Dear Tom,
I noticed in the Tribune almanac for January 3, there was no moonrise, but there was a moonset at 11:31 A.M. How can the moon set if it does not rise? Does this have something to do with the phases of the moon?
Kevin E. Wilson
Dear Kevin,
On average, the moon rises about 50 min. later each night, depending on Earth’s season, so the lunar day is about 1 hour longer than the terrestrial day as seen from Earth. Once a month –and it’s always around the last quarter moon–this extra hour difference has to be reckoned with and there will be no moonrise. In the current lunar cycle, moonrise for Jan. 2 was 11:32 p.m., on Jan. 3 there was no moonrise, and on Jan. 4, moonrise occurred at 12:38 a.m., some 25 hours between consecutive moonrises. A missing day also occurs with moonset at the first quarter moon, but that happens about noon when nobody notices.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
