- Aristarchus (crater)
lunar crater data
caption=Aristarchus (center) and Herodotus (right) from
Apollo 15. " NASAphoto".
Aristarchus is a prominent lunar
impact craterthat lies in the northwest part of the Moon's near side. It is considered the brightest of the large formations on the lunar surface, with an albedonearly double that of most lunar features. The feature is bright enough to be visible to the naked eye, and is dazzling in a large telescope. It is also readily identified when most of the lunar surfaceis illuminated by earthshine.
The crater is located at the southeastern edge of the Aristarchus plateau, an elevated area that contains a number of volcanic features, such as sinuous
rilles. This area is also noted for the large number of reported transient lunar phenomena, as well as recent emissions of radongas as measured by the Lunar Prospectorspacecraft.
Aristarchus was originally named after the Greek astronomer
Aristarchus of Samosby the Italian map maker Giovanni Riccioli. His work "Almagestum novum" ("New Almagest"), published in 1651, gave the spot-shaped telescopic features (later called "craters") eponyms of noted astronomers and philosophers. Although it was already widely adopted, the name didn't become an official international standard until a vote by the IAU General Assembly in 1935. [cite book | author=M. A. Blagg, K. Müller, W. H. Wesley, S. A. Saunder, J. H. G. Franz | title=Named Lunar Formations | publisher=Percy Lund, Humphries & Co. Ltd. | location=London | year=1935 | url=http://adsabs.harvard.edu/abs/1935QB595.B6....... ]
Aristarchus is located on an elevated rocky rise, known as the Aristarchus plateau, in the midst of the
Oceanus Procellarum, a large expanse of lunar "mare". This is a tilted crustal block, about 200 km across, that rises to a maximum altitude of 2 km above the "mare" in the southeastern section.cite web | url = http://www.lpi.usra.edu/resources/clemen/cmaris.html | title = Aristarchus Region: Multispectral Mosaic of the Aristarchus Crater and Plateau | publisher = Lunar and Planetary Institute |accessdate = 2006-08-08 ] Aristarchus is just to the east of the crater Herodotus and the Vallis Schröteri, and south of a system of narrow sinuous rilles named Rimae Aristarchus.
The main reason for the crater's brightness is that it is a young formation, approximately 450 million years old, and the
solar windhas not yet had time to darken the excavated material by the process of space weathering. The impact occurred following the creation of the ray crater Copernicus, but before the appearance of Tycho.
The brightest feature of this crater is the steep central peak. Sections of the interior floor appear relatively level, but
Lunar Orbiter photographs reveal the surface is covered in many small hills, streaky gouges, and some minor fractures. The crater has a terraced outer wall, roughly or polygonal in shape, and covered in a bright blanket of ejecta. These spreads out into bright rays to the south and south-east, suggesting that Aristarchus was most likely formed by an oblique impact from the northeast, and their composition includes material from both the Aristarchus plateau and the lunar mare.
In 1911, Professor Robert W. Wood used
ultraviolet photographyto take images of the crater area. He discovered the plateau had an anomalous appearance in the ultraviolet, and an area to the north appeared to give indications of a sulfurdeposit.cite web | last = Darling | first = David O. | url = http://www.ltpresearch.org/aristarchus1.htm | title = Aristarchus: Lunar Transient Phenomenon History | publisher = L.T.P. Research | accessdate = 2006-08-08 ] This colorful area is sometimes referred to as "Wood's Spot", an alternate name for the Aristarchus Plateau.
Spectra taken of this crater during the
Clementine missionwere used to perform mineralmapping. The data indicated that the central peak is a type of rock called anorthosite, which is a slow-cooling form of igneousrock composed of plagioclase feldspar. By contrast the outer wall is troctolite, a rock composed of equal parts plagioclaseand olivine.
The Aristarchus region was part of a
Hubble Space Telescopestudy in 2005 that was investigating the presence of oxygen-rich glassy soils in the form of the mineral ilmenite. Baseline measurements were made of the Apollo 15and Apollo 17landing sites, where the chemistry is known, and these were compared to Aristarchus. The Hubble Advanced Camera for Surveys was used to photograph the crater in visual and ultravioletlight. The crater was determined to have especially rich concentrations of ilmenite, a titanium oxidemineral that could potentially be used in the future by a lunar settlement for extracting oxygen. [cite web | title=Is There Oxygen on the Moon? | work=Time Online
url=http://www.time.com/time/health/article/0,8599,1120755,00.html | accessmonthday=October 24 | accessyear=2005]
Transient lunar phenomena
The region of the Aristarchus plateau has been the site of many reported
transient lunar phenomena. Such events include temporary obscurations and colorations of the surface, and catalogues of these show that more than one-third of the most reliable spottings come from this locale.cite web | url=http://www.cs.nott.ac.uk/~acc/Lunar/cameron.pdf | last = W. Cameron | title=Analyses of Lunar Transient Phenomena (LTP) Observations from 557–1994 A.D.] In 1971 when Apollo 15passed 110 kilometers above the Aristarchus plateau, a significant rise in alpha particles was detected. These particles are believed to be caused by the decay of radon-222, a radioactive gaswith a half-lifeof only 3.8 days. The Lunar Prospectormission later confirmed Radon-222 emissions from this crater. [cite journal|last = S. Lawson, W. Feldman, D. Lawrence, K. Moore, R. Elphic, and R. Belian | title=Recent outgassing from the lunar surface: the Lunar Prospector alpha particle spectrometer | journal=J. Geophys. Res. | volume = 110 | pages=doi=10.1029/2005JE002433 | date =2005|doi = 10.1029/2005JE002433 | date =2005] These observations could be explained by either the slow and visually imperceptible diffusion of gas to the surface, or by discrete explosive events.
Surrounding Aristarchus are several smaller craters, many of which are probably
secondary craters. Secondary craters form when large blocks ejected from the primary crater reimpact the surface at high velocities. By convention these features are identified on lunar maps by placing a letter on the side of the crater mid-point that is closest to the primary crater. [cite book | author=B. Bussey & P. Spudis | title=The Clementine Atlas of the Moon | publisher=Cambridge University Press | year=2004 | id=ISBN 0-521-81528-2 ]
The following craters have been renamed by the IAU.
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Aristarchus — may refer to: * Aristarchus (crater), on the moon * Aristarchus of Samos (circa 310 230 BC), Greek astronomer and mathematician * Aristarchus of Samothrace (circa 220 143 BC), Greek grammarian * Aristarchus of Tegea (5th century BC), Greek writer … Wikipedia
Aristarchus (Cratère) — Aristarchus Aristarchus à gauche vu par Apollo 15. Localisation Astre Lune … Wikipédia en Français
Aristarchus (cratere) — Aristarchus (cratère) Aristarchus Aristarchus à gauche vu par Apollo 15. Localisation Astre Lune … Wikipédia en Français
Aristarchus of Samos — [ar΄is tär′kəs] fl. 3d cent. B.C.; Gr. astronomer * * * born с 310 BC died с 230 BC Greek astronomer. His advanced ideas on the movement of the Earth (which he asserted revolved around the Sun) are known from Archimedes and Plutarch. His only… … Universalium
Aristarchus (cratère) — Aristarchus Aristarchus (à gauche) et Herodotus (à droite) vus par Apollo 15. Localisation Astre … Wikipédia en Français
Aristarchus — noun 1. an ancient Greek grammarian remembered for his commentary on the Iliad and Odyssey (circa 217 145 BC) • Instance Hypernyms: ↑grammarian, ↑syntactician 2. a bright crater on the Moon • Instance Hypernyms: ↑lunar crater … Useful english dictionary
Aristarchus — /ar euh stahr keuhs/, n. 1. of Samos. late 3rd century B.C., Greek astronomer. 2. of Samothrace. c216 144 B.C., Greek philologist and critic. 3. an extremely bright crater in the second quadrant of the face of the moon: about 29 miles (47 km) in… … Universalium
Aristarchus — /ærəsˈtakəs/ (say aruhs tahkuhs) noun a crater in the north eastern quadrant of the moon … Australian English dictionary
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