 Lunar Orbiter 4 image centered on Gerard. Gerard A is the smaller crater at left. | |
| Coordinates | 44°30′N80°00′W / 44.5°N 80.0°W Coordinates: 44°30′N80°00′W / 44.5°N 80.0°W |
|---|---|
| Diameter | 98.78 km |
| Depth | 2.2 km |
| Colongitude | 82° at sunrise |
| Eponym | Alexander Gerard |
Gerard is a lunar impact crater that lies along the western edge of the Oceanus Procellarum near the northwest limb of the Moon's near side. It is located to the north-northwest of the crater von Braun, and northeast of Bunsen. Because of its location, Gerard appears strongly foreshortened when viewed from the Earth, hindering observation.
Lunar craters are impact craters on Earth's Moon. The Moon's surface has many craters, almost all of which were formed by impacts.
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.
Oceanus Procellarum is a vast lunar mare on the western edge of the near side of the Moon. It is the only one of the lunar maria to be called an "Oceanus" (ocean), due to its size: Oceanus Procellarum is the largest of the maria, stretching more than 2,500 km (1,600 mi) across its north-south axis and covering roughly 4,000,000 km2 (1,500,000 sq mi), accounting for roughly 10.5% of the total lunar surface area.
This is a worn and eroded formation with a rim that has been nearly obliterated in some locations and distorted in others. The northern half of the rim has outward bulges to the northeast, north, and northwest. The interior floor is rough in places, with several small and tiny craters along the floor and the eastern rim.
To the northwest of this formation is the unusual Gerard Q Inner (eastern floor covered in dark-hued basaltic lava) within the larger Gerard Q Outer, and a system of rilles named the Rimae Gerard. These extend for a distance of about 100 kilometers.
Hue is one of the main properties of a color, defined technically, as "the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, blue, and yellow",. Hue can typically be represented quantitatively by a single number, often corresponding to an angular position around a central or neutral point or axis on a colorspace coordinate diagram or color wheel, or by its dominant wavelength or that of its complementary color. The other color appearance parameters are colorfulness, saturation, lightness, and brightness.
Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt. Basalt lava has a low viscosity, due to its low silica content, resulting in rapid lava flows that can spread over great areas before cooling and solidification. Flood basalt describes the formation in a series of lava basalt flows.
Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption, usually at temperatures from 700 to 1,200 °C. The structures resulting from subsequent solidification and cooling are also sometimes described as lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites, though such material located below the crust is referred to by other terms.
