Tau Canis Majoris
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Canis Major |
| Right ascension | 07h 18m 42.48642s |
| Declination | −24° 57′ 15.7413″ |
| Apparent magnitude (V) | 4.40 4.89 (Aa) 5.33 (Ab) 9.70 (E) |
| Characteristics | |
| Spectral type | OC8.5 Ib((f)) (Aa1) B0:nn (Aa2a/b) O9.2 II (Ab) |
| U−B color index | −0.99 |
| B−V color index | −0.15 |
| Variable type | β Lyr (Aa2) |
| Astrometry | |
| Radial velocity (Rv) | +33.80 km/s |
| Proper motion (μ) | RA: −2.31 mas/yr Dec.: +5.02 mas/yr |
| Parallax (π) | 1.09±0.59 mas |
| Distance | 4,900+390 −360 ly (1,500+120 −110 pc) |
| Absolute magnitude (MV) | −5.6 |
| Orbit | |
| Primary | τ CMa Aa |
| Name | τ CMa Ab |
| Period (P) | 306.8–408.7 years |
| Semi-major axis (a) | 174.1–198.8 mas |
| Inclination (i) | 81.7–82.5° |
| Longitude of the node (Ω) | 297.5–298.9° |
| Periastron epoch (T) | 1949.3–1970.4 |
| Semi-amplitude (K1) (primary) | 17.6–20.5 km/s |
| Orbit | |
| Primary | τ CMa Aa1 |
| Name | τ CMa Aa2 |
| Period (P) | 154.900±0.004 days |
| Eccentricity (e) | 0.280±0.005 |
| Inclination (i) | near 90° |
| Periastron epoch (T) | 2,455,098.3±0.4 |
| Argument of periastron (ω) (secondary) | 84.3±1.1° |
| Semi-amplitude (K1) (primary) | 87.0±0.5 km/s |
| Orbit | |
| Primary | τ CMa Aa2a |
| Name | τ CMa Aa2b |
| Period (P) | 1.282 days |
| Position (relative to A) | |
| Component | E |
| Epoch of observation | 2018 |
| Angular distance | 0.90″ |
| Position angle | 87° |
| Details | |
| τ CMa Aa1 | |
| Mass | 30 M☉ |
| Radius | 17.7 R☉ |
| Luminosity | 280,000 L☉ |
| Surface gravity (log g) | 3.37 cgs |
| Temperature | 32,514 K |
| Rotational velocity (v sin i) | 90 km/s |
| Age | 3.4 Myr |
| τ CMa Aa2a | |
| Mass | 19 M☉ |
| τ CMa Aa2b | |
| Mass | 19 M☉ |
| τ CMa Ab | |
| Mass | 25±5 M☉ |
| Other designations | |
| τ Canis Majoris, 30 Canis Majoris, CD−24°5176, GC 9736, HD 57061, HIP 35415, HR 2782, SAO 173446, ADS 5977, CCDM 07187-2457 | |
| Database references | |
| A | |
| SIMBAD | data |
Tau Canis Majoris is a multiple star system in the constellation Canis Major, consisting of five stars. Its name is a Bayer designation that is Latinized from τ Canis Majoris, and abbreviated Tau CMa or τ CMa. This system is approximately 5,000 light years distant from Earth and is the brightest member of the open cluster NGC 2362.
This star is sometimes known as the 'Mexican Jumping Star' by amateur astronomers, because it can appear to 'jump around' with respect to the other stars in the cluster because of its marked contrast in brightness.