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(Freely adapted from Wikipedia)
Triesnecker is a prominent lunar impact crater (dia. 26 Km, dept. 2.8 Km) that is located in the Sinus Medii, near the central part of the Moon's near side.
The crater rim of Triesnecker is somewhat distorted from a circular shape, having a notable bulge in the western wall, and lesser rises in the southeastern and northeastern rims. The inner walls are terraced and the interior is somewhat rough, with a central peak at the midpoint. Triesnecker has a ray system that is most prominent when the sun is at a high angle. The rays extend over 300 kilometers.
To the east of this crater is an extensive system of rilles extending over an area 200 kilometers across, running generally north–south. These were likely created by tectonic forces beneath the surface. Beyond, to the northeast, is the Rima Hyginus valley, with the crater Hyginus at the midpoint.
SinusMedii ("Central 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.
The eastern part of this area is notable for a series of rille systems. In the far northeast is the Rima Hyginus, which is bisected by the crater Hyginus. At the far eastern end is the 220-km long Rima Ariadaeus rille which continues eastward to the edge of the Mare Tranquillitatis. Crossing the prime meridian longitude is the Rimae Triesnecker rille system, named after the crater Triesnecker just to the west.
Hyginus is a small lunar caldera located at the east end of the Sinus Medii. Its rim is split by a long, linear rille Rima Hyginus that branches to the northwest and to the east-southeast for a total length of 220 kilometers. The crater is deeper than the rille, and lies at the bend where they intersect. Together the crater Hyginus and Rima Hyginus form a distinctive and prominent feature in an otherwise flat surface. Smaller craterlets can also be discerned along the length of this rille, possibly caused by a collapse of an underlying structure.
Hyginus is one of the few craters on the Moon that was not created as a result of an impact, and is instead believed to be volcanic in origin. It lacks the raised outer rim that is typical with impact craters.
It was also the planned site for the canceled Apollo 19 mission.
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