Ghost crater, Rimae Secchi, Rima Messier (LRO)

Rimae Secchi is a system of

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 wid ...

s on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

, in northwestern

Mare Fecunditatis Mare Fecunditatis (Latin ''fēcunditātis'', the "Sea of Fecundity" or "Sea of Fertility") is a lunar mare in the eastern half of the visible Moon. The mare has a maximum diameter of 840 km. __NOTOC__ Description The Fecunditatis basin forme ...

. They are approximately 40 km long and run along the shore of the mare. Rimae Secchi are named after the nearby crater Secchi which, in turn, is named after an Italian astronomer

Angelo Secchi Angelo Secchi (; 28 June 1818 – 26 February 1878) was an Italian Catholic priest, astronomer from the Italian region of Emilia. He was director of the observatory at the Pontifical Gregorian University (then called the Roman College) for 28 y ...

. The name of the rilles was approved by the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

in 1985. In 1974, the name '' Fossae Secchi'' was proposed on a mapLunar Topographic Orthophotomap LTO-61C4 (Secchi)
published by the US Defense Mapping Agency, but this name was not adopted (on the Moon, the term ''Rima'' is traditionally used instead of ''Fossa''). Before this, during preparation to

Apollo 8 Apollo 8 (December 21–27, 1968) was the first crewed spacecraft to leave low Earth orbit and the first human spaceflight to reach the Moon. The crew orbited the Moon ten times without landing, and then departed safely back to Earth. These ...

and 10 flight, the rilles were informally nicknamed ''Apollo Rille''. The northern end of Rimae Secchi is Y-shaped, and the southern part consists of several separate troughs. Rimae Secchi run along the northwestern rim of a ghost crater (lava-filled crater) of approximately 85 km diameter. The rilles are centered at . The northern part of Rimae Secchi is surrounded with a dark halo, probably

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

deposits like

volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...

. Such deposits are common near the edges of lunar maria, including several areas in

. To see this feature, a telescope with an

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

of 20 cm or larger is needed.

References

External links

Map of the region
(Rimae Secchi are in lower right).
Lunar Topographic Orthophotomap LTO-61C4 (Secchi)
*
Photo by Apollo 10

Literature

* * {{DEFAULTSORT:Secchi Rimae Geological features on the Moon Mare Fecunditatis