Alphecca (Alpha Coronae Borealis)
Alphecca (Alpha Coronae Borealis) is a star in the constellation Corona Borealis, magnitude 2.2.
The jewel of the Northern Crown — two stars that take turns hiding each other every 17 days.
Alphecca is the bright gem in a small arc of stars, the Northern Crown. Its Arabic name is short for nayyir al-fakka, “the bright one of the broken ring”; in Latin it was Gemma, “jewel”. In one myth the crown is Ariadne’s wedding diadem, and a Latin name drawn from Virgil’s Georgics, Gnosia Stella Coronae, recalls her home at Knossos on Crete.
It is really two stars, circling every 17.4 days in an orbit we see almost exactly edge-on, so each takes a turn passing in front of the other. That makes it an eclipsing binary like Algol, though the dimming is far subtler. The main star is white, about 2.6 times the Sun’s mass; its partner is a yellow star slightly smaller than the Sun.
That small partner is fierce: it gives out 30 times the Sun’s peak X-ray output, as expected for a young star. Around the white star, extra infrared light reveals a disc of dust, perhaps a planetary system in the making, like the one thought to surround Vega.
Alphecca (Alpha Coronae Borealis) is 75 light-years away: the light we see from it set off in 1951, 6 years before Sputnik became the first artificial satellite.
Did you know?
- A Behenian star. Under the name Alphecca it was one of the Behenian fixed stars, a short list of stars prized by medieval astrologers.
- Namesake in the south. As the brightest star of the Northern Crown, it lent its name to Alphekka Meridiana, the brightest star of the Southern Crown.
- Family ties. Alphecca moves through space with the Ursa Major Moving Group, a loose family of stars sharing a common motion.
A white 2nd-magnitude star, the bright gem in the small semicircle of the Northern Crown, east-north-east of Arcturus. Binoculars frame the whole crown; its eclipses are too slight to see by eye.
When and where to see it
It is best placed in the evening sky around June, when it crosses the meridian at about 10 pm local time (around midnight in May). It can be seen from everywhere north of 63°S and never sets north of 63°N.
At its highest it stands 67° up from 50°N, 82° up from 35°N, 63° up from the equator, 28° up from 35°S.
Facts
- Type
- Star
- Constellation
- Corona Borealis
- Designations
- Alpha Coronae Borealis, α CrB, 5 CrB, HR 5793, HD 139006, HIP 76267
- Magnitude
- 2.2
- Position
- RA 15h 34.7m, Dec +26° 43′ (J2000)
- Spectral type
- A1IV
- Colour
- white (B−V -0.02)
- Distance
- 75 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Alphecca (Alpha Coronae Borealis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.