Kordylewski clouds are large concentrations of dust that may exist at the L4 and L5 Lagrangian points of the Earth–Moon system. They were first reported by Polish astronomer Kazimierz Kordylewski in the 1960s, but there is still debate as to whether they actually exist, due to their extreme faintness. They may be transient phenomena, as the L4 and L5 points are unstable, due to the perturbations of the inner planets.
Discovery and observation 
The clouds were first seen by Kordylewski in 1956. Between 6 March and 6 April, 1961 he succeeded in photographing two bright patches near the L5 libration point. During the observation time the patches hardly appeared to move relative to L5. The observations were taken from the mountain Kasprowy Wierch.
The existence of the Kordylewski clouds is still under dispute. The Japanese Hiten space probe, which passed through the libration points to detect trapped dust particles, did not find an obvious increase in dust levels above the density in surrounding space.
The Kordylewski clouds are a very faint phenomenon, comparable to the brightness of the gegenschein. They are very difficult to observe from Earth but may be visible to the unaided eye in an exceptionally dark and clear night sky. Most claimed observations have been made from deserts, at sea, or from mountains. The clouds appear somewhat redder than the gegenschein, indicating that they may be made of a different kind of particle.
The Kordylewski clouds are located near the L4 and L5 Lagrange points of the Earth–Moon system. They are about 6 degrees in angular diameter. The clouds can drift up to 6 to 10 degrees from those points. Other observations suggest they move around the libration points in ellipses of about 6 by 2 degrees.
See also 
- Kordylewski, Kazimierz (1961). "Photographische Untersuchungen des Librationspunktes L5 im System Erde-Mond". Acta Astronomica (in German) 11: 165–169. Bibcode:1961AcA....11..165K.
- Laufer, Rene; Wilfried Tost, Oliver Zeile, Ralf Srama, Hans-Peter Roeser (February 2007). "The Kordylewsky Clouds — an Example for a Cruise Phase Observation During the Lunar Mission BW1" (pdf). 11th ISU Annual International Symposium. Strasbourg. http://www.wfs.be.schule.de/pages/Mondbeobachter/Daten/KordylewskiClouds-Paper.pdf. Retrieved 2009-01-07.
- "Hiten". NASA. Retrieved 2009-03-08.
- Covington, Michael A. (1999). Astrophotography for the Amateur. Cambridge University Press. pp. 32–33. ISBN 0-521-62740-0.
- Kazimierz Kordylewski (1961). "Photographische Untersuchungen des Librationspunktes L5 im System Erde-Mond". Acta Astronomica 11: 165–169. Bibcode:1961AcA....11..165K.
- "Dust Cloud Moons of the Earth". Physics Today 2: 39–46. 1967.
- Winiarski, Maciej (1989). "Photographic Observations of the Clouds in the Neighbourhood of Libration Point L5 of the Earth-Moon System". Earth, Moon and Planets 47 (2): 193–215. Bibcode:1989EM&P...47..193W. doi:10.1007/BF00058142.
- Hypothetical Planets
- A Search for Objects near the Earth-Moon Lagrangian Points, by Francisco Valdes and Robert A. Freitas Jr., did not find any objects at the Earth-Moon or Earth-Sun lagrange points, but this survey was not sensitive to diffuse clouds.
- Counterglow from the earth-moon libration points, by Roach, J. R., 2004-11-03, retrieved in 2010-11-28.