Nominal Solar Luminosity
| Value | 3.828e26 W |
| Status | Exact by definition — no uncertainty |
| Source | IAU 2015 Resolution B3 |
| Categories | Astronomicalsolar-systemstellar |
| milliwatt | 3.8280000e+29 mW |
| watt | 3.8280000e+26 W |
| kilowatt | 3.8280000e+23 kW |
| megawatt | 3.8280000e+20 MW |
| horsepower (mechanical) | 5.1334326e+23 hp |
| BTU per hour | 1.3061678e+27 BTU/h |
| ton of refrigeration | 1.0884732e+23 ton |
Learning zone
The Sun's total radiant power follows from one measurement and one sphere: take the total solar irradiance at Earth's distance, about 1361 W/m², and multiply by the area of a sphere of radius one au. The nominal value fixed by the IAU in 2015 is exactly 3.828 × 10²⁶ W, deliberately rounded so that it does not change when irradiance monitoring improves, and so that "L = 10⁵ L⊙" means the same thing in every paper.
The real Sun varies by about 0.1 per cent over the 11-year sunspot cycle — enough to matter for climate reconstructions, nowhere near enough to matter for stellar classification. For scale, that output is roughly 10¹⁴ times humanity's entire primary energy consumption, and it comes from converting about 4.3 million tonnes of mass into energy every second in the core.