Opposition effect
The opposition effect (also known as the Seeliger effect) is an optical phenomenon in the form of an apparent brightening of surfaces at the opposite point of a light source. If, for example, the sun is behind an observer, the effect can be observed as a comparatively bright area around the opposite solar point on the ground.
In contrast to the halo , the opposition effect occurs on dry surfaces. The reason is that surface structures such as B. blades of grass, grains of sand, leaves etc. around the opposite point of a light source hide their own shadows from the observer. In addition, there is the effect of coherent backscattering .
The effect also plays a role in astronomy. Celestial bodies that do not have an atmosphere appear significantly brighter when they are exactly in opposition to the sun from the observer . The full moon, for example, is not twice as bright as the crescent moon, but more than ten times - in addition to the twice as large illuminated area, there is the increased surface brightness of the moon due to the opposition effect during the full moon phase. The effect was first observed by Tom Gehrels in 1956 on an asteroid. It could also be detected in the rings of Saturn.
Individual evidence
- ^ Opposition effect . on: meteoros.de
- ^ E. Akkermans, PE Wolf, R. Maynard: Coherent Backscattering of Light by Disordered Media: Analysis of the Peak Line Shape . In: Physical Review Letters . tape 56 , no. 14 , 1986, pp. 1471–1474 , doi : 10.1103 / PhysRevLett.56.1471 , PMID 10032680 , bibcode : 1986PhRvL..56.1471A .
- ^ J. Meeus: More Mathematical Astronomy Morsels. Willmann-Bell, Richmond 2002, ISBN 0-943396-74-3 . Cape. 7th
- ^ Opposition Surge. ( Memento of March 14, 2016 in the Internet Archive ) at: the-moon.wikispaces.com
- ↑ forum.astronomie.de