145 Canis Majoris (h 3945 / Winter Albireo)
Coordinates, Gaia DR3 parallaxes of HD 56577 & HD 56578, 26.8″ orange-supergiant and blue-white optical pair, and guide for 145 CMa.
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 (HD 56577 primary) | 4.79 mag | ± 0.02 mag | Johnson UBV photometry (companion HD 56578 = 5.86 mag) | definitive | Hipparcos New Reduction Catalog |
| Visual A–B angular separation | 0.447 arcmin | ± 0.002 arcmin | WDS & Gaia DR3 astrometry (26.8 arcseconds at PA 50°) | definitive | ESA Gaia Archive — Data Release 3 |
| Distance to K3 Ib supergiant HD 56577 (Gaia DR3) | 870 pc | ± 45 pc | Gaia DR3 parallax of primary (1.15 ± 0.06 mas, ~2,840 ly; foreground B is at 105.7 ± 0.5 pc / 345 ly) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Primary effective temperature (HD 56577) | 4100 K | ± 100 K | K3 Ib supergiant spectroscopy (companion HD 56578 = 7,400 ± 150 K) | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Winter Albireo (145 Canis Majoris Double) at RA 07h 16m 35.27s, Dec -23° 18′ 51.8″ 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
145 Canis Majoris (Gould designation 145 CMa, cataloged by Sir John Herschel at the Cape of Good Hope in 1837 as h 3945) is universally known among amateur astronomers as 'the Winter Albireo.' Located in eastern Canis Major just 3.5° northeast of Wezen (Delta Canis Majoris), this 26.8-arcsecond pair rivals Cygnus's summer Albireo with one of the most saturated orange-gold and icy-blue color contrasts in the entire sky.
What makes 145 Canis Majoris a fascinating lesson in observational astrophysics is its three-dimensional cosmic perspective: while the two stars appear side-by-side in the eyepiece separated by just 26.8 arcseconds (with magnitudes 4.79 and 5.86), Gaia DR3 parallaxes prove that they are a pure line-of-sight optical double separated by 2,500 light-years of depth!
The fainter blue-white component, HD 56578 (magnitude 5.86, spectral class F0 V / A5m, 7,400 K), lies relatively close in the foreground at 105.7 ± 0.5 parsecs (345 light-years). Directly behind it at ~870 ± 45 parsecs (~2,840 light-years—more than eight times farther away!) sits HD 56577 (magnitude 4.79), a colossal K3 Ib orange-red supergiant spanning ~160 solar radii and shining with ~6,500 solar luminosities so that it outshines the foreground dwarf by a full magnitude across a 2,500-light-year gulf.
Practical Visual Observing Guide
- Easy to star-hop to in Canis Major: locate 1.8-magnitude Wezen (δ CMa) and sweep 3.5° northeast to the 3.0-magnitude blue supergiant Omicron² Canis Majoris (ο² CMa); 145 CMa sits just 1.3° north-northwest of ο² CMa.
- At 26.8 arcseconds separation along position angle 50°, any 50–80 mm telescope at 30×–60× splits 145 CMa into a deep tangerine-topaz ember and a contrasting cobalt-blue companion, all set inside a rich Milky Way starfield.
Catalog Cross-Identifications & Aliases
Common Aliases: 145 Canis Majoris · h 3945 · HD 56577 / HD 56578 · HIP 35210
| Catalog Authority | Identifier |
|---|---|
| GAIADR3 | 5617155966826356096 |
| HIP | HIP 35210 |
| HD | HD 56577 |
| SIMBAD | HD 56577 |
| WIKIDATA | Q2704225 |
Related Objects, Comparisons & Guides
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.
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.
Iota Cancri (Spring Albireo Color Double)
Coordinates, Gaia DR3 distance (330 ly), 30.7″ gold-and-blue double star (G8 Iab + A3 V), and observing guide for Iota Cancri.
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.
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.
Scientific Sources & Dataset Provenance
- 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
- 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