Temperatures of astronomical objects range from almost absolute zero to millions of degrees. Temperature can be defined in a variety of ways, and its numerical value depends on the specific definition used. The temperature is welldefined only in a state of thermodynamic equilibrium. Since most astrophysical objects are not in equilibrium, they cannot be assigned a unique temperature. For many purposes it is still useful to describe phenomena in terms of a temperature, but its value will then depend on how it is defined.
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