ROSAT [ http://heasarc.gsfc…] (Röntgensatellit [ http://heasarc.gsfc…wilhelm.html ]) Observatory in 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 [ http://antwrp.gsfc.…] background. The bright lunar hemisphere shines in x-rays [ http://imagine.gsfc…history1_xray.html ] because it reflects x-rays emitted by the sun ... just as it shines at night [ http://antwrp.gsfc.…] by reflecting visible sunlight. The background [ http://heasarc.gsfc…background/backgroun d.html ] 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 [ http://antwrp.gsfc.…]. But why isn't the dark half of the moon completely dark? It's true that the dark lunar face is in shadow [ http://antwrp.gsfc.…] and so is not reflecting solar x-rays [ http://antwrp.gsfc.…]. Still, the few x-ray photons which seem to come from the moon's dark half are currently thought to be caused by energetic particles in the solar wind [ http://www-spof.gsf…] bombarding the lunar surface.

J. Schmitt et al., ROSAT Mission [ http://www.xray.mpe…], MPE [ http://www.mpe.mpg.…], ESA [ http://www.esrin.es…]

moon

x-rays

cosmic rays

x-ray background

1990

Goddard Space Flight Center (GSFC)

Washington, D.C.

Moon

Sun

ROSAT

moon

1990

http://antwrp.gsfc.…

SPD-APOD-ap000902