Janssen is an ancient

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

located in the highland region near the southeastern

lunar Lunar most commonly means "of or relating to the Moon". Lunar may also refer to: Arts and entertainment * ''Lunar'' (series), a series of video games * "Lunar" (song), by David Guetta * "Lunar", a song by Priestess from the 2009 album ''Prior t ...

limb Limb may refer to: Science and technology *Limb (anatomy), an appendage of a human or animal *Limb, a large or main branch of a tree *Limb, in astronomy, the curved edge of the apparent disk of a celestial body, e.g. lunar limb *Limb, in botany, ...

. The entire structure has been heavily worn and is marked by many lesser crater impacts. The outer wall is breached in multiple locations, but the outline of the crater rim can still be observed. The wall forms a distinctive

hexagon In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...

al shape upon the rugged lunar surface, with a slight curvature at the vertices. Janssen satellite craters map

The crater is named after French astronomer

Pierre Jules César Janssen Pierre Jules César Janssen (22 February 1824 – 23 December 1907), usually known as Jules Janssen, was a French astronomer who, along with English scientist Joseph Norman Lockyer, is credited with discovering the gaseous nature of the solar ...

. The prominent crater Fabricius lies entirely within the outer wall, in the northeast quadrant of the floor. A number of other lesser, but still notable craters mark the crater floor. Connected to the northeast rim is

Metius Adriaan Adriaanszoon, called Metius, (9 December 1571 – 6 September 1635), was a Dutch geometer and astronomer born in Alkmaar. The name "Metius" comes from the Dutch word ''meten'' ("measuring"), and therefore means something like "measurer" o ...

, and to the north is the heavily worn Brenner. Southeast of Janssen are the co-joined craters Steinheil and

Watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...

. Astride the southwest wall is the smaller Lockyer. Further to the east, although appearing nearby due to elongation, is the huge

Vallis Rheita Vallis Rheita is a linear valley on the near side of the Moon. It is located in the southeastern quadrant, and is oriented radially to Mare Nectaris. This valley appears to share a common origin with the Vallis Snellius to the northeast, as both ...

. In the southern two-thirds of Janssen can be discerned the remains of a large, concentric crater, the wall of which is overlaid by Fabricius. The floor of this inner depression contains a

rille Rille (German for 'groove') is typically used to describe any of the long, narrow depressions in the surface of the Moon that resemble channels. The Latin term is ''rima'', plural ''rimae''. Typically, a rille can be several kilometers wi ...

system named the Rimae Janssen. The rille curves from the rim of Fabricius to the southeast of the outer wall of Janssen, extending for a distance of up to 140 kilometers.

Satellite craters

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Janssen.

References

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External links

* {{Commons category Impact craters on the Moon