Adhara (Epsilon Canis Majoris)
Coordinates, Hipparcos distance (430 ly), magnitude 1.50, peak extreme-UV sky irradiance, 7.5″ companion, and observing guide for Adhara.
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 (V) | 1.5 mag | ± 0.01 mag | Johnson UBV photoelectric photometry | definitive | Hipparcos New Reduction Catalog |
| Trigonometric parallax | 8.05 mas | ± 0.14 mas | Hipparcos New Reduction astrometric solution (124.2 ± 2.2 pc) (J2000.0) | definitive | Hipparcos New Reduction Catalog |
| Distance in light-years | 405.2 ly | ± 7 ly | Derived from Hipparcos parallax 8.05 ± 0.14 mas | high-confidence | Hipparcos New Reduction Catalog |
| Bolometric luminosity | 38700 L☉ | ± 3200 L☉ | Extreme-UV / UV spectrophotometry + interferometric angular diameter (0.80 mas) | high-confidence | SIMBAD Astronomical Database (CDS) |
| Effective temperature | 22200 K | ± 400 K | EUVE & IUE ultraviolet continuum and line modeling | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Adhara (Epsilon Canis Majoris Extreme-UV Star) at RA 06h 58m 37.55s, Dec -28° 58′ 19.5″ within Canis Major, 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
Adhara (Epsilon Canis Majoris, from the Arabic al-ʿAdhārā meaning 'the Maidens') is the second-brightest star in Canis Major and the twenty-second brightest star in the night sky at apparent visual magnitude 1.50 (missed being designated a traditional 'first-magnitude' star by just 0.01 magnitudes). Located 124.2 ± 2.2 parsecs (405 light-years) away, Adhara is a massive B2 II blue-white bright giant of ~12.6 solar masses and 13.9 solar radii.
Observations by NASA's Extreme Ultraviolet Explorer (EUVE) space telescope revealed a remarkable astrophysical fact: at wavelengths between 500 and 900 Ångströms, Adhara is by far the brightest source of extreme-ultraviolet (EUV) radiation in the entire night sky—surpassing even the Sun at certain EUV lines as seen from outside the heliosphere! This occurs because Adhara's 22,200 K photosphere shines directly down a 300-light-year tunnel of hot, rarefied plasma in the Local Bubble almost completely devoid of neutral hydrogen gas, making Adhara the dominant ionizing source of the local interstellar cloud surrounding our Solar System.
Kinematic reconstruction of Adhara's radial velocity (+27.3 km/s) and proper motion shows that ~4.7 million years ago, Adhara passed within just 34 light-years of the Sun. At that epoch, its 38,700-solar-luminosity beacon blazed in Earth's Pliocene sky at apparent visual magnitude −3.99—nearly as bright as Venus at maximum brilliancy and seven times brighter than Sirius is today!
Practical Visual Observing Guide
- Marks the right hind leg of the Great Dog ~13° south-southeast of Sirius, forming a bright southern triangle with Wezen (δ CMa) and Aludra (η CMa).
- Adhara is a challenging visual binary: a 7.4-magnitude companion (Adhara B) sits 7.5 arcseconds southeast at position angle 161°, requiring a well-collimated 75–100 mm telescope at 150×–200× to split from the glare of the 1.5-magnitude primary.
Catalog Cross-Identifications & Aliases
Common Aliases: ε Canis Majoris · HD 52089 · HIP 33579 · 21 Canis Majoris
| Catalog Authority | Identifier |
|---|---|
| HIP | HIP 33579 |
| HD | HD 52089 |
| SIMBAD | * eps CMa |
| WIKIDATA | Q13038 |
Related Objects, Comparisons & Guides
Sirius (Alpha Canis Majoris Binary)
Coordinates, Hipparcos parallax (379.21 mas, 8.60 ly), magnitude −1.46, Sirius B white dwarf orbit, and observing guide for Sirius.
Wezen (Delta Canis Majoris Yellow Supergiant)
Coordinates, distance (~1,600 ly), magnitude 1.83, 215 R☉ yellow-white supergiant radius, and observing guide for Wezen in Canis Major.
Rigel (Beta Orionis Blue Supergiant)
Coordinates, Hipparcos distance (264 pc), luminosity (120,000 L☉), Rigel BC companion, and observing guide for Rigel in Orion.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Proper Motion, Radial Velocity & Redshift
How astronomers combine tangential proper motion (mas/yr), Doppler radial velocity (km/s), and cosmological redshift (z) to reconstruct 3D space motion.
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)
- 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