Petrov is an

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...

along the southeastern limb of the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

. The crater is difficult to observe in this location, and visibility of this feature is affected by

libration In lunar astronomy, libration is the wagging or wavering of the Moon perceived by Earth-bound observers and caused by changes in their perspective. It permits an observer to see slightly different hemispheres of the surface at different tim ...

. The nearest crater of note is

Chamberlin The Chamberlin is an electro-mechanical keyboard instrument that was a precursor to the Mellotron. It was developed and patented by the American inventor Harry Chamberlin from 1949 to 1956, when the first model was introduced. There are severa ...

, just on the

far side ''The Far Side'' is a single-panel comic created by Gary Larson and syndicated by Chronicle Features and then Universal Press Syndicate, which ran from December 31, 1979, to January 1, 1995 (when Larson retired as a cartoonist). Its surrealis ...

to the northeast. Somewhat farther to the west-southwest of Petrov is

Gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

. The rim of this crater has been worn and eroded by impacts, leaving an irregular ring of ridges and incisions along the inner wall. The smaller crater Petrov A intrudes slightly into the southern rim. Along the southeast, Petrov B is attached to the southeastern exterior and the two are joined by a narrow valley. The interior floor of Petrov has been completely resurfaced by

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

, leaving a low-

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

surface that is relatively smooth and featureless. This material is nearly as dark as the

Mare Australe Mare Australe (Latin ''austrāle'' the "Southern Sea") is a lunar mare located in the southeastern hemisphere of the Moon. It is 997 kilometers in diameter, overlapping the near and far sides of the Moon. Smooth, dark volcanic basalt lines the ...

to the north. The floor is marked only by a few tiny craterlets.

Satellite craters

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Petrov.

References

* * * * * * * * * * * * {{refend Impact craters on the Moon