Nominal Solar Luminosity
| Value | 3.828e26 W |
| Status | Exact by definition — no uncertainty |
| Source | IAU 2015 Resolution B3 |
| Categories | AstronomicalStars & Sun |
| nanowatt | 3.8280000e+35 nW |
| erg per second | 3.8280000e+33 erg/s |
| microwatt | 3.8280000e+32 μW |
| milliwatt | 3.8280000e+29 mW |
| foot pound-force per minute | 1.6940327e+28 ft·lbf/min |
| BTU per hour | 1.3061678e+27 BTU/h |
| watt | 3.8280000e+26 W |
| kilocalorie per hour | 3.2914875e+26 kcal/h |
| foot pound-force per second | 2.8233879e+26 ft·lbf/s |
| thousand BTU per hour | 1.3061678e+24 MBH |
| metric horsepower | 5.2046316e+23 PS |
| horsepower (mechanical) | 5.1334326e+23 hp |
| electrical horsepower | 5.1313673e+23 hp (elec) |
| kilowatt | 3.8280000e+23 kW |
| ton of refrigeration | 1.0884732e+23 ton |
| boiler horsepower | 3.9023396e+22 bhp |
| million BTU per hour | 1.3061678e+21 MMBTU/h |
| megawatt | 3.8280000e+20 MW |
| gigawatt | 3.8280000e+17 GW |
| terawatt | 382,800,000,000,000 TW |
| solar luminosity | 1 Lsun |
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.