Units of measurement in astronomy | Units of power
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. This does not include the solar neutrino luminosity, which would add 0.023 L☉, or 8.8×1024 W, i.e. a total of 3.916×1026 W (the mean energy of the solar photons is 26 MeV and that of the solar neutrinos 0.59 MeV, i.e. 2.27%; the Sun emits 9.2×1037 photons and as many neutrinos each second, of which 6.5×1014 per m2 reach the Earth each second). The Sun is a weakly variable star, and its actual luminosity therefore fluctuates. The major fluctuation is the eleven-year solar cycle (sunspot cycle) that causes a quasi-periodic variation of about ±0.1%. Other variations over the last 200–300 years are thought to be much smaller than this. (Wikipedia).
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