Calculating stellar temperature at a distance?

How does one calculate the temperature of the space surrounding a
stellar body at a certain distance from it? I was just using an inverse
square relationship between temperature and distance, but that comes up
with non-sense results.

Let's take the Earth and Sun as an example. If the Sun's surface
temperature is 9000K, and its radius is 700,000 km, and the Earth is 1
AU (1.5E+8 km) away from the Sun. At that distance using an inverse
square relationship, I get 0.2K as the answer. Obviously the Earth is
much warmer than that. What's the real way to obtain temperature here?

Yousuf Khan