Brightness temperature

In 1928, Nyquist showed that the noise power per unit bandwidth produced by a resistor of resistance, $R$, and physical temperature, $T_{}$, is

$\displaystyle \ensuremath{dw}= \ensuremath{k}\,\ensuremath{T_{}}.$ (73)

This relationship indicates that any spectral power can be expressed as a temperature using this relationship. For instance, the observed main beam temperature is defined as

$\displaystyle \ensuremath{T_{\ensuremath{\mathrm{mb}}}}(\ensuremath{\theta_{0},...
...{0}-\phi_{}},\ensuremath{\nu}) \, d\ensuremath{\Omega_\ensuremath{\mathrm{}}}}.$ (74)