Topic of the month: Corona Borealis

The summer night sky brings a small constellation to the northern sky, Corona Borealis, the northern crown. It has no first magnitude stars, in fact most members of this constellation are third magnitude stars but its distinct curved pattern was noted by many cultures. The Greeks called it the Crown of Ariadne, the crown that Bacchus gave to his wife Ariadne and placed it in the heavens after she died. The Australian aborigines called it a boomerang, the Greeks saw it as a laurel wreath. This small constellation of stars can be seen in the summer nights between the constellations of Boötes and Hercules. The Welsh called it "Caer Arianrhod," the Castle of the Silver Circle that was the heavenly home of Lady Arianrod.

The Shawnee Indians also had a special myth about Corona Borealis, they called the constellation "The Celestial Sisters". In this legend twelve beautiful maidens came down from the sky in a silver basket to dance and sing. One night they were seen by a mighty hunter named "White Hawk", who tried to capture the youngest and most beautiful of the maidens, but they leaped back into the basket, and were instantly carried up into the sky. The next night White Hawk returned to the spot disguised as a field mouse. As the maidens danced, he resumed his form and succeeded in catching the youngest maiden and took her home as his bride. They lived together and soon they had a son. The maiden was still a member of the sky people and she became homesick. One day she made a silver basket, and singing a magic chant returned to the sky. She is thought to be the brightest star in the crown, second magnitude star Alphecca, also known as Gemma. White Hawk and his son were so sad after she left that the sky people took pity on them a brought them into the sky as well. White Hawk is thought to be represented by the the bright star, Arcturus, in the nearby constellation of Boötes.

The stars of Corona Borealis are readily visible to the naked eye at a dark site on a moonless night, however two members of the modern constellation are not often seen, but have an interesting history. They are variable stars. The first is T Coronae Borealis, also called "The Blaze Star. Normally, a star of 10th magnitude, the Blaze Star has shot up to a brightness that rivalled Gemma. Astronomers noted two occurrences, it reached 2.0 magnitude on May 12, 1866 and 3.0 magnitude on February 9, 1946. T Coronae Borealis is an aging red giant star approximately 2,000 light years away. The second star is R Coronae Borealis, a yellow supergiant star, that has been seen to fade by several magnitudes at irregular intervals. It normally shines around 6 magnitude but at irregular intervals (months or years) it may fade down to magnitude 14. It gradually returns to its normal brightness in a few months. This has earned the star its nickname of "Reverse Nova" or the "Fade-Out star." The star is considered to be a carbon star and it is thought that carbon builds up in the star's atmosphere, causing it to fade in brightness. The carbon gas is blown away eventually by the stellar wind or some other mechanism. The approximate position of these variable stars are noted on the finder chart as "R" and "T."

--See You Under the Stars!
Astra for Astra's Almanac