lunar image of the month

august: the moon in gamma rays

Gamma rays are a type of electromagnetic radiation - like visible light, but with 100,000 times the frequency. Even X-rays only have 1/100th of the frequency of gamma rays. Amazingly, if human vision was based on gamma rays instead of visible light, the Moon would actually appear much brighter than the Sun!

The majority of gamma rays are emitted by pulsars, quasars, radio galaxies, and other sources still not identified. The Sun is a very faint gamma ray source, but its cosmic radiation, which is stopped by the Earth's magnetic field, falls directly onto the lunar surface. This causes atomic decay which releases the gamma rays.

This image is a false-colour composite captured by EGRET, the Energetic Gamma Ray Experiment Telescope on NASA's Earth-orbiting Compton Gamma Ray Observatory.

Image: NASA.