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| Coordinates | 44°58′S40°49′E / 44.96°S 40.82°E Coordinates: 44°58′S40°49′E / 44.96°S 40.82°E |
|---|---|
| Diameter | 201 km |
| Depth | 2.9 km |
| Colongitude | 320° at sunrise |
| Eponym | Pierre J. C. Janssen |
Janssen is an ancient impact crater located in the highland region near the southeastern lunar limb. 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 hexagonal shape upon the rugged lunar surface, with a slight curvature at the vertices.
An impact crater is an approximately circular depression in the surface of a planet, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity impact of a smaller body. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Impact craters range from small, simple, bowl-shaped depressions to large, complex, multi-ringed impact basins. Meteor Crater is a well-known example of a small impact crater on Earth.
Earth's Moon is an astronomical body that orbits the planet and acts as its only permanent natural satellite. It is the fifth-largest satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits. The Moon is, after Jupiter's satellite Io, the second-densest satellite in the Solar System among those whose densities are known.
In geometry, a hexagon is a six-sided polygon or 6-gon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°.
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The crater is named after French astronomer Pierre Jules César Janssen. [1]
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, and to the north is the heavily worn Brenner. Southeast of Janssen are the co-joined craters Steinheil and Watt. Astride the southwest wall is the smaller Lockyer. Further to the east, although appearing nearby due to elongation, is the huge Vallis Rheita.
Fabricius is a lunar impact crater that is located within the northeast part of the walled plain Janssen. Attached to the north-northwest rim is the slightly larger cater Metius. Fabricius has multiple central peaks that rise to 0.8 km, with a rugged rise to the northwest running north–south. The rim is lumpy and somewhat distended, most noticeably to the southwest and south. It is 78 kilometers in diameter and 2,500 meters deep. It is from the Eratosthenian period, 3.2 to 1.1 billion years ago. It is named after David Fabricius, a 16th-century German astronomer.
A circular sector or circle sector, is the portion of a disk enclosed by two radii and an arc, where the smaller area is known as the minor sector and the larger being the major sector. In the diagram, θ is the central angle in radians, the radius of the circle, and is the arc length of the minor sector.
Metius is a lunar impact crater located in the rugged highlands to the southeast of the Moon's near side. To the southwest the rim is attached to the crater Fabricius. Offset to the west-northwest is the heavily worn crater Brenner. Further away to the northeast is the crater Rheita and the long gorge Vallis Rheita.
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 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.
Rille 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 up to several kilometers wide and hundreds of kilometers in length. However, the term has also been used loosely to describe similar structures on a number of planets in the Solar System, including Mars, Venus, and on a number of moons. All bear a structural resemblance to each other.
