http://www.c3.lanl.gov/~cjhamil/SolarSystem/moon.html (Einblicke ins Internet, 10/1995)
The Moon
On July 20, 1969, Neil Armstrong became the first man to step onto the surface of the Moon. He was followed by Edwin Aldrin, both of the Apollo 11 mission. An experience on the Moon includes the effects of no atmosphere. With the exception of radio communications, sound cannot be heard since it travels through the medium of air and the sky is always black since diffraction of light does not occur without an atmosphere. Because of gravitational differences, a man weighing 180 pounds on Earth weighs only 30 pounds on the Moon.
The Moon is 384,403 km (238,857 miles) distant from the Earth. Its diameter is 3,476 km (2,160 miles). Both the rotation of the Moon and its revolution around Earth takes 27 days, 7 hours, and 43 minutes. This synchronous rotation is caused by an unsymmetrical distribution of mass in the Moon which has allowed Earth's gravity to keep one lunar hemisphere permanently turned toward Earth. Optical liberations have been observed telescopically since the mid-seventeenth century and very small but real liberations (maximum about O°.O4) are caused by the effect of the Sun's gravity and the eccentricity of Earth's orbit, perturbing the Moon's orbit and allowing cyclical preponderances of torque in both east-west and north-south directions.
Four nuclear powered seismic stations were installed during the Apollo project to collect seismic data about the interior of the Moon. There is only residual tectonic activity due to cooling and tidal forcing, but other moonquakes have been caused by meteor impacts and artificial means. The results have shown the Moon to have a crust 60 km thick at the center of the near side. If this crust is uniform over the Moon, it would constitute about 10% of the Moon's volume as compared to the less than 1% crust on Earth. The seismic determinations of a crust and mantle on the Moon indicate a layered planet with differentiation by igneous processes. There is no evidence for an iron-rich core unless it were a small one. Seismic information has influenced theories about the formation and evolution of the Moon.
The Moon was heavily bombarded early in its history which caused many of the original rocks of the ancient crust to be thoroughly mixed, melted, buried, or obliterated, thus reseting isotopic clocks. Meteoritic impacts brought a variety of "exotic" rocks to the Moon from different areas so that samples obtained from only 9 Moon locations produced many different rock types available for study. The impacts also exposed Moon rocks of great depth and distributed their fragments laterally away from their places of origin making them more accessible. The underlying crust was also thinned and cracked, allowing molten basalt from the interior to reach the surface. Because the Moon has no atmosphere nor water, the components in the soils do not weather chemically as they would on Earth. Rocks more than 4 billion years old still exist there yielding information about the early history of the solar system that is unavailable on Earth. Geological activity on the Moon consists of occasional large impacts and the continued formation of the regolith. It is thus considered geologically dead. With such an active early history of bombardment and a relatively abrupt end of heavy impact activity, the Moon is considered fossilized in time.
The Apollo and Luna missions returned 382 kg of rock and soil from which three major surface materials have been studied: the regolith, the maria, and the terrae. Micrometeorite bombardment has thoroughly pulverized the surface rocks into a fine-grained debris called the regolith. The regolith, or lunar soil, is unconsolidated mineral grains, rock fragments, and combinations of these which have been welded by impact-generated glass. It is found over the entire Moon, with the exception of steep crater and valley walls. It is 2 to 8 meters thick on the maria and may exceed 15 meters on the terrae, depending on how long the bedrock underneath it has been exposed to meteoritic bombardment.
The dark, relatively lightly cratered maria cover about 16% of the lunar surface and is concentrated on the nearside of the Moon, mostly within impact basins. This concentration may be explained by the fact that the Moon's center of mass is offset from its geometric center by about 2 km in the direction of Earth, probably because the crust is thicker on the farside. It is possible, therefore, that basalt magmas rising from the interior reached the surface easily on the nearside, but encountered difficulty on the farside. Mare rocks are basalt and most date from 3.8 to 3.1 billion years. Some fragments in highland breccias date to 4.3 billion years and high resolution photographs suggest some mare flows actually embay young craters and may thus be as young as 1 billion years. The maria average only a few hundred meters in thickness but are so massive they frequently deformed the crust underneath them which created fault-like depressions and raised ridges.
The relatively bright, heavily cratered highlands are called terrae. The craters and basins in the highlands are formed by meteorite impact and are thus older than the maria, having accumulated more craters. The dominant rock type in this region contain high contents of plagioclase feldspar (a mineral rich in calcium and aluminum) and are a mixture of crustal fragments brecciated by meteorite impacts. Most terrae breccias are composed of still older breccia fragments. Other terrae samples are fine-grained crystalline rocks formed by shock melting due to the high pressures of an impact event. Nearly all of the highland breccias and impact melts formed about 4.0 to 3.8 billion years ago. The intense bombardment began 4.6 billion years ago, which is the estimated time of the Moon's origin.
Mass (kg) ......................................... 7.349e+22 Mass (Earth = 1) ................................. 1.2298e-02 Equatorial radius (km) .............................. 1,737.4 Equatorial radius (Earth = 1) .................... 2.7241e-01 Mean density (gm/cm^3) ................................. 3.34 Mean distance from Earth (km) ....................... 384,400 Rotational period (days) ........................... 27.32166 Orbital period (days) .............................. 27.32166 Mean orbital velocity (km/sec) ......................... 1.03 Orbital eccentricity ................................... 0.05 Tilt of axis ........................................... 6.68° Orbital inclination ............................... 18.3-28.6° Equatorial surface gravity (m/sec^2) ................... 1.62 Equatorial escape velocity (km/sec) .................... 2.38 Visual geometric albedo ................................ 0.12 Magnitude (Vo) ....................................... -12.74 Mean surface temperature (day) ......................... 107°C Mean surface temperature (night) ...................... -153°C Maximum surface temperature ........................... 123°C Minimum surface temperature .......................... -233°C
Moon Animations
The following is a collection of images showing the moon.
Apollo 17 - Whole Moon View
(GIF, 222K;
GIF, 3M)
This full disc of the Moon was photographed by the Apollo 17 crew during
their trans-Earth coast homeward following a successful lunar landing
mission in December 1972. Mare seen on this photo include Serentatis,
Tranquillitatis, Nectaris, Foecunditatis and Crisium.
(Courtesy NASA).
Far Side of the Moon
(GIF, 342K;
TIF, 2M)
This image was taken by Apollo 11 astronauts in 1969. It shows a portion
of the Moon's heavily cratered far side. The large crater is
approximately 80 km ( 50 miles ) in diameter.
The rugged terrain seen here is typical of the farside of the Moon.
(Courtesy NASA).
Lunar South Pole
(GIF, 193K;
TIF, 4M;
caption)
This mosaic is composed of 1500 Clementine images
of the south polar region of the Moon.
The top half of the mosaic
faces Earth. Clementine has revealed what appears to be a major
depression near the lunar south pole (center), evident from the presence
of extensive shadows around the pole. This depression probably is an
ancient basin formed by the impact of an asteroid or comet. A
significant portion of the dark area near the pole may be in permanent
shadow, and sufficiently cold to trap water of cometary origin in the
form of ice.
The impact basin Schrodinger (near the 4 o'clock position) is a two-ring basin, about 320 km in diameter which is recognized to be the second youngest impact basin on the Moon. The center of Schrodinger is flooded by lavas. A volcanic vent seen in the floor of Schrodinger is one of the largest single explosive volcanoes on the Moon. (Courtesy DSPSE/NASA).
Apollo 11
(GIF, 117K)
The Apollo 11 Lunar Module ascent stage, with Astronauts Neil A. Armstrong
and Edwin E. Aldrin Jr. aboard, is photographed from the Command and
Service Modules (CSM) during rendezvous in lunar orbit. The Lunar Module
(LM) was making its docking approach to the CSM. Astronaut Michael Collins
remained with the CSM in lunar orbit while the other two crewmen explored
the lunar surface. The large, dark-colored area in the background is
Smyth's Sea, centered at 85 degrees east longitude and 2 degrees south
latitude on the lunar surface (nearside). This view looks west. The Earth
rises above the lunar horizon. (Courtesy NASA).
Apollo 11 - Flag
(GIF, 223K;
TIF, 2M)
Astronaut Edwin E. Aldrin Jr., lunar module pilot, poses for a photograph
beside the deployed United States flag during Apollo 11 extravehicular
activity on the lunar surface. The Lunar Module "Eagle" is on the left. The
footprints of the astronauts are clearly visible in the soil of the Moon.
This picture was taken by Astronaut Neil A. Armstrong, commander, with a
70mm lunar surface camera. (Courtesy NASA).
Apollo 11 - Earth from the Moon
(GIF, 277K;
TIF, 2M)
This view of the Earth rising over the Moon's horizon was taken from the
Apollo 11 spacecraft. The lunar terrain pictured is in the area of Smuth's
Sea on the nearside. (Courtesy NASA).
Apollo 11 - Footprint on the Moon
(GIF, 414K;
GIF, 1M)
A close-up view of an astronaut's footprint in the lunar soil, photographed
with a 70mm lunar surface camera during the Apollo 11 extravehicular
activity (EVA) on the Moon.
Apollo 15 - Lunar Roving Vehicle
(GIF, 272K;
TIF, 8M)
This is a view of the Lunar Roving Vehicle photographed alone against
the desolate lunar background during an Apollo 15 lunar surface
extravehicular activity (EVA) at the Hadley-Apennine landing site. This
view is looking north. The west edge of Mount Hadley is at the upper right
edge of the picture. Mount Hadley rises approximately 4,500 meters above
the plain. The most distant lunar feature visible is approximately 25
kilometers away.
Apollo 17 - Taurus-Littrow Landing Site
(GIF, 291K;
TIF, 2M)
This is the landing site of the last Apollo mission (Apollo 17). It was in
the valley among the Taurus-Littrow hills on the southeastern rim of
Mare Serenitatis. Two of the Apollo 17 astronauts explored the
valley with the aid of an electrically powered car. This image
shows Harrison H. Schmitt inspecting a huge boulder that has
rolled down the side of an adjacent hill.
Apollo 17 - Large Lunar Boulder
(GIF, 191K;
TIF, 2M)
Earth in the far distant background is seen above a large lunar boulder
on the Moon. This photo was taken with a handheld Hasselblad camera by the
last two Moon walkers in the Apollo Program.
Apollo 17 - Lunar Scape
(GIF, 310K;
TIF, 2M)
This image is an excellent view of the desolate lunar space at Station 4
showing scientist-astronaut Harrison H. Schmitt, lunar module pilot,
working at the Lunar Roving Vehicle during the second Apollo 17 extravehicular
activity at the Taurus-Littrow landing site. This is the area where Schmitt
first spotted the orange soil which is visible on either side of the Lunar
Roving Vehicle in this picture. Shorty Crater is to the right, and the peak
in the center background is Family Mountain. A portion of South Massif is
on the horizon at the left edge.
Apollo 17 - Orange Soil
(GIF, 199K;
TIF, 3M)
These orange glass spheres and fragments are the finest particles ever brought
back from the Moon. The partiles range in size from 20 to 45 microns. The
orange soil was brought back from the Taurus-Littrow landing site by the
apollo 17 crewmen. Scientist-Astronaut Harrison J. Schmitt discovered the
orange soil at Shorty Crater. The orange particles, which are intermixed
with black and black-speckled grains, are about the same size as the
particles that compose silt on Earth. Chemical analysis of the orange soil
material has show the sample to be similar to some of the samples brought
back from the Apollo 11 (Sea of Tranquility) site several hundred miles to
the southwest. Like those samples, it is rich in titanium (8%) and iron
oxide (22%). But unlike the Apollo 11 samples, the orange soil is
unexplainably rich in zinc. The orange soil is probably of volcanic origin
and not the product of meteorite impact.
Apollo 17 - Oblique view of Copernicus
(GIF, 226K;
GIF, 777K)
This is an oblique view of the large crater Copernicus on the lunar
nearside, as phtographed from the Apollo 17 spacecraft in lunar orbit.
Earth
