The temperature of the surface of a celestial body, as opposed to its underlying layers (for example, the central temperatures of stars are vastly greater than their surface temperatures). The surface temperature a star would have if it radiated exactly like a black body of the same size and energy output is called its effective temperature. The colour temperature of a star is found by comparing its energy distribution at different wavelengths with that of a black body; this usually differs from the effective temperature because stars are not perfect black bodies. In practice, a star’s surface temperature is an average of the temperatures of a series of layers at different heights in its photosphere. A planet’s surface temperature depends on the relative amounts of solar radiation absorbed by the planet and the radiation emitted by its surface.