Dear Tom,
Why is it that sometimes in the early evening the moon is visible in the eastern sky, and sometimes in the west? Can you explain its rotation?
Walter Franiak, Arlington Heights.
Dear Walter,
As the Earth turns on its axis, the moon, like most celestial objects, appears to rise in the east and set in the west. In this westward march, the moon moves eastward about 12(degrees) per day in respect to the sun. As a result, the moon rise averages about 50 minutes later each day. This really adds up. In the course of a week, the moon rises and sets almost 6 hours later and has crossed almost 1/2 of the overhead sky. Additionally, the phase of the moon–determined by the amount of bthe lunar surface in sunlight as seen from Earth, changes a little each day. The whole process of one lunar cycle takes about 29.5 days.
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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 Dennis Haller and Richard Koeneman plus weather producer Bill Snyder contribute to this page.
