Fermi Science Standoff
Sun and Moon in Gamma-rays

The Sun and Moon in Gamma-rays
(click image for full size)

The Moon is brighter than the Sun -- in gamma-rays! This image depicts the Sun (left) and the Moon (right) as seen in gamma-rays using data collected by the Fermi Large Area Telescope. The inset images show the respective objects at longer, more familiar optical wavelengths where the Sun outshines the Moon by a large factor.

The Moon is so bright in gamma-rays because high-energy charged particles called cosmic rays are constantly striking its surface, which is unprotected by a magnetic field. This generates the gamma-ray glow that is evident in the false color map, in which the brightest pixels represent the most significant detections of gamma-rays from the Moon. Since the cosmic rays come from all directions, the gamma-ray Moon is always full and does not go through the phases that we see with our eyes. The Sun has a magnetic field, and it deflects some of the cosmic rays, so it shines less brightly in gamma-rays.

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