Interactive Simulator · Astronomy and cosmology

A star's thermal glow

A star radiates almost as a perfect black body. Its spectrum has a single peak whose wavelength obeys Wien's law, λₘₐₓT = 2.90 × 10⁻³ m K: hotter stars peak at shorter (bluer) wavelengths. The total power radiated obeys the Stefan-Boltzmann law, L = 4πσr²T⁴. Drag the temperature and watch the peak slide blue and the colour change; combine L and T to estimate the radius.

Mission Heat the star and watch the peak march toward the blue while the whole curve climbs. Cool it and the peak slides into the red. Streak 0Best 0
If the surface temperature doubles, the peak wavelength λₘₐₓ of the spectrum:
temperature T5800 K
peak wavelength λₘₐₓ = 2.90×10⁻³/T500 nm (yellow-white)
power per area σT⁴—
luminosity L = 4πσr²T⁴1.0 L☉
Wien fixes where the peak sits; Stefan-Boltzmann fixes the total output. Measure the colour (so T) and the luminosity (so L), and you can solve L = 4πσr²T⁴ for the radius r.