Reiner Gamma is an albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 feature that is located on the Oceanus Procellarum

Oceanus Procellarum

Oceanus Procellarum is a vast lunar mare on the western edge of the near side of the Earth's Moon. Its name derives from the old superstition that its appearance during the second quarter heralded bad weather...

, to the west of the crater Reiner

Reiner (crater)

Reiner is a lunar impact crater on the Oceanus Procellarum, in the western part of the Moon. It has a nearly circular rim, but appears oval in shape due to foreshortening. The rim edge is well-defined and has not been eroded by impacts. In the mid-point of the irregular crater floor is a central peak...

 on the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. The center of the formation is located at selenographic coordinates . It has an overall dimension of about 70 kilometres. The feature has a higher albedo than the relatively dark mare

Lunar mare

The lunar maria are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions. They were dubbed maria, Latin for "seas", by early astronomers who mistook them for actual seas. They are less reflective than the "highlands" as a result of their iron-rich compositions, and...

 surface, with a diffuse appearance and a distinctive swirling, concentric oval shape. Related albedo features continue across the surface to the east and southwest, forming loop-like patterns over the mare.

Reiner Gamma is not associated with any particular irregularities in the surface, and so the cause was a mystery until similar features were discovered in Mare Ingenii

Mare Ingenii

Mare Ingenii is one of the few lunar mare features on the far side of the Moon. The mare sits in the Ingenii basin. This basin material is of the Pre-Nectarian epoch. The mare material located in Ingenii and the surrounding craters is of the Upper Imbrian epoch...

 and Mare Marginis

Mare Marginis

Mare Marginis is a lunar mare that lies on the very edge of the lunar nearside. The selenographic coordinates of this feature are 13.3° N, 86.1° E, and the diameter is 420 km. The name is Latin for "Sea of the Edge"....

 on photographs taken by orbiting spacecraft. The feature on Mare Ingenii is located at the lunar opposite point from the center of Mare Imbrium

Mare Imbrium

Mare Imbrium, Latin for "Sea of Showers" or "Sea of Rains", is a vast lunar mare filling a basin on Earth's Moon and one of the larger craters in the Solar System. Mare Imbrium was created when lava flooded the giant crater formed when a very large object hit the Moon long ago...

. Likewise the feature on Mare Marginis is opposite the mid-point of Mare Orientale

Mare Orientale

Mare Orientale is one of the most striking large scale lunar features, resembling a target ring bull's-eye. Located on the extreme western edge of the lunar nearside, this impact basin is difficult to see from an Earthbound perspective.Material from this basin was not sampled by the Apollo program...

. Thus it is believed that the feature resulted from seismic energies generated by the impacts that created these maria. Unfortunately there is no such lunar mare formation located precisely on the opposite surface of the Moon, although the large crater Tsiolkovskiy

Tsiolkovskiy (crater)

Tsiolkovskiy is a large lunar impact crater that is located on the far side of the Moon. It lies in the southern hemisphere, to the west of the crater Gagarin, and northwest of Milne. Just to the south is Waterman, with Neujmin to the south-southwest. This feature was discovered on photographs sent...

 lies within one crater diameter.

The central feature of Reiner Gamma does bear a resemblance to the dipolar formation created by iron filings on a surface with a bar magnet

Magnet

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...

 on the underside. Low-orbiting spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 have observed a relatively strong magnetic field associated with each of these albedo markings. Some have speculated that this magnetic field and the patterns were created by comet

Comet

A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

ary impacts. However the true cause remains uncertain.

Reiner Gamma's magnetic field strength is approximately 15 nT, measured from an altitude of 28 km. This is one of the strongest localized magnetic anomalies on the Moon. The surface field strength of this feature is sufficient to form a mini-magnetosphere that spans 360 km at the surface, forming a 300 km thick region of enhanced plasma where the solar wind

Solar wind

The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

 flows around the field. As the particles in the solar wind are known to darken the lunar surface, the magnetic field at this site may account for the survival of this albedo feature.

In early lunar

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 map

Map

A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....

s by Francesco Grimaldi, this feature was incorrectly identified as a crater

Impact crater

In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

. His colleague Giovanni Riccioli then named it Galilaeus, after Galileo Galilei

Galileo Galilei

Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...

. The name was later transferred northwest to the current crater Galilaei

Galilaei (lunar crater)

Galilaei is a lunar impact crater located in the western Oceanus Procellarum. Some distance to the southeast is the crater Reiner, while to the south-southwest is Cavalerius. Northeast of the crater is a meandering rille named the Rima Galilaei...

.

Other references

• Ewen A. Whitaker, Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature, Cambridge University Press, 1999
  1999 in literature
  The year 1999 in literature involved some significant events and new books.-Events:*June 19 - Stephen King is hit by a Dodge van while taking a walk. He spends the next three weeks hospitalized...
  
  , ISBN 0-521-62248-4.