[ RadSafe ] " Gamma-Ray Earth "

Jaro jaro-10kbq at sympatico.ca
Sun Jun 4 18:49:38 CDT 2006

Gamma-Ray Earth

Credit: Dirk Petry (GLAST Science Support Center), EUD, EGRET, NASA

The pixelated planet above is actually our own planet Earth seen in gamma
rays - the most energetic form of light.
In fact, the gamma rays used to construct this view pack over 35 million
electron volts (MeV) compared to a mere two electron volts (eV) for a
typical visible light photon.
The Earth's gamma-ray glow is indeed very faint, and this image was
constructed by combining data from seven years of exposure during the life
of the Compton Gamma Ray Observatory, operating in Earth orbit from 1991 to
Brightest near the edge and faint near the center, the picture indicates
that the gamma rays are coming from high in Earth's atmosphere.
The gamma rays are produced as the atmosphere interacts with high energy
cosmic rays from space, blocking the harmful radiation from reaching the
Astronomers need to understand Earth's gamma-ray glow well as it can
interfere with observations of cosmic gamma-ray sources like pulsars,
supernova remnants, and distant active galaxies powered by supermassive
black holes.

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