Jimmy Westlake: The bears are back
May 3, 2017
Steamboat Springs — No, not those bears. The celestial bears. The ones with the unnaturally long tails made of stars. You know — Ursa Major and Ursa Minor.
As my friend and poet laureate of the State of Georgia, the late Bettie Sellers, expressed in her famous poem, "Complaint to Betelgeuse."
"I used to know that stars were stars
and stayed wherever in that distant place
their ordered orbit was. The sky
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was snug with Cassiopeia’s Chair,
and night had Big and Little Bears to hunt."
The celestial bears are coming out of their winter hibernation and can be seen parading around the north celestial pole this month. Better known in the United States as the Big and Little Dippers, these star patterns are recognized and adored by all.
By 9:30 p.m. on early May evenings, the seven bright stars that form the Big Dipper shine prominently, high up overhead. In order, from tip to tail, the seven stars of the Big Dipper are named Dubhe, Merak, Phecda, Megrez, Alioth, Mizar and Alkaid.
Dubhe and Merak, the two stars at the end of the Big Dipper's bowl, are nicknamed "the Pointer Stars" because a line drawn through them and extended downward, like an arrow, will always lead you to the North Star, Polaris.
Polaris is as bright as the stars of the Big Dipper but is unique because it is the star that lies closest to the north pole of the sky — the north celestial pole. As the Earth spins on its axis, the sky appears to pivot around the north celestial pole with Polaris positioned at the center of the bull's eye. It remains nearly motionless in our sky all night long and can always be relied upon to show us the way north.
Polaris also happens to lie at the end of the handle of the star pattern we call the Little Dipper. Like the Big Dipper, the Little Dipper is composed of seven stars, but only three of the seven are easy to see: Polaris, Kochab, and Pherkad.
Moving down the handle from Polaris, the names of the remaining stars are Yildun, Epsilon, Zeta, Eta, Pherkad and Kochab. Kochab is nicknamed "the Guardian of the Pole" because it circles the pole star Polaris, as if protecting it from all harm.
Here are a few things about our Pole Star that maybe you didn't know:
Polaris is the closest pulsating Cepheid variable star to Earth. Stars like Polaris are well advanced in age and are going through a stage of instability, causing them to beat like a heart. Its brightness waxes and wanes by about 15 percent over a period of four days but this slight variability is not easily perceptible to the naked eye.
Polaris is also the brightest member in a trinary star system located 431 light years from Earth. In other words, what looks like a single star to the unaided eye is really three stars in an intricate dance with each other. One star orbits Polaris with a period of about 30 years, and the other takes thousands of years to complete its orbit.
Polaris has been known by many names down through the ages. Its current popular title comes from the Latin name "Stella Polaris," meaning "Pole Star." Other names include Cynosura (the Dog's Tail), Lodestar, Navigatoria and Angel Stern (Angel Star).
Polaris has not always been our pole star. Thanks to the slow, 26,000-year wobble of the Earth on its axis, Polaris assumes the role of our pole star for only a few centuries every cycle before the axis wanders on to another pole star. Polaris will be closest to the pole of the sky in the year 2100, then, it will start moving away. Better enjoy it while it lasts.
If you have good vision, you can make out an eighth star in the Big Dipper, right beside Mizar, the star at the crook in the Dipper's handle. This little star is named Alcor. Mizar and Alcor have been known since antiquity as "the Horse and Rider" and were used as a test for keen eyesight.
In Great Britain, our Big Dipper is imagined to be "Charlemagne's Wagon." Mizar is the middle horse pulling the wagon, and little Alcor is popularly known as "Jack on the Middle Horse." So, our rider has a name — it's Jack.
My favorite story about Alcor comes to us from Viking mythology. To the Norsemen, our constellation of Orion the Hunter was Orwandil the Giant.
One day, when Orwandil was crying like a big baby because his toe was frostbitten, the god Thor grew tired of his whining and snapped off the frozen toe. Yee-ouch! He then threw the toe into the northern sky where we can see it shining tonight as our little star Alcor, right beside Mizar.
Jimmy Westlake retires this month from Colorado Mountain College, after 19 years as its professor of physical sciences, and he is looking forward to spending a lot more time under the starry sky. His “Celestial News” column appears monthly in the Steamboat Today newspaper. Check out Jimmy's astrophotography website at jwestlake.com.
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