# What Do You Think About That A 1879 Stefan's Law Be Used To Calculate Star Radius Or Temperature?

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### #1 rhertz

rhertz

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Posted 29 April 2019 - 11:11 PM

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 Luminosity
• Star Surface temperature

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

L = 4 π R2 σ Τ 4

L: Luminosity (in Watts)

T: Star's surface temperature.

Stefan-Boltzmann Constant  σ=5.67×10−8W.m-2K-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 = T4

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.