42 Orionis
Star in the constellation of Orion
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42 Orionis, also known as c Orionis or c Ori, is a triple star system in the constellation Orion. Its apparent magnitude is 4.59[2] and it is approximately 900 light years away based on parallax.[1]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Orion |
| Right ascension | 05h 35m 23.16427s[1] |
| Declination | −04° 50′ 18.0881″[1] |
| Apparent magnitude (V) | 4.59[2] |
| Characteristics | |
| Spectral type | B1V[3] |
| U−B color index | −0.94[2] |
| B−V color index | −0.19[2] |
| Astrometry | |
| Radial velocity (Rv) | +28.40[4] km/s |
| Proper motion (μ) | RA: +4.52[1] mas/yr Dec.: −7.11[1] mas/yr |
| Parallax (π) | 3.69±1.20 mas[1] |
| Distance | approx. 900 ly (approx. 270 pc) |
| Orbit[5] | |
| Period (P) | 69.2 yr |
| Semi-major axis (a) | 0.146″ |
| Eccentricity (e) | 0.23 |
| Inclination (i) | 28.1° |
| Longitude of the node (Ω) | 125.4° |
| Periastron epoch (T) | 1986.4 |
| Argument of periastron (ω) (secondary) | 84.7° |
| Details | |
| Mass | 12.0[6] M☉ |
| Radius | 7.0[7] R☉ |
| Luminosity | 10,737[8] L☉ |
| Surface gravity (log g) | 3.82[7] cgs |
| Temperature | 25,400[8] K |
| Rotational velocity (v sin i) | 20[9] km/s |
| Age | 2.6[6] Myr |
| Other designations | |
| c Orionis, BD−04°1185, CCDM J05354-0450AB, GC 6934, HIP 26237, HR 1892, HD 37018, NSV 2318, SAO 132320, WDS J05354-0450AB | |
| Database references | |
| SIMBAD | data |
The primary star, Aa, has one spectroscopic companion Ab of magnitude 6.3 and separation 0.16", and a more distant companion B of 7.5 magnitude at 1.6" separation.[10][11] Preliminary results published in 2026 give an orbtal period of 69.2 years, an eccentricity of 0.23 and an inclination of 28.1° for the inner companion.[5]
42 Orionis is surrounded by NGC 1977 one of a smaller fainter group of named nebulae just north of the Orion Nebula. 42 Ori is the star which excites and illuminates NGC 1977.