Ritter (crater)

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The crater pair Sabine (center right) and Ritter (right), from Apollo 11
Coordinates2°00′N 19°12′E / 2.0°N 19.2°E / 2.0; 19.2Coordinates: 2°00′N 19°12′E / 2.0°N 19.2°E / 2.0; 19.2
Diameter29 km
Depth1.3 km
Colongitude341° at sunrise
EponymCarl Ritter
Georg August Dietrich Ritter
Lunar Orbiter 4 image of Sabine (right of center), Ritter (left of center), and Schmidt (lower left) craters

Ritter is a lunar impact crater located near the southwestern edge of Mare Tranquillitatis and are named after Carl and Georg August Dietrich Ritter. It is the northwestern member of a crater pair with Sabine about 3 km southeast.

Its diameter is 29 km long which is shorter than the partner crater and is 1,300 meters deep which is roughly the same. Also, the area is around 675 km² and the perimeter is over 90 km.

From that location the Earth would appear in the lunar sky at over 2 degrees from the top and it is seen more than 19 degrees towards the west.

Apollo 10 image of Ritter


The two rims are separated by a narrow valley only a couple of kilometers wide. About half a crater diameter south (about 12 km) is Schmidt, around 40 km northwest is the crater Dionysius, and to the north-northeast are Manners (about 60 km) and Arago. This crater is roughly circular but with an irregular outer rim. The inner walls have slumped down towards the floor. The interior is irregular with several low ridges. To the northwest of Ritter is a system of parallel rilles designated Rimae Ritter. These follow a course to the northwest. Ray systems dominate around Ritter notably the west, they are founded inside the satellite crater Ritter B but not Ritter as the ray systems surrounds it.

Ranger 8 flew over Ritter prior to impact in Mare Tranquilitatis.

Both Sabine and Ritter were originally believed to be calderas rather than impact craters. In To A Rocky Moon, lunar geologist Don E. Wilhelms summarized: "They are identical twins in morphology and size (29-30 km). They lack radial rim ejecta and secondary craters despite their apparent youth. They are positioned at the presumably active edge of a mare. They are even aligned along graben, the Hypatia rilles. Most significant, they lack deep floors recognized since the days of Gilbert as diagnostic of impacts." However, after the Apollo landings were complete, it was realized that "all craters inside basins suffer enhanced isostatic uplift," because "the thin crust and greater heat inside basins lower the viscosity of the craters' substrate, allowing it to reach isostasy with its surroundings more quickly than can other craters."[1]

Oblique view from the south from Apollo 16

Satellite craters[edit]

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Ritter. All of its craters are located to the north, inbetweeen is Ritter B, between the main crater and that is Ritter C and further north is Ritter D.

Ritter Latitude Longitude Diameter
B 3.3° N 18.9° E 14 km
C 2.8° N 18.9° E 14 km
D 3.7° N 18.8° E 7 km


  1. ^ To a Rocky Moon: A Geologist's History of Lunar Exploration. Don E. Wilhelms, University of Arizona Press (1993). ISBN 978-0816510658

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