I've been trying to wrap my head around the relationship between temperature increase of an object at a distance and temperature of a heat source. From what I've found, the temperature increase of an object from thermal radiation is affected by the inverse square law. This classroom experiment seems to show an inverse-square relationship between temperature change and increasing distance, and I've found similar answers elsewhere. Is it possible to determine the temperature of a heat source based on temperature increase of an object a certain distance away? Would this work for much larger scales? For example, if an object (say, in a vacuum to keep things simple) is 500 radii away from the heat source and experiences a temperature increase from 298 K to 300 K, does that mean the temperature of the heat source is (300 K * 500^2) = 75,000,000 K?