Mosaic of Lunar Orbiter 4 images
(spots in lower left are blemishes on original)
|Colongitude||343° at sunrise|
Posidonius is a lunar impact crater that is located on the north-eastern edge of Mare Serenitatis, to the south of Lacus Somniorum. The crater Chacornac is attached to the southeast rim, and to the north is Daniell.
The rim of Posidonius is shallow and obscured, especially on the western edge, and the interior has been overlain by a lava flow in the past. The crater ramparts can still be observed to the south and east of the crater rim, and to a lesser degree to the north.
There is a smaller, semi-circular rim of a concentric, flooded crater within the main rim, offset towards the eastern edge. There is no central peak, but the floor is hilly and laced with a rille system named the Rimae Posidonius. The floor is also slightly bulged due to the past lava uplift, which also likely produced the complex of rilles. The northeast rim is interrupted by the smaller crater Posidonius B. Within the crater rim, offset just to the west of center is another smaller crater Posidonius A.
On the Mare Serenitatis surface near Posidonius is a notable system of wrinkle ridges that parallel the nearby shore. These are designated the Dorsa Smirnov. At the peak of these ridges is a small craterlet with a diameter of 2 km. This craterlet is surrounded by a patch of high-albedo material, and is an example of a lunar bright spot. This peak was formerly designated Posidonius Gamma (γ).
The crater is named after Posidonius, a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher. It was given its name by Giovanni Riccioli as Possidonius, whose 1651 nomenclature system has become standardized. Earlier lunar cartographers had given the feature different names. Michael van Langren's 1645 map calls it "Lasaillii". And Johannes Hevelius called it "Insula Macra" of the ancient world.
By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Posidonius.
|A||31.7° N||29.5° E||11 km|
|B||33.1° N||30.9° E||14 km|
|C||31.1° N||29.6° E||2 km|
|E||30.5° N||19.7° E||3 km|
|F||32.8° N||27.1° E||6 km|
|G||34.8° N||27.2° E||5 km|
|J||33.8° N||30.7° E||22 km|
|M||34.3° N||30.0° E||10 km|
|N||29.7° N||21.0° E||6 km|
|P||33.6° N||27.5° E||15 km|
|W||31.6° N||20.1° E||3 km|
|Y||30.0° N||24.9° E||2 km|
|Z||30.7° N||22.9° E||6 km|
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