Gegenschein
Encyclopedia
The gegenschein (ˈɡeːɡənʃaɪn German
for "countershine") is a faint brightening of the night sky
in the region of the antisolar point
.
, 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 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
.
during his South American journey from 1799 to 1803. It was also Humboldt who gave the phenomenon its German name Gegenschein.
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.
Besides, Brorsen had already proposed the correct explanation for the gegenschein (interplanetary dust reflections).
German language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....
for "countershine") is a faint brightening of the night sky
Night sky
The term night sky refers to the sky as seen at night. The term is usually associated with astronomy, with reference to views of celestial bodies such as stars, the Moon, and planets that become visible on a clear night after the Sun has set. Natural light sources in a night sky include moonlight,...
in the region of the antisolar point
Antisolar point
The antisolar point is the imaginary point on the celestial sphere exactly opposite the Sun. It is where anticrepuscular rays appear to converge, and on a moonless night away from city lights, it is often possible to see the gegenschein there. The apex of a rainbow will also form roughly 42...
.
Explanation
Like the zodiacal lightZodiacal light
Zodiacal light is a faint, roughly triangular, whitish glow seen in the night sky which appears to extend up from the vicinity of the sun along the ecliptic or zodiac. Caused by sunlight scattered by space dust in the zodiacal cloud, it is so faint that either moonlight or light pollution renders...
, the gegenschein is sunlight reflected by interplanetary dust. Most of this dust is orbiting the Sun in about the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
plane, with a possible concentration of particles at the Earth–Sun Lagrangian point
Lagrangian point
The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...
.
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
Lunar phase
A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
.
History
The gegenschein was first described by the French Jesuit astronomer and professor Esprit Pézenas (1692–1776) in 1730. Further observations were made by the German explorer Alexander von HumboldtAlexander von Humboldt
Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...
during his South American journey from 1799 to 1803. It was also Humboldt who gave the phenomenon its German name Gegenschein.
The Danish astronomer Theodor Brorsen
Theodor Brorsen
Theodor Johan Christian Ambders Brorsen was a Danish astronomer best known for his discovery of five comets, including the lost periodic comet 5D/Brorsen and the periodic comet 23P/Brorsen-Metcalf.- Life :...
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.
Besides, Brorsen had already proposed the correct explanation for the gegenschein (interplanetary dust reflections).
See also
- Zodiacal lightZodiacal lightZodiacal light is a faint, roughly triangular, whitish glow seen in the night sky which appears to extend up from the vicinity of the sun along the ecliptic or zodiac. Caused by sunlight scattered by space dust in the zodiacal cloud, it is so faint that either moonlight or light pollution renders...
- Zodiacal dustZodiacal dustThe Zodiacal dust cloud is visible as a diffuse glow, known as the zodiacal light, that stretches along the zodiac, and is best seen just after sunset and before sunrise in spring and autumn when the zodiac is at a steep angle to the horizon....
- Interplanetary dust cloudInterplanetary dust cloudThe interplanetary dust cloud is cosmic dust which pervades the space between planets in the Solar System and in other planetary systems...
- Earth's shadowEarth's shadowThe Earth's shadow or Earth shadow are names for the shadow that the Earth itself casts on its atmosphere. This shadow is often visible from the surface of the Earth, as a dark band in the sky near the horizon...
- HeiligenscheinHeiligenscheinHeiligenschein is an optical phenomenon which creates a bright spot around the shadow of the viewer's head. It is created when the surface on which the shadow falls has special optical characteristics. Dewy grass is known to exhibit these characteristics, and creates a Heiligenschein...
- SylvanshineSylvanshineSylvanshine is an optical phenomenon in which dew-covered trees of species whose leaves are wax-covered retroreflect beams of light, as from a vehicle's headlights, sometimes causing trees to appear to be snow-covered at night during the summer. The phenomenon was named and explained in 1994 by...
- Kordylewski cloudKordylewski cloudKordylewski clouds are large concentrations of dust that may exist at the and Lagrangian points of the Earth–Moon system. They were first reported by Polish astronomer Kazimierz Kordylewski in the 1960s, but there is still controversy as to whether they actually exist, due to their extreme...