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The Moon
Did you ever know where the word "month" came from? That's right you guessed it, the "Moon"...
The Moon is the Earth's satellite. It's elliptical with an average distance from Earth of 380,000 km and a period of 27.3 days. It is much smaller than the Earth: about one-fourth the Earth's radius and about 1/81 its mass. It has a crust approximately 65 km thick on the far side of the Moon and about 150 km on the near side (this will be explained shortly). Its small size has allowed its internal heat to escape, keeping its core cool, thereby preventing plate tectonic motions. The Moon has no atmosphere because it is too cool to create one by volcanic outgassing and too small for its low gravity to retain gases even if an atmosphere had formed.
With neither atmosphere nor tectonic activity, the Moon's surface is unaltered except by impact features: craters, rays, and the maria. Maria are enormous lava flows that have flooded into basins made by large impacting bodies late in the Moon's formation. The bright areas that surround the maria are highlands. They differ in brightness because they are composed of different rock types. The maria are basalt, a dark, congealed lava rich in iron, magnesium, and titanium silicates. The highlands are mainly anorthosite, a rock type rich in calcium and aluminum silicates. Astronauts made these discoveries possible.
The Moon may have formed when a Mars-sized body collided with the Earth and splashed material from the Earth into orbit. That debris, drawn together by its own gravity, would then have reassembled into the Moon.
The Moon's shadow sometimes falls onto Earth, causing a solar eclipse. The special thing about these is that the Moon just covers the Sun.Its distance from the Sun compensates for its small size. Therefore, the shadow lies on small parts on the Earth and so astronomers have to travel to view them. When the Earth's shadow falls onto the Moon, we see a lunar eclipse like the one below. This does not occur monthly because the Moon's orbit is tilted at an angle of 5 degrees.
The Moon's gravity creates tides depending on which part of the Earth is closest to the Moon, and as the Earth rotates beneath the tidal bulge of the ocean, our planet's rotation is slowed. This is where the terms "high tide" and "low tide" come from. Similar tidal braking exerted by the Earth on the Moon has slowed the Moon's spin, making it synchronous with its orbital motion around the Earth.
| Solar eclipses | Lunar eclipses |
| Feb. 26,1998 | Northwest South America and Caribbean | Sept. 16,1997 | Australia, most of Asia, most of Africa and Europe |
| Aug. 11, 1999 | Greenland, Europe, Southern Asia | Jan 21, 2000 | North and northwest Asia, Europe, North America, South America |
| June 21,2001 | Southern Africa/Madagascar | May 16,2003 | Antarctica, most of Africa and Europe, most of the Americas |
| Dec. 4,2002 | Southern Africa, Australia | Nov. 8/9,2003 | Most of Asia, Africa, Europe, The Americas except extreme SW Alaska |
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