šŖ Habitable Zone Calculator
Enter a star’s luminosity relative to the Sun to estimate the inner and outer boundaries of its habitable zone, where liquid water could exist on a planet’s surface.
What is the habitable zone?
The circumstellar habitable zone, sometimes called the ‘Goldilocks zone,’ is the range of orbital distances around a star where a rocky planet could maintain liquid water on its surface given a suitable atmosphere.
The formula
This calculator uses a simplified version of the standard inverse-square flux relation: the habitable zone distance scales with the square root of a star’s luminosity relative to the Sun. The inner edge is estimated at r = √(L ÷ 1.1) AU, and the outer edge at r = √(L ÷ 0.53) AU, using commonly cited flux thresholds for the runaway greenhouse and maximum greenhouse limits.
Real habitable zone boundaries also depend on a planet’s atmospheric composition, cloud cover, and reflectivity, so this is a simplified estimate, not a precise habitability prediction. It’s intended for general astronomy education.