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Volume 15, Issue 29 ~ July 19 - July 25, 2007

Breaking from the Sun

At its elongation this week, Mercury doubles in brightness

The waxing moon shines in the southeast at sunset, around 8:30 this week, each night appearing farther south and setting one-half hour later. Saturday’s first-quarter moon travels with Spica, the brilliant blue-white star in Virgo. Tuesday and Wednesday night, the moon forms a triangle with Jupiter and Antares, the red-orange heart of Scorpius; Tuesday the moon is 10 degrees to their west, Wednesday 10 degrees to their east.

Evening twilight has nearly obscured Saturn and Venus low in the west. Both set well before 10pm, first the ringed planet, then the evening star.

As darkness deepens, Jupiter rules from high in the south, with dimmer Antares not five degrees lower. The two remain tight throughout summer, now arcing across the southern sky and setting in the southwest before 2am.

As Jupiter sets at one edge of the sky, Mars rises at the opposite and has climbed high in the east by dawn. Currently, Mars is dim, standing out amid a dim backdrop of stars more for his steady glow than for its brightness. But between now and the end of the year, the red planet zooms closer to earth, growing brighter all the while and doubling in size.

You don’t have to wait to watch Mercury come into its glory. Not two months ago, Mercury glimmered in the west at dusk. Already this swift planet has swung around to the other side of the sun and appears in the east before dawn. Friday marks its greatest elongation, the farthest point from the sun, in this case at 20 degrees to the west.

Approaching elongation, Mercury more than doubles in brightness, outshining all stars at magnitude +0.3. Look for it an hour before sunrise, around 6am, above the east-northeast horizon.


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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