moon: Physical Characteristics

The study of the moon's surface increased with the invention of the telescope by Galileo in 1610 and culminated in 1969 when the first human actually set foot on the moon's surface. The physical characteristics and surface of the moon thus have been studied telescopically, photographically, and more recently by instruments carried by manned and unmanned spacecraft (see space probe and space exploration). The moon's diameter is about 2,160 mi (3,476 km) at the moon's equator, somewhat more than 1⁄4 the earth's diameter. The moon has about 1⁄81 the mass of the earth and is 3⁄5 as dense. On the moon's surface the force of gravitation is about 1⁄6 that on earth. It has been established that the moon completely lacks an atmosphere, but several space probes have found evidence of water ice in the soil, generally in areas toward the poles. At its most extreme, the surface temperature can rise to above 125℃ (257℉) at lunar noon at the equator and can sink below −245℃ (−409℉) at night in the northern polar region. The gross surface features of the moon are visible to the unaided eye and were first studied telescopically in 1610 by Galileo.

Sections in this article:

• Introduction
• Formation and Evolution
• Internal Structure
• Surface Features
• Physical Characteristics
• Tidal Influence of the Moon
• Solar and Lunar Eclipses
• Retarded Lunar Motion
• The Lunar Orbit and Phases
• The Lunar Month
• The Earth-Moon System
• Bibliography

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