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Volume 15, Issue 15 ~ April 12 - April 18, 2007

The Celestial Compass

Let the Big Dipper guide you through the heavens

While the Big Dipper is not even a constellation, rather an asterism, a segment of the Great Bear Ursa Major, it is easily the most recognized shape in our night sky. For the next few weeks it’s directly overhead from sunset to midnight. Looking beyond the Dipper’s familiar outline, it’s also a guide to the universe beyond.

The star at the lip of the Dipper, Dubhe, and that beneath it, Merak, are called the pointer stars, pointing to Polaris, the North Star within the Little Bear Ursa Minor, commonly called the Little Dipper.

From the Big Dipper’s curved handle, follow the stars Alioth, Mizar and Alkaid, then arc to Arcturus, the red giant of Boötes the herdsman or bearkeeper and fourth brightest of all stars, dimmer than only Sirius in the Northern Hemisphere. Drop from Arcturus and spike to Spica, the blue-white shaft of wheat held outstretched in the hand of Virgo.

A small telescope or even strong binoculars will reveal two distant galaxies to either side of the Dipper’s last handle star, Alkaid. They may not look like much, small blotches of light as opposed to the piercing light of a star, but the Pinwheel Galaxy (M33) and the Whirlpool Galaxy (M51) take you through the cosmos. While the two appear equally faint, they are far from similar. At 50,000 light years across, the Pinwheel is about half the size of our own Milky Way, yet only 3 million light years away, it’s one of the nearest galaxies. The Whirlpool, a spiral galaxy like our own, is more than double the size of the Milky Way and more than 31 million light years distant.


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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