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waar <math>r</math> is die afstand van die waarnemer na die ligbron.
ItDaar has beenis showngetoon thatdat thedie luminosityhelderheid ofvan a'n starster <math>L</ math> (assumingas theaanvaar starword isdat die ster a'n [[blackswart bodyliggaam ]] is , whichwat is'n agoeie goodbenadering approximationis ) isook alsoverwant relatedaan todie temperaturetemperatuur <math>T</math> anden radius <math>R</math> ofvan thedie starster byis thedeur equationdie vergelyking :<ref name="AUSTRALIA2004"/>
:<math>L = 4\pi R^2\sigma T^4 \,</math> ,
waar
where
:σ is the [[Stefan–Boltzmann constant]] konstante 5.67{{e|−8}} [[Watt|W]]·m<sup>-2</sup>·K<sup>-4</sup>.
DividingGedeel bydeur thedie [[Solarson luminosity|luminosityse of the Sun]]helderheid <math>L_{\odot}</math> anden cancellingkanselleer constantskonstantes , weword obtaindie thevolgende relationshipverwantskap gekry :<ref name="AUSTRALIA2004"/>
:<math>\frac{L}{L_{\odot}} = {\left ( \frac{R}{R_{\odot}} \right )}^2 {\left ( \frac{T}{T_{\odot}} \right )}^4</math> ,
wherewaar <math>R_{\odot}</math> anden <math>T_{\odot}</math> are thedie radius anden die temperatuur temperaturevan ofdie theson Sun,onderskeidelik respectivelyis .
Vir sterre op die [[hoofreeks]] is helderheid ook soos volg verwant aan die massa van die ster:
For stars on the [[main sequence]], luminosity is also [[mass–luminosity relation|related to mass]]:
:<math>\frac{L}{L_{\odot}} \approx {\left ( \frac{M}{M_{\odot}} \right )}^{3.9}</math> .
