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Physical Features of Moon

Physical Features of the Moon The Moon is almost unique in the solar system in that it is quite large compared with its primary, Earth; if put in comparison to other planets and its subordinate satellites. The Moon's diameter is 3,476 km, about 1\4 the diameter of the Earth. By comparison, the satellites of Jupiter and Saturn are about 1/100 the size of their primary. Table 1.1 shows the overall physical and orbital properties of the Moon. The average density of the Moon is 3.312 (water is 1.0), which is only about 3/5 that of the Earth. Since the surface rocks are essentially the same, this means that the Moon's interior must somehow be different from Earth's. The Moon has no free water and essentially no atmosphere. Table 1.1 Properties of the Moon, compared with Earth The Moon is tidally locked to the Earth, such that we always see the same side. Thus we refer to the "near side" and the "far side". In order for tidal locking to occur, the Moon must rotate on its axis at the same average rate that it revolves around the Earth. The Moon has a very low albedo, which means that it reflects very little of the light that falls on it. It appears bright in the sky, but that is only because of the contrast between the lunar surface and the deep blackness of the night sky. In reality, the surface of the Moon is about as bright as coal dust. Temperatures of the Moon's equator range from 127°C (261°F) at midday to -173°C (-279°F) shortly before lunar dawn. The extreme temperatures are due to the fact that there is no blanket of air or water to moderate the temperatures. Surface temperatures at the lunar poles are much colder, ranging from -113°C to -258°C due to the very low incidence angle of sunlight. Thus, although it is much colder at the poles than at the equators, there is also less temperature variation, a fact which may prove useful for the operation of machinery and habitats. The Moon, like the Earth, has mountain ranges and valleys. However, the origin of these features was very different for the Moon than for the Earth.