It's Kansas. It's May. And yet it's not quite 60 degrees F. Clouds are rolling in, blotting out the sun. Amazing thing, the sun: When it's shining on one's face - even at this temperature - one feels pleasantly warm. When a cloud obscures the sun, one shivers in the Mount Oread breeze.
Radiation is magic. Think about it for a moment: The sun is busily converting helium and hydrogen into pure energy at a distance of 149,600,000 km. That's, like, farther than you could drive a car in your lifetime. And yet! That little one-degree-wide disc of orange in the sky makes you warm when it is visible, and when it's hidden behind a cloud, you feel how cold the world is without it.