What is the solar luminosity?

3.828 × 10²⁶ watts. It is a standard unit for expressing other stars' luminosities.

How does luminosity differ from brightness?

Luminosity is an intrinsic property (total power). Brightness (flux) is what we measure, and it diminishes with distance.

From about 10⁻⁴ L_sun for the faintest red dwarfs to over 10⁶ L_sun for the most luminous supergiants.

Calculate the luminosity of a star from its flux and distance using L = 4 pi d^2 F.

Observed Flux

W/m²

Distance

Luminosity

382,764,080,942,341,600,000,000,000.000 W

In Solar Luminosities0.9999 L_sun

Luminosity vs Observed Flux

Luminosity is the total power output of a star. If we measure the flux (power per unit area) at a known distance:

L = 4π d² F

The Sun's luminosity is 3.828 × 10²⁶ W, and its flux at 1 AU is about 1361 W/m² (the solar constant).

The Sun: flux = 1361 W/m² at 1 AU (1.496e11 m).

Compute flux from luminosity and distance.

Find luminosity from temperature and radius.

See how brightness changes with distance.