I was running on a cold but sunny day early this week, when one aspect of my tiny portion of the physical universe struck me as fascinating. I left the warmth of my house and started running with the air at about 10 degrees. The first few blocks were chilling because I was underdressed, knowing I would warm up as I ran. I soon rounded a corner to face the bright sun, low on the horizon as it is this time of year.

I was immediately warmed by the solar radiation and impressed by the fact that those rays had traveled through some 93 million miles largely of space as well as about 300 miles of thin outer-atmosphere before reaching the 10 miles of dense, lower atmosphere and passing through all of this largely unaffected, to warm my face.

Solar radiation directly warming human skin is not reflected by the air temperature, nor is it considered in the wind chill factor. It made a noticeable difference, nonetheless.

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