A physics stack question asks why when the air is hotter then your body thermodynamics allows your body to operate as a heat engine as a heat engine must have a sink for waste heat. See question here, http://physics.stackexchange.com/questions/59316/human-as-a-heat-engine Part of the answer is that normally the sky (except for the sun) is a net heat sink not a net heat source, if we point our hands to a clear sky our palms would sense cold? A clear sky is even colder then an overcast sky? Other fun with an infrared sensor? Edit, point your hands towards the sky and away from the sun for a cooling effect? With infrared thermometer in hand I measured plastic tarp in the shade, the overcast sky, inside my mouth. The outside temp was 47F in the shade by a standard thermometer. plastic outside in shade, 48F overcast sky (cloud ceiling at 7500ft), 19F inside of my mouth, 97.7F. So part of what keeps us from overheating is the fact that the sky is relatively cool? Thanks for any help!