Firmicus (crater)

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Firmicus
Firmicus Crater AS17-M-2223.jpg
The Firmicus crater as seen from the Apollo 17 CSM
Coordinates 7°18′N 63°24′E / 7.3°N 63.4°E / 7.3; 63.4Coordinates: 7°18′N 63°24′E / 7.3°N 63.4°E / 7.3; 63.4
Diameter 56 km
Depth 1.5 km
Colongitude 297° at sunrise
Eponym Firmicus Maternus

Firmicus is a lunar impact crater that lies in the eastern part of the Moon's near side, so that from Earth it appears oval in shape due to foreshortening. It is, however, very nearly circular. The crater is located to the west of the Mare Undarum, and northeast of the similar-sized crater Apollonius. To the north of Firmicus are the craters van Albada and Auzout. Attached to its northwest rim is the Lacus Perseverantiae, a miniature lunar mare.

The crater is named after Julius Firmicus Maternus.

The most notable aspect of Firmicus is the dark, flat floor. It has a similar albedo to the surface of Mare Crisium to the north, making it stand out somewhat from its surroundings. The floor has suffered no significant impacts since it was created, although there are undoubtedly many minor impacts across its surface. The outer rim of Firmicus has undergone some erosion, particularly along the northern rim where it is overlain by a pair of small craterlets.

From that location the Earth would appear in the lunar sky at over 26 degrees from the top towards the west and 7 degrees to the left.

Satellite craters[edit]

Firmicus crater and its satellite craters taken from Earth in 2012 at the University of Hertfordshire's Bayfordbury Observatory with the telescopes Meade LX200 14" and Lumenera Skynyx 2-1

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Firmicus. Firmicus A is in the southeast, Firmicus B and C are to the east with the latter being concentric, Firmicus D are to the south-southeast, Firmicus E is a small crater to the north that adjoins the main crater, Firmicus F and G are nearly to the west-southwest, Firmicus H is further west in the nearby lunar lake and Firmicus M is further south.

Oblique view from Apollo 10, with Firmicus in the background and Mare Undarum in the foreground
Oblique view of Firmicus facing south from Apollo 17
Firmicus Latitude Longitude Diameter
A 6.4° N 65.1° E 8 km
B 7.3° N 65.8° E 14 km
C 7.7° N 66.5° E 13 km
D 5.9° N 64.4° E 11 km
E 8.0° N 63.6° E 9 km
F 6.5° N 61.8° E 9 km
G 6.9° N 61.9° E 9 km
H 7.5° N 60.3° E 7 km
M 4.1° N 67.2° E 42 km

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