My reference for the following equations is an excellent engineering text for practicing engineers entitled Heat Transfer Professional Version by Lindon C. Thomas, 1st edition, Prentice-Hall, Englewood Cliffs, New Jersey, 1993. The equations themselves are based upon work by Duffie and Beckman, published in Solar Energy Thermal Processes, John Wiley & Sons, New York, 1974.

I have found this data quite handy for making accurate estimates of the thermal equilibrium temperature of outdoors surfaces exposed to the night sky. For example, will an exposed surface temperature drop below the dew point during the night? Is it possible that a...