Why Geminus appears oval from Earth

Feature Profile & Selenographic Data

Feature type

crater

Coordinates

34.42° N · 56.66° E

Diameter

81.98 km

IAU approval

1935/01/01 00:00:00

LAC quadrangle

LAC-27 · Geminus

Geological Period

Eratosthenian

Geological Chronicle

Near the Moon’s northeastern limb, Geminus looks oval because of foreshortening, though it is more nearly circular. The IAU named the crater in 1935 after a Greek astronomer.

Its rim has outward notches, especially to the north and east. Ejecta remains visible in the rough surroundings beyond it, while impact rays have long since worn away through space weathering. The wide, terraced inner wall is somewhat muted by impact erosion.

The floor has no notable impacts. A long, slender central ridge lies at its midpoint, alongside a pair of readily observed clefts. An infrared spectrum of pure crystalline plagioclase has been identified on the ridge and western floor.

Chronology & Exploration

1. Eratosthenian Formation period assigned

   The crater’s formation is dated to the Eratosthenian period of the lunar geologic timescale.

2. 1935 IAU names the crater

   The IAU named Geminus in 1935; the registry identifies its namesake as a Greek astronomer.

3. Undated Plagioclase spectrum identified

   An infrared spectrum of pure crystalline plagioclase was identified on the central rise and western floor.

Scientific Sources & References

• IAU Gazetteer of Planetary Nomenclature — Official feature registry for identity, coordinates, diameter, and name origin.
• Wikipedia: Geminus (crater) — Source for the crater’s apparent shape, geology, formation period, and spectral observation.

Name Origin

Greek astronomer (unkn-c. 70 B.C.).