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| Coordinates | 1°36′N1°00′E / 1.6°N 1.0°E /1.6; 1.0 |
|---|---|
| Diameter | 287 km (178 mi) |
| Eponym | Bay of the Center |
Sinus Medii[1]/ˈsaɪnəsˈmiːdiaɪ/ (Latinsinus mediī "Middle Bay") is a smalllunar mare. It takes its name from its location at the intersection of theMoon'sequator andprime meridian; as seen from theEarth, 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 tolibration.
During theApollo 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 sentApollo 11 to Sinus Medii instead of ALS2,Mare Tranquillitatis (where it actually landed); another two-day delay would have resulted in ALS5, a site inOceanus Procellarum, being targeted.
The selenographiccoordinates of Sinus Medii are1°36′N1°00′E / 1.6°N 1.0°E /1.6; 1.0, and its diameter is 287 km.[1] It joinsMare Insularum in the west withMare Vaporum to the north.
The eastern part of this area is notable for a series ofrille systems. In the far northeast is the Rima Hyginus, which is bisected by the craterHyginus. At the far eastern end is the 220-km longRima Ariadaeus rille which continues eastward to the edge of theMare Tranquillitatis. At longitudes 4-6° E is the Rimae Triesnecker rille system, named after the craterTriesnecker just to the west.[2]
The northern edge of the Sinus Medii is formed by a highland region, with the impact cratersMurchison andPallas along the border. Near the northern border on this mare is the cup-shapedChladni.[2]
Another highland region lies to the south and southeastern edge of the Sinus Medii. Several flooded craters lie along this border, withFlammarion near the western edge, thenOppolzer,Réaumur, andSeeliger further east. TheRima Flammarion andRima Oppolzerrilles lie along the edge of the mare near their corresponding craters. Also along the southeast border and bisecting the prime meridian is the craterRhaeticus.
In the western half of the interior are the small cratersBruce andBlagg. Near the western end of the mare are the flooded cratersSchröter andSömmering.
The English astronomerWilliam Gilbert was the first to give a name to this mare, calling it Insula Medilunaria ("Middlemoon Island").[3] The idea for its present name originates withMichael van Langren, who labelled it Sinus Medius in his 1645 map.[4]Johannes Hevelius called the feature Mare Adriaticum ("TheAdriatic Sea") in his 1647 map.[5][6]Giovanni Riccioli called it Sinus Aestuum ("Bay of Hot Days") in his 1651 map.[7][8]
TheSurveyor 6 mission landed to the west-southwest ofBruce crater inside Sinus Medii in November 1967. Prior to that in July 1967, theSurveyor 4 had crashed nearby.
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