Geological Chronicle
Located in the northwest quadrant of the lunar near side within the vast plains of Oceanus Procellarum, Aristarchus is the brightest large formation on the Moon. With an optical albedo of 0.18, more than double the lunar average, the 40-kilometer crater is bright enough to be seen with the naked eye from Earth and stands out clearly in earthshine. Its brilliance comes from its relative youth. Formed approximately 450 million years ago during the Copernican period, its excavated rocks have experienced relatively little space weathering from the solar wind.
The crater sits atop the Aristarchus Plateau, a 200-kilometer tilted rectangular crustal block elevated two kilometers above the surrounding mare basalts. The impact that formed Aristarchus struck at an oblique angle from the northeast, blasting bright ejecta rays to the south and southeast and penetrating deep into the lunar crust. Spectral data from the Clementine and Lunar Reconnaissance Orbiter missions revealed that its steep 860-meter central peak consists of pure anorthosite (plagioclase feldspar), while the surrounding terraced walls expose troctolite, a rock composed of plagioclase and olivine excavated from lower crustal layers.
The surrounding plateau preserves extensive pyroclastic dark mantling deposits, including a thick layer of iron- and titanium-rich volcanic glass beads, and is cleaved to the west by Vallis Schröteri, the largest sinuous rille on the Moon. In 1911, physicist Robert W. Wood photographed the plateau in ultraviolet light and found an anomalous dark patch known as "Wood's Spot", which modern spectral surveys identify as a sulfur- and ilmenite-rich volcanic deposit capable of supplying titanium and oxygen for future lunar infrastructure.
Aristarchus is also the historical center of reported Transient Lunar Phenomena, accounting for over one-third of all catalogued visual observations, including William Herschel's 1787 report of apparent volcanic fires during an eclipse. Orbital spectrometers have verified active gas venting at the site. The Alpha Particle Spectrometer on Apollo 15 detected radioactive radon-222 outgassing above the plateau in 1971, a finding later confirmed by NASA's Lunar Prospector in 1998, indicating the steady release of volcanic gases through deep crustal fractures.