Like the zodiacal light, the gegenschein is sunlight backscattered by interplanetary dust. Most of this dust is orbiting the Sun in about the ecliptic plane, with a possible concentration of particles at the L2 Earth–Sun Lagrangian point.
It is distinguished from zodiacal light by its high angle of reflection of the incident sunlight on the dust particles. It forms a slightly more luminous, oval glow directly opposite the Sun within the band of luminous zodiacal light. The intensity of the gegenschein is relatively enhanced, because each dust particle is seen in full phase.
The gegenschein was first described by the French Jesuit astronomer and professor Esprit Pezenas (fr) (1692–1776) in 1730. Further observations were made by the German explorer Alexander von Humboldt during his South American journey from 1799 to 1803. It was also Humboldt who gave the phenomenon its German name Gegenschein.
In modern times, the gegenschein is not visible in most inhabited regions of the world due to light pollution.
- Interplanetary dust cloud
- Earth's shadow
- Kordylewski cloud
- Opposition surge, the brightening of a rough surface, or an object with many particles, when illuminated from directly behind the observer
- Kopal, Zdeněk (June 14, 1962). "Communications on the Moon". New Scientist (291): 573.
- Levasseur-Regourd, Anny-Chantal; Hiroichi Hasegawa (1991). Origin and Evolution of Interplanetary Dust. International Astronomical Union Colloquium. p. 159. ISBN 0-7923-1365-8.
- Sheehan, William (1995). The immortal fire within: the life and work of Edward Emerson Barnard. Cambridge University Press. pp. 69–70. ISBN 0-521-44489-6.
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- Astrophotographs of the gegenschein
- "Zodiacal Light and the Gegenschein", an essay by J. E. Littleton
- Astronomy Picture of the Day, May 7, 2008
- Chisholm, Hugh, ed. (1911). "Gegenschein". Encyclopædia Britannica (11th ed.). Cambridge University Press.