Volume 16, Issue 35 - August 28 - September 3, 2008

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Sky Watch by J. Alex Knoll

No Need to Fear that Ghostly Glow

It’s only the zodiacal light

Early risers up an hour before dawn Friday morning may catch a glimpse of the thin waning moon. The next morning, new moon rises and sets with the sun, not to escape its overpowering glare again until Monday, September 1, when a new waxing crescent appears low in the west-southwest at sunset, around 7:35.

If you can spot Monday’s thin crescent moon, you can see the twilight-bound planets Venus, Mercury and Mars. With no more than five degrees separating one from the other, the three planets form a wide isosceles triangle above the horizon. Venus easily outshines both Mercury — the next-brightest and nearest the horizon — and Mars — a pale reddish-orange blur higher above the horizon. On following nights, the moon moves up and on, but these three planets remain more or less fixed in place and time through the week.

Moonless late-summer nights reveal a faint, ghostly glow in the western sky after sunset. At first glimpse you may think your eyes are playing tricks on you. Look closer and you’ll discern a dim, pyramid-shaped patch of light stretching from west to south horizon.

This is the zodiacal light, caused by light from the already-set sun back-cast upon countless tiny particles of interplanetary dust. Some of these millimeter-sized particles date to the formation of our solar system; others are jetsam from asteroids or comets. While the interstellar wind scatters the smallest of these bits beyond our solar system, the sun’s gravity slowly pulls the others into orbit along the ecliptic, the imaginary line on which the sun, moon and planets appear to travel.


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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