A satellite {Moon} orbits Earth.
properties
Diameter is 2,000,000 meters. Mass is 1/80 of Earth mass. Surface area equals Africa area. Density is 2/3 of Earth density. Gravity is 1/5 of Earth gravity.
orbit
Orbit tilts at 5-degree incline to Earth orbit. Moon is 376,000,000 meters from Earth. Gravitational effect of Earth spin moves Moon slowly away from Earth. 4,000,000,000 years ago, Moon was 100,000,000 meters from Earth.
rotation
Moon rotates every 27.3 days, keeping same side toward Earth, ever since 10^9 years ago.
temperature
Surface temperature is 200 C by day and -150 C at night.
atmosphere
Moon has thin atmosphere with no water.
layers
Core has radius 400 miles and is molten. Peridotite and dunite lie from 400 miles from center to 40 miles below surface. Peridotite and dunite are oxide rocks like those in Earth mantle. Basalt layer lies from 40 to 15 miles deep. Crust is anorthositic rock 60,000 meters thick, with some granite.
surface
Surface has basalt rock from volcanoes that erupted more than 3,000,000,000 years ago, making mountains 8000 meters high. Mare basalt, from partial interior melting, is in plains {maria}. Another basalt type has anorthositic rock and KREEP norite from mountain {highland} partial melting. KREEP norite has potassium, rare earths, and phosphorus.
craters
Most craters are more than 4,000,000,000 years old. Largest crater is 250,000-meter diameter and 1000 meters high. Craters are 10 to 20 times bigger than their meteors.
history
Moon began when Mars-sized body collided with Earth and splashed material into orbit. It is much less likely that it began from smaller bodies in orbit around Earth or by capture. Orbiting material gravitated together and melted surface. Lighter molecules rose to surface and cooled to become crust. Later, before 4.2 x 10^9 years ago, meteorites pressed highland rocks together to make breccia. Then crust formed again. Then KREEP norite formed around Mare Imbrium. Then large impacts 4 x 10^9 years ago made maria basins. Then volcanoes erupted for 0.7 x 10^9 to 1.0 x 10^9 years, filling maria with lava. Finally, Moon cooled.
features
Tycho crater is at low center. Copernicus crater is at left center. Archimedes crater is at low center. Ptolemaeus crater is at center. Carpathian Mountains are around Copernicus. Mare Imbrium plain or Sea of Rains is at left and up. Mare Serenitatis or Sea of Serenity is at right and up. Mare Tranquillitatis or Sea of Tranquillity is at right center. Oceanus Procellarum is at left center. South Pole is in Aitken Basin on far side.
phases
Moon has phases. New moon is thin crescent. Crescent moon is fuller. First-quarter moon has light on left half, with Sea of Tranquility and Pyrenees Mountains. Gibbous moon is between first quarter and full. Full moon is a circle. Gibbous moon is between third quarter and full. Third-quarter moon has light on right half, with Sea of Shadows and Carpathian Mountains. Crescent moon is less. New moon is thin crescent.
Physical Sciences>Astronomy>Solar System>Moon
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Date Modified: 2022.0224