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Volume xviii, Issue 10 ~ March 11 - March 17, 2010

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Sky Watch

by J. Alex Knoll

Stopped Cold In Its Tracks

Watch over the coming weeks as Mars makes
an about-face

The waning crescent moon rises a little before 5am Friday, climbing 20 degrees before sunrise at 6:22. Saturday morning, the moon rises 40 minutes later while the quickening sun rises two minutes earlier. By Sunday, only the thinnest sliver of moon remains, rising less than 45 minutes before the sun. If you’re lucky enough to see this slim crescent, look for Jupiter a few degrees to the moon’s back, the eastern side of its illuminated curve.

By Monday, the new moon is obscured in the sun’s glare. But come Tuesday, a nascent moon emerges, visible low in the west just after sunset, although you may need binoculars to spot it. The narrow crescent again has a neighbor, this time dazzling Venus a few degrees higher, and Wednesday evening a few degrees lower.

While Jupiter rules from the edge of twilight and Venus dominates in daybreak’s approach, Mars fills the hours in between, the brightest remaining light other than Sirius to the south. The red planet is high in the east at dusk and directly overhead at 9pm, 10pm after Sunday’s switch to Daylight Savings Time.

For the past several months, Mars has appeared night by night to move backward — to the west — against the stellar background. Thursday, March 11, the red planet stops in its tracks, and then returns to the typical eastward movement through the heavens.

Of course, Mars isn’t changing direction, but it wasn’t until the 1500s that Nicolaus Copernicus explained this in his treatise, On the Revolutions of the Celestial Spheres. The apparent planetary motion is caused by the orbital movement of earth in relation to that of the other planets, much like a fast-moving car passing a slow-moving one causes the slower one to appear to move backward in the rear-view mirror.

Illustration: © Copyright 1925 M.C. Escher/Cordon Art-Baarn-Holland; Graphics: © Copyright 2010 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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