In astrophysics, since Stefan proposed his empirical formula in 1879, a star is considered

to be close to the idea of an ideal blackbody.

Since then, variationd of the Stefan Law is widely used to determine some basic properties of a star, like:

- Star Radius
- Star Luminosity
- Star Surface temperature

To calculate any given star Luminosity, Stefan's law is expressed as:

**L = 4 π R ^{2} σ Τ ^{4}**

^{L: Luminosity (in Watts)}

^{R: Star radius}

^{T: Star's surface temperature}^{.}

^{−8}W.m

^{-2}K

^{-4}

^{This is a variation of the original Stefan's formula, widely used to calculate any star temperature by finding the absolute luminosity}

^{based in relative comparations with proper references:}

*j** = **T*^{4}

where j is the Iradiance or Flux Density (Watt/m^2), which is estimated by comparisons with references (like our Sun's Irradiance).

What do you think about the fact that this formula has been used for **140 years **without modifications?

**Personal note**: Achievements from the golden period at physics (1850 - 1900), in thermodynamics and electromagnetism, are

*unsurpassed in certainty, simplicity and coberture. This law, along with Wien's law (1893) and Planck's law (1900) conform a*

*set of laws for the radiation of black body surfaces and cavities, and are all of them mathematically related:*

*Planck's Law is the master law for radiation of black body cavities.**Wien's Law of displacement is a linear relationship between peaks of spectral graphs of the Planck's Law (by derivates).**Stefan's Law of irradiating power of a BB is the integral area of the Planck's formula for density irradiance.*

*Also, Kirchoff's laws for spectroscopy (1860-1862), which explain absorption lines in the spectra of celestial bodies is the core of*

*the Hubble's law (1929) for the spectrum shifting of celestial bodies emission, being all of them non-relativistic and being used today.*

*But, as a critic, efforts to find relativistic replacements continue relentlessly.*

**Edited by rhertz, Yesterday, 06:36 AM.**