lunar image of the month

october: x-ray moon

These two X-ray images, taken by the ROSAT (Röntgensatellit) orbiting observatory, show the Moon occulting (eclipsing) a star. False colours show high energy X-rays in yellow and lower energy in red.

The star, called GX5-1, is a bright X-ray source shining with its own light, and in the background the general X-radiation of millions of distant stars and galaxies can be seen.

The Moon, of course, does not emit its own light, in the visible or the X-ray band of the spectrum. The left-hand hemisphere of the Moon shines with the reflected X-rays of the Sun. The radiation emitted from the darker right-hand hemisphere of the Moon is thought to be the result of high-energy particles in the solar wind bombarding the lunar surface, but this is still not clearly understood.