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Big Dipper is heavenly signpost
This grouping of seven stars is only a small part of the Great Bear constellation

ANDREW S. FAZEKAS
Montreal Gazette

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click image to enlarge

Saturday, March 30, 2002 - Long before television, radio or the written word, our ancestors spent countless hours around fires telling tales of magical beasts and great hunts. Over the years, many of these legends were transposed into the night sky, familiar pictures scattered across the heavens.

Among all the star patterns, none is more engraved in human culture than the heavenly grouping of seven stars known as the Big Dipper. Never rising or setting below the horizon, it rotates around the North Star once every day. The Big Dipper is one of the first signposts we learn in our youth, helping us to navigate through the starry night to find the North Star.

Modern astronomers have officially recognized the dipper's stars as the tail of the Great Bear - the way the ancient Greeks, Germanic tribes and others saw them.

You might ask: When did anyone last see a bear with a long, bushy tail? The answer to this mystery lies in Greek mythology. According to legend, Zeus, the king of the gods, fell in love with a beautiful woman named Callisto. In an act of vengeance, Hera, the wife of Zeus, turned Callisto into a bear and set her up to be killed by her own son, who was a hunter. Just before the arrow could kill Callisto, Zeus grabbed her by the tail and swung her up to the safety of the sky, where she still lives. Being a heavy bear, her tail was stretched.

In springtime the Dipper, along with the entire Great Bear, turns upside down by mid-evening with the North Star below. Starting our tour of the Dipper, the stars that make up the bowl's outer edge are Dubhe and Merak, the famous "pointer" stars that guide stargazers to the North Star.  Continuing around in order, we pass Megrez, the faintest of the seven stars, Phecda, at the joint of the bowl and handle, and Alioth, Mizar and Alkaid, the three handle stars.

Unlike most constellations, where bright stars are unrelated to each other, five stellar members of the Big Dipper belong to the Ursa Major cluster - our nearest star cluster at about 80 light years distant. Born 150 million years ago from the same interstellar cloud, these stars are loosely bound together by gravity, traveling through the Milky Way galaxy in the same direction. The two outcasts are Dubhe and Alkaid, which appear to be drifting in the opposite path in space.   Over tens of thousands of years, the traditional dipper design will become distorted into an unrecognizable shape as these stars wander away from their stellar nursery.

By far the most celebrated star in this brotherhood of the bear is Mizar, the second one in the handle. Its claim to fame is its association to a much fainter companion star, Alcor. Known affectionately as the horse and rider, Mizar and Alcor are traditionally considered good tests for the naked eye and are eternal favourites for backyard astronomers with binoculars and telescopes. The ability to see Alcor was once an indication of keen vision and therefore a test for apprentice hunters. Ancient Arabs referred to it as "the Test" and "the Riddle." Can you see the pair on a clear moonless night?

Too far apart to be orbiting each other, Alcor's appearance close to Mizar is merely coincidental, making the stars an optical binary, separated by more than three light years. Pointing a small telescope at Mizar, however, will reveal a much closer, true companion. First sighted in 1650, this faint star orbits Mizar every 10,000 years. Detailed observations have indicated that Mizar might even be part of a remarkable quintuple star system, while little Alcor is a true binary in its own right.  No matter how long you've been stargazing, coming back to Mizar is always a treat.

While the southwest horizon is full of sparkling jewels that bedazzle us this season, riding high in the desolate northern skies finds the lonely Big Dipper and its parent constellation. For centuries it has been a celestial guidepost for humanity. With its splendid showing of bright and widely dispersed stars, the Great Bear is worth getting to know as it eternally guards the North Star.

- Andrew S. Fazekas's E-mail address is skyfeedback@hotmail.com.

 

Monthly highlights

-Tonight. Saturn, the second-largest planet, will glide north past the ruddy-coloured star Aldebaran in the constellation Taurus.

-Tuesday. A large crescent moon sits northwest of the bright orange star Antares of the Scorpius constellation in the predawn southern skies.

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-April 12. Within the new moon, this is the best time of the month to try and find the entire Ursa Major constellation in the moonless skies.

-April 16. Watch for a very thin crescent moon pairing up with Saturn at dusk in the western skies

.-April 18. Try catching a glimpse of Jupiter during the day. Track down the gas giant's shining light just below the crescent moon before sunset. Start your hunt at around 6 p.m. by spotting the moon first, high above the southwest skies. Binoculars will help you to track down Jupiter's bright white point of light.

-April 26. The full moon occurs at 11 p.m.

iIlustrations © Copyright 2002 Zoe Chee

Text © Copyright 2002 Andrew S. Fazekas
Copyright 2001 - 2002 Andrew Fazekas. All Rights Reserved. | modified September 20, 2002