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The effective temperature (Teff, Teff, or what is often meant by black-body temperature, TBB) of an astronomical body such as a star or planet is the calculated temperature of a black body of the same size with the same bolometric luminosity, i.e., the same total radiation energy output rate. It can be considered an estimate of the body's surface temperature, imperfect for being determined at a distance and because a star's surface itself is ambiguous: the radiation reaches us from more than one depth into the star, and these layers have differing temperatures. The various temperature determination methods in use differ but do have some general agreement. Among other measures are brightness temperatures (based on a single wavelength or narrow passband) and color temperatures (based on a color index).