Sinus Medii (Latin sinus mediī "Middle Bay") is a small lunar mare. It takes its name from its location at the intersection of the Moon's equator and prime meridian; as seen from the Earth, this feature is located in the central part of the Moon's near side, and it is the point closest to the Earth. From this spot, the Earth would always appear directly overhead, although the planet's position would vary slightly due to libration.

left|thumb|421x421px|Sinus Medii and closer craters with mineral postprocessing

During the Apollo program, Sinus Medii was designated Apollo Landing Site 3 (ALS3). Flight operations planners were concerned about having the optimum lighting conditions at the landing site. Hence, alternative landing sites moved progressively westward, following the terminator. A delay of two days for weather or equipment reasons would have sent Apollo 11 to Sinus Medii instead of ALS2, Mare Tranquillitatis (where it actually landed); another two-day delay would have resulted in ALS5, a site in Oceanus Procellarum, being targeted.

Geology

thumb|left|Oblique view facing south of central Sinus Medii from [[Lunar Orbiter 2, showing Bruce crater at right and Oppolzer crater above left]]

thumb|right|Oblique view facing north from [[Apollo 16]]

The selenographic coordinates of Sinus Medii are , and its diameter is 287 km.

The northern edge of the Sinus Medii is formed by a highland region, with the impact craters Murchison and Pallas along the border. Near the northern border on this mare is the cup-shaped Chladni. The idea for its present name originates with Michael van Langren, who labelled it Sinus Medius in his 1645 map. Johannes Hevelius called the feature Mare Adriaticum ("The Adriatic Sea") in his 1647 map. Giovanni Riccioli called it Sinus Aestuum ("Bay of Hot Days") in his 1651 map.

Exploration

thumb|left|Mosaic of the mare surface from Surveyor 6

The Surveyor 6 mission landed to the west-southwest of Bruce crater inside Sinus Medii in November 1967. Prior to that in July 1967, the Surveyor 4 had crashed nearby.

References

  • Sinus Medii at The Moon Wiki