Cor Caroli (Alpha Canum Venaticorum / α² & α¹ CVn)
Coordinates, Hipparcos distance (115 ly), 19.3″ double star, 5.47-day magnetic Ap prototype α² CVn, and observing guide for Cor Caroli.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Apparent visual magnitude (α² CVn primary) | 2.89 mag | ± 0.03 mag | Johnson UBV photometry (rotational variation 2.84–2.98 mag; companion α¹ CVn = 5.60 mag) | definitive | Hipparcos New Reduction Catalog |
| Trigonometric parallax | 28.39 mas | ± 0.25 mas | Hipparcos New Reduction + Gaia DR3 (35.22 ± 0.31 pc / 114.9 ly) (J2000.0) | definitive | Hipparcos New Reduction Catalog |
| Visual α²–α¹ angular separation | 0.322 arcmin | ± 0.002 arcmin | WDS astrometry (19.3 arcseconds at PA 229°; ~680 AU projected) | definitive | ESA Gaia Archive — Data Release 3 |
| Magnetic rotation period of α² CVn | 5.46939 d | ± 0.00002 d | Zeeman-Doppler magnetic & photometric modulation | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Cor Caroli (Alpha Canum Venaticorum Double) at RA 12h 56m 01.67s, Dec +38° 19′ 06.2″ within Canes Venatici, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Cor Caroli (Alpha Canum Venaticorum, Latin for 'the Heart of Charles'—named in the 17th century by Sir Charles Scarborough and Edmond Halley in honor of King Charles I of England) is the brightest star in Canes Venatici (the Hunting Dogs) and the southern anchor of the 'Diamond of Virgo' asterism alongside Arcturus, Spica, and Denebola. Located 35.22 ± 0.31 parsecs (114.9 light-years) from Earth, it is one of the finest wide double stars in the spring sky.
Separated by 19.3 arcseconds along position angle 229° (~680 AU in space), the binary consists of magnitude 2.89 α² Canum Venaticorum (a 2.97-solar-mass, 11,600 K A0p star) and magnitude 5.60 α¹ Canum Venaticorum (a 1.47-solar-mass, 7,000 K F0 V main-sequence star that is itself a 51.6-day spectroscopic binary). Because their orbital period is nearly 9,000 years, their separation and position angle have remained virtually frozen since Robert Hooke first split them in 1664.
In astrophysics, the brighter star α² CVn is the namesake prototype of the Alpha² Canum Venaticorum variable stars: possessing a fossil dipolar magnetic field of ~1,500 to 5,000 Gauss—more than a thousand times stronger than the Sun's global field—its magnetic poles concentrate vast chemical starspots of silicon, chromium, europium, and mercury up to 10,000 times solar abundance. As the star rotates every 5.469 days, these magnetic element patches sweep across our view, varying its brightness between magnitude 2.84 and 2.98.
Practical Visual Observing Guide
- Located 14° south of Alkaid and Mizar beneath the arc of the Big Dipper's handle.
- At 19.3 arcseconds separation, Cor Caroli splits effortlessly in any 40–60 mm refractor at 30×–60× (or steadily mounted 15×70 binoculars), showing a sparkling blue-white primary paired with a warm yellowish-fawn or pale lilac secondary.
Catalog Cross-Identifications & Aliases
Common Aliases: α Canum Venaticorum · α² & α¹ CVn · HD 112413 / HD 112412 · HIP 63125 · 12 Canum Venaticorum
| Catalog Authority | Identifier |
|---|---|
| HIP | HIP 63125 |
| HD | HD 112413 |
| SIMBAD | * alf02 CVn |
| WIKIDATA | Q13050 |
Related Objects, Comparisons & Guides
Alioth (Epsilon Ursae Majoris Ap Variable)
Coordinates, Hipparcos distance (82.6 ly), magnitude 1.77, Alpha2 CVn magnetic chromium spots, and observing guide for Alioth in Ursa Major.
Mizar & Alcor (Zeta Ursae Majoris System)
Coordinates, Hipparcos/VLBI distance (82.8 ly), 11.8′ naked-eye pair, 14.4″ Mizar A–B split, and observing guide for Mizar & Alcor.
Albireo (Beta Cygni Color Double Star)
Coordinates, Gaia DR3 parallaxes of Beta Cygni A & B, 34.6″ angular separation, color contrast, and observing guide for Albireo in Cygnus.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Stellar Spectral Classification (OBAFGKM)
Reference guide to Morgan-Keenan (MK) stellar classification (O B A F G K M), luminosity classes (I–V, WD), color index (B-V), and the H-R diagram.
Scientific Sources & Dataset Provenance
- Hipparcos New Reduction Catalog (2007 New Reduction): van Leeuwen, F. 2007, A&A, 474, 653 (Validation of the new Hipparcos reduction) — ESA / van Leeuwen (2007)
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg