Volume 16, Issue 37 - September 11 - September 18, 2008

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Sky Watch by J. Alex Knoll

Night Lights Fleeting and Steady

Setting planets give the Harvest Moon its due

Twilight on Thursday the 11th reveals dazzling Venus less than one-half degree to the upper right of Mars, a dull speck by comparison. Mercury hovers little more than three degrees below the two, and its steady light is far brighter than Mars. Not 10 degrees farther along the horizon to the south shines blue-white Spica of the constellation Virgo.

While Venus is holding steady in the evening sky, Spica, Mercury and Mars are setting fast. Come dusk Tuesday, the four have formed a skewed rectangle, with only six degrees separating the farthest from any other. Your fist held at arm’s length will obscure all four, blotting out a piece of the sky about 10 degrees in circumference. Better yet, all four will fit within the field of view of all but your children’s toy binoculars. But don’t dally, as these four set one after another, and all sink beneath the horizon by 8:15pm.

As twilight gives way to full darkness, only Jupiter begins a lonely vigil, the only planet visible to the unaided eye. Appearing due south at sunset, around 7:15 this week, Jupiter arcs counter-clockwise, setting in the southwest before 1am.

While the planets blink out, the moon shines through the night, reaching full phase Monday, September 15. The full moon closest to autumnal equinox, September 20, is the Harvest Moon. Like all full moons, it rises with the setting sun and sets with daybreak. But not only does the Harvest Moon glow from dusk to dawn, it does so for several nights both before and after full. The time between moonrise night to night shifts with the seasons from as much as 50 minutes in late winter to its current minimum of about 25 minutes.


Illustration: © Copyright 1925 M.C. Escher/Cordon Art-Baarn-Holland; Graphics: © Copyright 2007 Pacific Publishers. Reprinted by permission from the Tidelog graphic almanac. Bound copies of the annual Tidelog for Chesapeake Bay are $14.95 ppd. from Pacific Publishers, Box 480, Bolinas, CA 94924. Phone 415-868-2909. Weather affects tides. This information is believed to be reliable but no guarantee of accuracy is made by Bay Weekly or Pacific Publishers. The actual layout of Tidelog differs from that used in Bay Weekly. Tidelog graphics are repositioned to reflect Bay Weekly’s distribution cycle.Tides are based on National Oceanic and Atmospheric Administration and are positioned to coincide with high and low tides of Tidelog.

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