1.6 Earth’s Moon: Diameter, Density, Gravity, and the Terrain that makes the Face of the Man in the Moon

1.6 Earth’s Moon: Diameter, Density, Gravity, and the Terrain that makes the Face of the Man in the Moon

Today Earth has hundreds of satellites, but only one, the moon, is natural. Although other planets have moons, our planet satellite system is unique in the solar system because Earth’s moon is unusually large compared to its parent planet. The diameter of the Moon is 3475 kilometers (2150 miles) about one-fourth of Earth’s 12,756 kilometers (7920 miles).

From a calculation of the Moon’s Mass, its density is 3.3 times that of water. This density is comparable to that of mantle rocks on the Earth, but it’s considerably less than Earth’s average density, which is 5.5 times that of water. Geologists have suggested that this difference can be accounted for if the Moon’s iron core is small.

The gravitational attraction at the lunar surface is 1/6 of that experienced on Earth’s surface. A 150 lb. person on Earth weighs only 25 pounds on the Moon, although they still have the same mass. This difference allows an astronaut to carry a heavy life support system with relative ease. If not burdened with such a load, an Astronaut could jump six times higher than on Earth.

When Galileo first pointed his telescope toward the moon, he saw two different types of terrain, dark lowlands and brighter, highly cratered highlands. Because the dark regions resemble Seas on Earth, they were called “maria”. “Mar” equals “sea”. Today we know that the maria are not oceans, but instead are flat plains that resulted from immense outpouring of fluid basaltic lavas. By contrast, the light colored areas resemble Earth’s continents so the first observers dubbed them “terrae”, Latin for land. Today these areas are generally reflect referred to as lunar highlands, because they are elevated several kilometers above the maria. Together the arrangement of Terrae and Maria results in the well-known face of the Moon.


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