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Northern Crown

May 29, 2013

A pretty but faint semicircle of stars crowns the sky around midnight. Appropriately enough, it’s the constellation Corona Borealis — the northern crown.

Corona Borealis is one of the 48 constellations passed down to us from ancient times — from a catalog compiled by the astronomer Ptolemy almost 2,000 years ago. It represents the jeweled crown worn by Ariadne at her wedding to the god Dionysus. After the wedding, the exuberant god threw the crown into the sky, where its jewels formed a sparkling constellation.

Unfortunately, most of those starry jewels are pretty faint. Under dark skies, though, they’re fairly easy to pick out because of their eye-catching pattern.

The brightest member of the crown stands atop it. Alphecca is actually two stars, not one. The brighter of the two is pretty impressive — it’s several times bigger and heavier than the Sun, and dozens of times brighter. The other star is smaller and fainter than the Sun. It passes behind the big star once every 17.4 days, causing the system’s total brightness to drop by a few percent.

Some of the other stars in Corona Borealis also fade in and out — sometimes by quite a bit. But these light shows are much different from Alphecca’s. We’ll have more about a couple of those stars tomorrow.

In the meantime, look for the northern crown high in the east as night falls, and arching high overhead a few hours later — crowning the night sky with a ring of starry jewels.


Script by Damond Benningfield, Copyright 2013

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