Stellar Luminosity Calculator: Star Power Output vs the Sun

Stellar Luminosity Calculator

Calculate a star's total power output (luminosity) relative to the Sun based on its radius and surface temperature.

Radius (Solar Radii, R☉)

Sun = 1.0, Betelgeuse ≈ 700.

Temperature (Kelvin)

Sun = 5778 K.

Total Luminosity 1.00e+0 L☉

Times brighter than the Sun

What is Stellar Luminosity?

Luminosity is the total amount of energy emitted by a star per unit of time. It is an intrinsic property of the star, independent of its distance from the observer.

The Stefan-Boltzmann Law

A star's luminosity depends on two factors: its size (surface area) and its temperature. Because luminosity is proportional to the fourth power of the temperature (T⁴), even a small increase in temperature results in a massive increase in energy output.

Frequently Asked Questions (FAQ)

What is the most luminous star?

Stars like R136a1 can be several million times more luminous than our Sun.

How does luminosity relate to magnitude?

Absolute magnitude is a logarithmic measure of a star's luminosity.

How it Works

This calculator applies the Stefan-Boltzmann law L = 4πR²σT⁴, expressed in solar units: L/L☉ = (R/R☉)² × (T/5778 K)⁴. The radius you enter (in solar radii) is squared, the temperature is divided by the Sun's effective temperature of 5778 K and raised to the fourth power, and the two factors are multiplied to give the luminosity in solar luminosities (L☉).

User Guide

Enter the star's radius in solar radii — the Sun is 1.0 and Betelgeuse is roughly 700.
Enter the star's surface temperature in Kelvin — the Sun is 5778 K.
Read the total luminosity in the blue result box, shown in scientific notation as a multiple of the Sun's output.
Experiment with the values: doubling the temperature multiplies the luminosity by 16, because of the T⁴ dependence.