Lsun
solar luminosity
Powerexact by definition
The solar luminosity is defined by IAU resolution as exactly 3.828 × 10²⁶ watts, a nominal value chosen to sit within the uncertainty of the real sun. Stellar luminosities are quoted as multiples of it because the ratio is what observation actually measures, and the ratio is far better known than either absolute value.
Watch out: The real sun is not exactly this and does not hold still: total solar irradiance varies by about 0.1 percent over the eleven-year cycle. The IAU fixed the nominal value precisely so that published stellar results would not shift every time the solar measurement was refined.
| 1 Lsun | 3.8280000e+26 W |
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