An Etymological Dictionary of Astronomy and Astrophysics

An approximate empirical relation between the rate of → heat transfer to or from an object and the temperature difference between the object and its surrounding environment. When the temperature difference is not too large: dT/dt = -k(T - T_s), where T is the temperature of the object, T_s is that of its surroundings, t is time, and k is a constant, different for different bodies.

See also: → Newton; → law; → cooling.