The solar luminosity ( ) is a unit of radiant flux (power emitted in the form of ) conventionally used by to measure the luminosity of , galaxy 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 .
The Sun is a weakly variable star, and its actual luminosity therefore Solar variation.
Determination
Solar luminosity is related to
Irradiance (the
solar constant). Slow changes in the axial tilt of the planet and the shape of its orbit cause cyclical changes to the solar irradiance. The result is
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, . 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:
where is the unit distance (the value of the astronomical unit in
) and is a constant (whose value is very close to one) that reflects the fact that the mean distance from the Earth to the Sun is not exactly one astronomical unit.
See also
Further reading
External links
