Sirius (Alpha Canis Majoris)
Coordinates, Hipparcos parallax (379.21 mas, 8.60 ly), magnitude −1.46, Sirius B white dwarf orbit, and observing guide for Sirius.
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 (Sirius A) | -1.46 mag | ± 0.01 mag | Johnson UBV photoelectric photometry (J2000.0) | definitive | Hipparcos New Reduction Catalog |
| Trigonometric parallax | 379.21 mas | ± 1.58 mas | Hipparcos New Reduction astrometric solution (J2000.0) | definitive | Hipparcos New Reduction Catalog |
| Distance in light-years | 8.6 ly | ± 0.04 ly | Derived from parallax 379.21 ± 1.58 mas (2.637 ± 0.011 pc) | definitive | Hipparcos New Reduction Catalog |
| Primary mass (Sirius A) | 2.063 M☉ | ± 0.023 M☉ | HST astrometric binary orbit (Bond et al. 2017) | definitive | SIMBAD Astronomical Database (CDS) |
| Bolometric luminosity (Sirius A) | 25.4 L☉ | ± 1.3 L☉ | Interferometric angular diameter + bolometric flux | high-confidence | SIMBAD Astronomical Database (CDS) |
| Effective temperature (Sirius A) | 9940 K | ± 210 K | High-resolution spectroscopy & long-baseline interferometry | high-confidence | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Sirius (Alpha Canis Majoris Binary) at RA 06h 45m 08.92s, Dec -16° 42′ 58.0″ 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
Sirius (Alpha Canis Majoris, the 'Dog Star') is the brightest star in Earth's night sky at apparent visual magnitude −1.46—nearly twice as bright as second-place Canopus. Its brilliance stems from both intrinsic luminosity (25.4 solar luminosities from a 2.06-solar-mass A0mA1 Va main-sequence star) and close proximity: at just 2.637 ± 0.011 parsecs (8.60 light-years), Sirius is the fifth-nearest stellar system to the Sun.
In 1844 Friedrich Bessel deduced from periodic wobbles in Sirius's proper motion that it must be orbited by an unseen companion, and in January 1862 telescope maker Alvan Graham Clark visually discovered Sirius B ('the Pup'). Orbiting with a period of 50.13 years and an eccentricity of 0.591, Sirius B is a dense carbon-oxygen DA2 white dwarf packing 1.018 ± 0.011 solar masses into a sphere the size of Earth (radius 0.0084 solar radii).
Approximately 120 million years ago, Sirius B was a ~5-solar-mass B-type star that evolved through its asymptotic giant branch phase and transferred mass onto Sirius A before shedding its outer envelope—enriching Sirius A's photosphere with excess iron and barium and turning it into a metallic-line Am star.
Practical Visual Observing Guide
- Follow the three stars of Orion's Belt ~20° southeast to land directly on Sirius, which scintillates in vivid flashes of blue, white, emerald, and crimson when low on the winter horizon.
- Splitting magnitude 8.44 Sirius B ('the Pup') from magnitude −1.46 Sirius A (a 9.9-magnitude / 9,100:1 brightness contrast) is one of visual astronomy's classic tests: during the 2020s near apastron, their angular separation is widest (~10.5″ to 11.3″ at position angle ~60°–70°).
- Use a well-collimated 100–200 mm refractor or reflector at 200×–300× on a night of calm, laminar atmospheric seeing near meridian transit—or observe during twilight to reduce glare from Sirius A.
Catalog Cross-Identifications & Aliases
Common Aliases: α Canis Majoris · Sirius A & B · HD 48915 · HIP 32349
| Catalog Authority | Identifier |
|---|---|
| HIP | HIP 32349 |
| HD | HD 48915 |
| SIMBAD | * alf CMa |
| WIKIDATA | Q3409 |
Related Objects, Comparisons & Guides
Proxima Centauri (Nearest Star to Sun)
Coordinates, Gaia DR3 parallax (768.07 mas, 4.2465 ly), magnitude 11.13, flare activity, and planetary system guide for Proxima Centauri.
Rigel (Beta Orionis Blue Supergiant)
Coordinates, Hipparcos distance (264 pc), luminosity (120,000 L☉), Rigel BC companion, and observing guide for Rigel in Orion.
Betelgeuse (Alpha Orionis Red Supergiant)
Coordinates, competing optical vs radio distances (168 vs 222 pc), radius, Great Dimming physics, and observing guide for Betelgeuse.
Sirius A & B vs Vega A-Star Comparison
Compare the Sirius A/B binary system (A1 V main-sequence star + DA2 white dwarf at 2.64 pc) against zero-point A0 V standard Vega (at 7.68 pc).
Winter Circle, Orion & Taurus Observing Guide
Winter sky observing tour of Orion, Taurus, Canis Major, Auriga, and Perseus: bright OB/M supergiants, open clusters, M42, and the Crab Nebula (M1).
Splitting Bright Double & Multiple Stars Guide
How to resolve showcase binary and multiple star systems—Albireo, Mizar & Alcor, Epsilon Lyrae, Castor, and Sirius B—and test telescope Dawes limit.
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.
Trigonometric Parallax, Parsecs & Gaia DR3
How trigonometric parallax (d_pc = 1 / p_arcsec), the distance modulus equation, Hipparcos, and Gaia DR3 microarcsecond astrometry measure cosmic distances.
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.
Bright, Multiple & Variable Stars Catalog
Cross-reference catalog of solar-neighborhood and navigation stars across Bayer, Henry Draper (HD), Hipparcos (HIP), WDS, and Gaia DR3 designations.
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)
- IAU Working Group on Star Names (WGSN) (2026 IAU WGSN Bulletin): Mamajek, E., et al. (IAU WGSN) 2016–2026, IAU Catalog of Star Names — International Astronomical Union
- 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