Helmert (crater)
Encyclopedia
Helmert is a lunar
crater
at the southern edge of the Mare Smythii
. It lies near the eastern limb of the Moon
, and from the Earth
it is seen nearly from the side. The visibility of this feature can be strongly affected by libration
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
, leaving a level surface across the bottom of both craters. This floor is nearly featureless, and has the same low albedo
as the dark lunar mare
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.
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...
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...
at the southern edge of the Mare Smythii
Mare Smythii
Mare Smythii is a lunar mare located along the equator on the easternmost edge of the lunar near side. The Smythii basin where the mare is located is of the Pre-Nectarian epoch, while the surrounding features are of the Nectarian system...
. It lies near the eastern limb of 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...
, and from the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
it is seen nearly from the side. The visibility of this feature can be strongly affected by libration
Libration
In astronomy, libration is an oscillating motion of orbiting bodies relative to each other, notably including the motion of the Moon relative to Earth, or of Trojan asteroids relative to planets.-Lunar libration:...
of the Moon in its orbit.
This crater forms part of a merged pair with the similar crater Kao
Kao (crater)
Kao is a small lunar crater that is located near the eastern limb of the Moon. It lies near the southern edge of the Mare Smythii, a lunar mare that continues onto the far side of the surface. This crater lies to the east-southeast of the crater Widmannstätten...
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
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
, leaving a level surface across the bottom of both craters. This floor is nearly featureless, and has the same low 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...
as the dark lunar 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...
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.