Blackbody Temperature
The effective temperature at which a blackbody emits blackbody radiation.
Plack Energ
The Planck energy is the average energy of an oscillator, 
(1)
The Planck postulate states that 
(2)
where n is a nonnegative integer, h is Planck's constant, and 
is the frequency of radiation. Maxwell-Boltzmann statistics give 
(3)
where C is a constant, k is Boltzmann's constant, and T is the temperature. Plugging in, 
(4)
Planck Intensity Density
In terms of frequency, the energy flux from blackbody radiation is given by
where
is the average energy density,
is
Planck energy,
N is the number density of oscillators,
h is
Planck's constant,
k is
Boltzmann's constant, and
T is the
temperature. Here,
(2)
is the number of cells per unit phase space. The factor of 2 must be added since two electrons with opposite spins may occupy the same element of phase space. The
momentum of a
photon is given by
(3)
so
(4)
and
(5)
where
is an element of solid angle. Plugging in,
Planck Law
Planck Law
The Planck law gives the intensity radiated by a blackbody as a function of frequency (or wavelength). Let a blackbody have temperature T. Let 
be the energy density per unit solid angle so that 
(1)
(2)