Dear Tom,
The Earth’s surface is always split 50-50, the part receiving direct sunlight and the part not receiving it. That’s common sense, but a friend claims there is always more daylight than darkness (excluding twilight). Please shoot him down.
–Ken Nathanson
Dear Ken,
Reality sometimes defies common sense. Your friend is correct: There is more sun than no sun. Here’s why: The sun is not a point in space. Triton College astronomer Dan Joyce says direct sunlight first reaches a given spot the moment the top of the sun’s disk pokes above the horizon at sunrise; at sunset, sunlight continues until the top of the disk sinks below the horizon. The sunrise/sunset minutes when only a portion of the solar disk is above the horizon add to daylight time. Also atmospheric refraction makes the sun appear higher in the sky, lengthening daylight by a few minutes.
———-
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or: asktomwhy@wgntv.com
Weather Report is prepared by the WGN-TV Weather Center, where Tom Skilling is chief meteorologist. His forecasts can be seen Monday through Friday on WGN News at 11:30 a.m., 5:30 p.m. and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
IN THE WEB EDITION: For updated weather news, forecasts by ZIP code and local radar images, go to chicagotribune.com/weather or wgntv.com
