The equivalent temperature which represents the unwanted noise from an antenna produced by ground radiation, atmospheric attenuation, and other sources (in the absence of an astronomical signal) according to
where k is Boltzmann's constant, is the system temperature, is a given frequency interval, is the receiver temperature (which represents internal noise from the receiving amplifier), and is the "antenna temperature" which represents the unwanted noise from the antenna produced by ground radiation, atmospheric attenuation, and other sources. (Note that there is actually a second nonequivalent definition of antenna temperature.)
