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Albedo, in astronomy, the reflecting power of a celestial body that is not self-luminous. Albedo is stated as a decimal fraction between 1 and 0. An albedo of almost 1 indicates a bright surface that reflects most of the light that strikes it. An object with an albedo of almost 0 would absorb most of the light that struck it; little light would be reflected. The moon, for example, with an albedo of 0.07, reflects only 7 per cent of the sunlight it receives. Albedo is determined by calculating the amount of light that strikes the body and then measuring the reflected light.

The concept of albedo is useful for attempting to determine the nature of planetary surfaces and atmospheres. For example, a planet surrounded by clouds would have a high albedo; one with no clouds and a surface composed of dark, rough rock would have a low albedo. Albedos of some of the planets are: Mercury, 0.06; Venus, 0.76; Earth, 0.34; Mars, 0.15; Jupiter, 0.41; and Saturn, 0.42.

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