Jimmy Westlake: Northern crown adorns summer sky
June 10, 2014
Steamboat Springs — One of the smallest of our 88 constellations shines down on us in the late spring and early summer. It's not particularly bright, but its distinctive shape makes it a favorite among sky watchers. It represents the golden, star-studded crown of Greek Princess Ariadne and is known as our constellation of Corona Borealis, the Northern Crown.
To locate Corona Borealis, look high up in the eastern sky after darkness falls for a small half-circle of stars, like a letter "C." It's about a third of the way from the bright star Arcturus toward the comparably bright star Vega to the east.
A person with normal vision should be able to see seven glittering stars outlining the celestial crown. The brightest of the seven is a star known by two different names, Alphecca, meaning "the broken circle,” and Gemma, meaning "the jewel of the crown."
I have a childhood memory of this delightful little constellation. I can remember being outside with my mother one warm Georgia night, looking up at the amazing star-filled sky while the lightening bugs flashed off and on around us.
Even at the age of 5, I was a budding astronomer. Not really knowing what I was looking at, I pointed out the C-shaped pattern of Corona Borealis and speculated to my mother that the brightest star was probably a sun, like ours, and the other bright stars in the "C" were planets orbiting around that sun. It was some years later when I realized that what I had seen was really the Northern Crown with its bright star Gemma.
Corona Borealis has within its borders one of the most unusual stars known, a "reverse nova" named R Coronae Borealis, or R Cor Bor. An ordinary nova suddenly increases in brightness when it erupts, but a reverse nova does just the opposite. Normally, a sixth magnitude star, just at the limit of naked-eye visibility, R Cor Bor will occasionally fade to only 1/1,600th its normal brightness before slowly recovering.
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Astronomers believe that this peculiar behavior is due to the formation of carbon soot in the cool star's atmosphere. R Coronae Borealis bears constant watching since its light variations are completely unpredictable. Its most recent episode of dimming happened in the spring of 2003.
You can find it with binoculars near the center of the "C" pattern of Ariadne's crown.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy's astrophotography website at http://www.jwestlake.com.
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