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.
