Solar Flux at Distance Calculator
Calculate the solar irradiance at any distance from the Sun.
Compare to Earth's solar constant of 1,361 W/m².
Includes planet presets.
Solar flux (irradiance) is the power per unit area received from the Sun at a given distance.
Formula:
F = L☉ / (4πd²)
Where:
- L☉ = solar luminosity = 3.828 × 10²⁶ W
- d = distance from the Sun (meters)
- F = irradiance (W/m²)
The inverse-square law: Because light spreads out spherically, doubling the distance reduces flux by a factor of 4. This is why Mercury is much hotter than Mars — not just because it’s closer, but because it’s inside closer to the Sun.
Simplified formula:
F = 1361 W/m² × (1 AU / d)²
where the solar constant (1,361 W/m² at 1 AU) is measured above Earth’s atmosphere.
Solar flux at each planet:
| Planet | Distance (AU) | Flux (W/m²) |
|---|---|---|
| Mercury | 0.387 | 9,082 |
| Venus | 0.723 | 2,601 |
| Earth | 1.000 | 1,361 |
| Mars | 1.524 | 586 |
| Jupiter | 5.203 | 50.3 |
| Saturn | 9.537 | 14.9 |
| Uranus | 19.19 | 3.69 |
| Neptune | 30.07 | 1.51 |
Equilibrium temperature: A body at distance d with albedo A reaches an equilibrium temperature:
T_eq = (F(1-A)/(4σ))^(1/4)
where σ = 5.67 × 10⁻⁸ W/m²/K⁴ (Stefan-Boltzmann constant).