For a planet around another star, (the incident stellar flux on the planet) is not a readily measurable quantity. To find the equilibrium temperature of such a planet, it may be useful to approximate the host star's radiation as a blackbody as well, such that:
The luminosity () of the star, which can be measured from observations of the star's apparent brightness, can then be written as:
 where the flux has been multiplied by the surface area of the star.
To find the incident stellar flux on the planet, , at some orbital distance from the star, , one can divide by the surface area of a sphere with radius :
Plugging this into the general equation for planetary equilibrium temperature gives:
If the luminosity of the star is known from photometric observations, the other remaining variables that must be determined are the Bond albedo and orbital distance of the planet. Bond albedos of exoplanets can be constrained by flux measurements of transiting exoplanets, and may in future be obtainable from direct imaging of exoplanets and a conversion from geometric albedo. Orbital properties of the planet such as the orbital distance can be measured through radial velocity and transit period measurements.
Alternatively, the planetary equilibrium may be written in terms of the temperature and radius of the star: