Star Luminosity Calculator
Astronomy & SpaceCalculate a star luminosity relative to the Sun, based on its radius and surface temperature.
Luminosity (Solar Units)
The star total energy output relative to the Sun, using the Stefan-Boltzmann law (luminosity scales with radius squared times temperature to the fourth power).
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Frequently Asked Questions
Why does temperature affect luminosity so much more than radius?
Luminosity scales with temperature to the fourth power but only radius squared, so even a modest temperature increase has a much larger impact on total energy output than a similar proportional increase in size.
What is the Sun surface temperature used as the baseline?
The Sun surface temperature is approximately 5,778 Kelvin, used here as the reference point so results are expressed in convenient solar luminosity units rather than raw physical units like watts.
Why are some small stars extremely luminous?
A star with very high surface temperature can be highly luminous even at a modest size, since temperature has an outsized effect in the luminosity formula — this is common among hot blue stars.
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