Helmert is a

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 ...

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 craters ...

at the southern edge of the

Mare Smythii Mare Smythii (Latin for "Smyth's Sea") is a lunar mare located along the equator on the easternmost edge of the Moon's near side. It is named for the 19th-century British astronomer William Henry Smyth. The Smythii basin where the mare is located ...

. It lies near the eastern limb of 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 ...

, and from the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

it is seen nearly from the side. The visibility of this feature can be strongly affected by

libration In lunar astronomy, libration is the wagging or wavering of the Moon perceived by Earth-bound observers and caused by changes in their perspective. It permits an observer to see slightly different hemispheres of the surface at different tim ...

of the Moon in its orbit. This crater forms part of a merged pair with the similar crater Kao on its northern side. There is a gap in the rims where these two craters are joined, and the interior floors have been resurfaced by

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

, leaving a level surface across the bottom of both craters. This floor is nearly featureless, and has the same low

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

as the dark

lunar mare The lunar maria (; singular: mare ) are large, dark, basaltic plains on Earth's Moon, formed by ancient asteroid impacts on the far side on the Moon that triggered volcanic activity on the opposite (near) side. They were dubbed , Latin for 'seas' ...

to the north. The outer rim has a small crater joined to the eastern edge of the northern gap, but is otherwise not overlain by any notable craters. The crater's name was approved by the

IAU 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, outreach ...

in 1973.Helmert
Gazetteer of Planetary Nomenclature, International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN)

References

* * * * * * * * * * * * {{refend Impact craters on the Moon