Solar luminosity

The solar luminosity (L☉) is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun.

One nominal solar luminosity is defined by the International Astronomical Union to be 3.828×1026 W.[2] The Sun is a weakly variable star, and its actual luminosity therefore fluctuates.

Solar irradiance is responsible for the orbital forcing that causes the Milankovitch cycles, which determine Earthly glacial cycles.

The mean irradiance at the top of the Earth's atmosphere is sometimes known as the solar constant, I☉.

Irradiance is defined as power per unit area, so the solar luminosity (total power emitted by the Sun) is the irradiance received at the Earth (solar constant) multiplied by the area of the sphere whose radius is the mean distance between the Earth and the Sun:

Evolution of the solar luminosity, radius and effective temperature compared to the present-day Sun. After Ribas (2010) [ 1 ]