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. One solar luminosity is equal to the current accepted luminosity of the Sun, which is 3.839×1026 W, or 3.839×1033 erg/s. The value is slightly higher, 3.939×1026 W (equivalent to 4.382×109 kg/s or 1.9×10−16 M☉/d) if the solar neutrino radiation is included as well as electromagnetic radiation. The Sun is a weakly variable star and its luminosity therefore fluctuates. The major fluctuation is the eleven-year solar cycle (sunspot cycle), which causes a periodic variation of about ±0.1%. Any other variation over the last 200–300 years is thought to be much smaller than this.
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“Our civilization has decided ... that determining the guilt or innocence of men is a thing too important to be trusted to trained men.... When it wants a library catalogued, or the solar system discovered, or any trifle of that kind, it uses up its specialists. But when it wishes anything done which is really serious, it collects twelve of the ordinary men standing round. The same thing was done, if I remember right, by the Founder of Christianity.”
—Gilbert Keith Chesterton (1874–1936)