Star Luminosity Calculator
Estimate a star's intrinsic luminosity with the Stefan–Boltzmann law. Supply the star's radius and effective temperature to reveal how many watts of energy it emits each second, perfect for comparing stellar classes or checking astrophysics homework.
Assumes an ideal blackbody star with uniform surface temperature.
Examples
- Solar analog: 6.96×10⁸ m radius at 5,778 K ⇒ 3.85×10²⁶ watts
- Red giant: 3.0×10¹⁰ m radius at 3,200 K ⇒ 1.26×10²⁹ watts
- White dwarf: 7.0×10⁶ m radius at 20,000 K ⇒ 2.22×10²⁵ watts
FAQ
What constant is used?
The calculation uses the Stefan–Boltzmann constant 5.670374419×10⁻⁸.
Are inputs in SI units?
Yes, radius in meters and temperature in Kelvin.
Does it assume a perfect blackbody?
Yes, real stars may differ slightly.
How do I express the answer in solar luminosities?
Divide the watt value by the Sun's luminosity (3.828×10²⁶ W) to convert to L☉.
Does interstellar dust change the luminosity?
Dust only dims the light we see; it does not alter the star's intrinsic luminosity computed here.
Additional Information
- Luminosity (L) equals 4πR²σT⁴, where σ is the Stefan–Boltzmann constant 5.670374419×10⁻⁸ W·m⁻²·K⁻⁴.
- Because temperature is raised to the fourth power, small changes in T produce dramatic shifts in luminosity.
- Apparent brightness also depends on distance; pair this result with the inverse square law to model observed magnitudes.