Gegenschein

The gegenschein in a fish-eye view of the night sky above the Paranal Observatory.

The gegenschein (German pronunciation: [ˈɡeːɡənʃaɪn] German for "countershine") is a faint brightening of the night sky in the region of the antisolar point.

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, with a possible concentration of particles at the L₂ Earth-Sun Lagrangian point.^[1]

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.^[2]

History

The gegenschein was first described by the French Jesuit astronomer and professor Esprit Pézenas (1692–1776) in 1730.^[3] Further observations were made by the German explorer Alexander von Humboldt during his South American journey from 1799 to 1803.^[3] It was also Humboldt who gave the phenomenon its German name Gegenschein.^[3]

The Danish astronomer Theodor Brorsen published the first thorough investigations of the gegenschein in 1854. He was also the first to observe that the zodiacal light can embrace the complete sky, because under near-perfect conditions a feeble light bridge connecting the zodiacal light and the gegenschein can be observed.^{[citation needed]} Besides, Brorsen had already proposed the correct explanation for the gegenschein (interplanetary dust reflections).

See also

• Zodiacal light
• Zodiacal dust
• Interplanetary dust cloud
• Earth's shadow
• Heiligenschein
• Sylvanshine
• Kordylewski cloud

References

1. ^ Kopal, Zdeněk (June 14 1962). "Communications on the Moon". New Scientist (291): 573. 
2. ^ Levasseur-Regourd, Anny-Chantal; Hiroichi Hasegawa (1991). Origin and Evolution of Interplanetary Dust. International Astronomical Union Colloquium. p. 159. ISBN 0-7923-1365-8. 
3. ^ ^{a b c} 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. 

External links

• 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.