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The albedo of an object is its optical reflectivity, i.e., the extent to which it reflects light.   Albedo is a measure of reflectivity of a surface or body. It is the ratio of electromagnetic radiation (EM radiation) reflected to the amount incident upon it. The fraction, usually expressed as a percentage from 0% to 100%, is an important concept in climatology and astronomy. This ratio depends on the frequency of the radiation considered: unqualified, it refers to an average across the spectrum of visible light. It also depends on the angle of incidence of the radiation: unqualified, normal incidence. Fresh snow albedos are high: up to 90%. The ocean surface has a low albedo. Earth has an average albedo of 39%.