MoonBy : Valerie Chervinskaya 4-D

The Moon

The Moon (Latin: Luna) is the Earth's only natural satellite.[e][f][8] Although not the largest natural satellite in the Solar System, it is the largest relative to the size of the object it orbits (its primary) [g] and, after Jupiter's satellite Io, it is the second most dense satellite among those whose densities are known.

The Moon is in synchronous rotation with Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the most luminous object in the sky after the Sun. Although it appears a very bright white, its surface is actually dark, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art, and mythology. The Moon's gravitational influence produces the ocean tides and the slight lengthening of the day. The Moon's current orbital distance is about thirty times the diameter of Earth, causing it to have an apparent size in the sky almost the same as that of the Sun. This allows the Moon to cover the Sun nearly precisely in total solar eclipse. This matching of apparent visual size is a coincidence. The Moon's linear distance from Earth is currently increasing at a rate of 3.82±0.07 cm per year, but this rate is not constant.[9]

Internal structure

The Moon is a differentiated body: it has a geochemically distinct crust, mantle, and core. The Moon has a solid iron-rich inner core with a radius of 240 kilometers and a fluid outer core primarily made of liquid iron with a radius of roughly 300 kilometers. Around the core is a partially molten boundary layer with a radius of about 500 kilometers.[36] This structure is thought to have developed through the fractional crystallization of a global magma ocean shortly after the Moon's formation 4.5 billion years ago.[37] Crystallization of this magma ocean would have created a mafic mantle from the precipitation and sinking of the minerals olivine, clinopyroxene, and orthopyroxene; after about three-quarters of the magma ocean had crystallised, lower-density plagioclase minerals could form and float into a crust on top.[38] The final liquids to crystallise would have been initially sandwiched between the crust and mantle, with a high abundance of incompatible and heat-producing elements.[1] Consistent with this, geochemical mapping from orbit shows the crust is mostly anorthosite,[7] and moon rock samples of the flood lavas erupted on the surface from partial melting in the mantle confirm the mafic mantle composition, which is more iron rich than that of Earth.[1] Geophysical techniques suggest that the crust is on average ~50 km thick.[1]

Orbital characteristics

Average distance from Earth: 238,855 miles (384,400 km)

Perigee (closest approach to Earth): 225,700 miles (363,300 km)

Apogee (farthest distance from Earth): 252,000 miles (405,500 km)

Apollo Mission

As the time approached for the Apollo 16 Lunar Module to descend from lunar orbit to the Moon’s surface, Ken Mattingly, the Command Service Module pilot, found that the backup gimbals (mechanical devices that allow rotation in multiple axes) in the Command Service Module were faulty. These gimbals controlled the direction that the Command Service Module rockets fired, and without them, the crew would be forced to use the Lunar Module engines to return to Earth. Mission rules dictated that, in this scenario, the lunar landing would be canceled. However, after six long hours of troubleshooting and analysis by engineers in Houston, Mission Control made the call that the margins for safety were just barely adequate and they gave Apollo 16 the “Go” for lunar landing.

On April 21, 1972, exploration of the lunar surface continued as Apollo 16 touched down in the Descartes highlands. Unlike previous landing sites, which had contained clues about the historical period during which the maria (the dark, lava filled plains on the Moon’s surface) had formed, Descartes was chosen as a site to study the origins of the lunar highlands.

Of the potential sites in the lunar highlands that had been considered, Descartes was chosen because it appeared to be the an area with much volcanic activity. There was consensus among geologists at the time that the landing site contained typical examples of viscous lava flows that had piled up to create the hilly formations in the area, and some scientists had even gone so far as to chart various flow fronts and cinder cones. Accordingly, Charles Duke and John Young had been thoroughly trained in terrestrial volcanic analogs. Therefore, it was quite a shock when, soon after Apollo 16 landed, Duke and Young reported that they could see no evidence of volcanic rocks at the landing site.

Duke and Young were able to build on the experience of prior Apollo astronauts to help them complete the longest lunar extravehicular activity (EVA) period yet. With the help of the Lunar Roving Vehicle, the astronauts covered several kilometers of highland territory and brought back the second-largest collection of samples of all the missions, including the largest rock taken from the Moon.

Atmosphere of the moon

The moon has a very thin atmosphere, so a layer of dust — or a footprint — can sit undisturbed for centuries. And without much of an atmosphere, heat is not held near the planet, so temperatures vary wildly. Daytime temperatures on the sunny side of the moon reach 273 degrees F (134 C); on the dark side it gets as cold as minus 243 F (minus 153 C).

The moon's gravity

The moon's gravity pulls at the Earth, causing predictable rises and falls in sea levels known as tides. To a much smaller extent, tides also occur in lakes, the atmosphere, and within the Earth's crust.

As the Earth and moon orbit the sun together, the moon goes through several ‘phases.’ SPACE.com explains the 8 major named phases of the moon.

High tides are when water bulges upward, and low tides are when water drops down. High tide results on the side of the Earth nearest the moon due to gravity, and it also happens on the side farthest from the moon due to the inertia of water. Low tides occur between these two humps.