So i've been given a problem in my thermodynamics class and it is completely confusing me. Here is the problem: "Measured from the time when the first rays of sunshine appear above the horizon until the moment when the sun is fully visible, sunrise lasts 2.1 minutes. Based on this information, and assuming that the earth and the sun are “black bodies”, can you estimate the temperature of the sun?" Now I don't even have any clue what the teacher is getting at. I suppose that using that time i can estimate the velocity of the sun. I don't see how this will lead me towards an estimate of the sun's temperature since I can not assume the sun's kinetic energy is due to thermal energy. Can anyone give me a hint as to what i should even be thinking about? thanks.