Alphecca shines between summertime’s two most brilliant stars: Arcturus and Vega. An imaginary line drawn between these two brilliant beauties locates Alphecca every time, about one-third of the way from Arcturus to Vega. The other name for Alphecca – Gemma – means “gem” or “jewel.” On a dark night, this star certainly lives up to its name, sparkling at the forefront of the swirling semi-circle of stars that make up the constellation Corona Borealis, or the Northern Crown. In the lore of the skies, this C-shaped constellation represents the crown or wreath worn by the ancient Minoan Princess Ariadne.
As seen from mid-northern latitudes, Alphecca shines all night long – or nearly all night long – in April, May and June. Alphecca and this glittery bowl of stars crown the sky on July evenings, and continue to grace the heavens well into November. Starting around mid-November, Alphecca appears rather low in the west-northwest sky after dusk. It sets shortly after nightfall, then reappears in the east-northeast before dawn.
Jan Wojcik of Reynolds Observatory outlines Corona Borealis with green laser pointer; Photo credit: Kyle Foley
The Pleiades star cluster sits almost opposite Alphecca (and Corona Borealis) on the sky’s dome. Also starting in mid-November, the Pleiades cluster appears in the east-northeast after dusk, crosses the sky during the night, then gleams over the west-northwest sky before dawn. The Pleiades and Corona Borealis trade places in the sky after about 12 hours time. In later November, look for these two star formations at about 6 p.m. local clock time, then note that they have switched positions around 6 a.m. local clock time.
Pleiades: Famous Seven Sisters
Alphecca – like Algol in the constellation Perseus – is an eclipsing binary star. With a period of about 17.4 days, the fainter of Alphecca’s two component stars passes in front of the brighter one, resulting a slight dip in brightnesss. But Alphecca’s variation in brightness is barely perceptible, whereas Algol’s winking presence is easy to observe with just the naked eye.
