Gegenschein

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Gegenschein (German for counterglow) is a faint brightening of the night sky in the region of the ecliptic directly opposite the Sun. It was discovered in 1854 by the Danish astronomer Theodor Brorsen.

[edit] Observation

The gegenschein is so faint that it cannot be seen if there is any moonlight or light pollution, or if it falls in the vicinity of the Milky Way. The gegenschein appears as a softly glowing oval region a few degrees wide and 10-15° in length, oriented along the plane of the ecliptic.

[edit] Explanation

Like the zodiacal light the gegenschein is sunlight reflected by interplanetary dust. Most of this dust is orbiting the sun in about the ecliptic plane (zodiac). The intensity of gegenschein is (relatively) enhanced because (a) each dust particle is seen in full phase, and (b) the backscattering geometry leads to constructive interference.