What kind of star is Alphecca?
Alphecca, catalogued as Alpha Coronae Borealis A (α CrB A), appears in the official constellation Corona Borealis. Its apparent visual magnitude is about 2.22; shallow eclipses, while its estimated distance is about 75 light-years. Astronomers classify the object as A0 V + G5 V eclipsing binary. These labels describe temperature, luminosity class or system components; they should not be read as a claim that every naked-eye point is a single isolated star.
Alphecca’s two stars orbit in a period of about 17.36 days. The brighter A-type primary dominates visible light, while a cooler G-type companion contributes much less; their geometry produces shallow eclipses rather than Algol’s dramatic changes. Infrared excess around the system has been interpreted as circumstellar or circumbinary debris, though its detailed architecture is model-dependent. Because the binary’s orbital plane and the primary’s rotation can be compared, Alphecca also informs studies of alignment in close binaries. It is nearby enough for precise orbital and stellar-parameter work across several observing techniques.
The coordinate pair RA 15h 34m 41.27s, Dec +26° 42′ 52.9″ fixes the object's direction on the celestial sphere for the J2000 reference epoch. Right ascension works like celestial longitude measured in hours, while declination works like latitude north or south of the celestial equator. Proper motion and improved measurements can refine catalogue positions, but these coordinates are sufficiently precise for a finder chart or planetarium search.
Alphecca data at a glance
| Proper name | Alphecca | Catalogue designation | Alpha Coronae Borealis A (α CrB A) |
|---|---|---|---|
| Constellation | Corona Borealis | Apparent magnitude | about 2.22; shallow eclipses |
| Spectral or system type | A0 V + G5 V eclipsing binary | Estimated distance | about 75 light-years |
| Right ascension (J2000) | 15h 34m 41.27s | Declination (J2000) | +26° 42′ 52.9″ |
Values are rounded for an observer-friendly overview. Consult the linked SIMBAD record for component-level identifiers, bibliography, measurement provenance and newer catalogue values.
The name Alphecca
Alphecca comes from Arabic nayyir al-fakka, “the bright one of the broken ring.” Gemma, Latin for “jewel,” is a longstanding alternative name.
The classical crown was described as a broken or open ring in Arabic naming, with Alphecca singled out as its bright member. The alternative Gemma casts it as the crown’s gemstone. Bayer designated it Alpha Coronae Borealis, and later photometry established that its light varies during eclipses. Modern IAU standardization chose Alphecca as the official proper name, while Gemma remains useful historical context rather than a second formal identity.
Modern professional catalogues retain identifiers such as the Bayer designation alongside a proper name. The International Astronomical Union standardizes which name belongs to which component—an important distinction for systems whose combined light looks like one star from Earth.
How to find Alphecca
First locate Arcturus, then move east toward Hercules for a compact semicircle of stars. Alphecca is the ring’s bright central jewel. The binary’s small eclipse is better recorded with calibrated photometry than judged by casual naked-eye comparison.
A northern-sky star best seen on late-spring and summer evenings; visible from most inhabited southern latitudes too. Visibility on a particular night still depends on latitude, season, time, horizon obstructions, weather and local light pollution. Use the interactive atlas below to check the surrounding field before observing.
Observation checklist
- Look east of Boötes for a small, tidy semicircle rather than a large constellation.
- Alphecca is immediately obvious as the brightest point in the crown.
- Use binoculars to trace the complete arc under suburban skies.
- To detect the eclipse, take repeated standardized brightness measurements over several weeks.
Interesting facts about Alphecca
- Alphecca’s alternative traditional name is Gemma, the jewel.
- The system is an eclipsing binary with an orbit of about 17.36 days.
- Its primary is an A-type star and its companion resembles a somewhat cooler Sun-like star.
- The eclipses are much shallower than Algol’s.
- Infrared measurements suggest debris associated with the system.
Continue from Alphecca into the night sky
Use the Corona Borealis constellation guide to place this star within its larger pattern. When you are ready to observe, compare dark-sky places, find a nearby observatory, or follow our practical guide to finding a star in the night sky. Symbolically registered names are kept separately in the searchable Star-Register catalogue.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values. Survey panels show photographic sky fields, not the physical surface of the star.