Eta Orionis information

η Orionis
	Location of η Orionis (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Orion
Right ascension	05h 24m 28.61672s
Declination	–02° 23′ 49.7311″
Apparent magnitude (V)	3.42 (4.50 + 5.90 + 5.65 + 4.95)
Characteristics
Spectral type	Aa: B1 V; Ab: B3 V; Ac: B3 V; B: B2 V
U−B color index	–0.90
B−V color index	−0.17
Variable type	Algol
Astrometry
Radial velocity (Rv)	+19.8 km/s
Proper motion (μ)	RA: −0.71 mas/yr ; Dec.: −3.46 mas/yr
Parallax (π)	3.34 ± 1.07 mas
Distance	approx. 1,000 ly ; (approx. 300 pc)
Orbit
Primary	Aa
Companion	Ab
Period (P)	7.989255±0.000005 days
Eccentricity (e)	0.011±0.0002
Inclination (i)	85°
Semi-amplitude (K1); (primary)	145.5±0.03 km/s
Semi-amplitude (K2); (secondary)	150±3 km/s
Orbit
Companion	Ac
Period (P)	9.442±0.012 yr
Semi-major axis (a)	0.0441±0.0015″
Eccentricity (e)	0.45±0.02
Inclination (i)	102.8±1.8°
Details
η Ori Aa
Mass	11.0±0.5 M☉
Radius	6.3±0.6 R☉
Temperature	26,600 K
Rotational velocity (v sin i)	20 km/s
η Ori Ab
Mass	10.6±0.7 M☉
Radius	5.2±0.4 R☉
Temperature	26,600 K
Rotational velocity (v sin i)	130 km/s
η Ori Ac
Mass	6.78 M☉
η Ori B
Mass	8.7 M☉
Other designations
	η Ori, 28 Orionis, BD−02°1235, HD 35411, HIP 25281, HR 1788, SAO 132071
Database references
SIMBAD	data

Eta Orionis or Algjebbah, Latinized from η Orionis, is a multiple star in the constellation Orion. It lies a little to the west of Orion's Belt between Delta Orionis and Rigel, being closer to Delta Orionis than to Rigel. It lies at a distance of around 1,000 light-years from Earth and is part of the Orion OB1 association.

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Observation data Epoch J2000 Equinox J2000
Location of η Orionis (circled)
Constellation	Orion
Right ascension	05^h 24^m 28.61672^s^[1]
Declination	–02° 23′ 49.7311″^[1]
Apparent magnitude (V)	3.42^[2] (4.50 + 5.90 + 5.65 + 4.95)^[3]
Characteristics
Spectral type	Aa: B1 V Ab: B3 V Ac: B3 V B: B2 V^[3]
U−B color index	–0.90^[2]
B−V color index	−0.17^[2]
Variable type	Algol^[4]
Astrometry

Radial velocity (R_v)	+19.8^[5] km/s
Proper motion (μ)	RA: −0.71^[1] mas/yr Dec.: −3.46^[1] mas/yr
Parallax (π)	3.34 ± 1.07 mas^[1]
Distance	approx. 1,000 ly (approx. 300 pc)

Orbit^[6]
Primary	Aa
Companion	Ab
Period (P)	7.989255±0.000005 days
Eccentricity (e)	0.011±0.0002
Inclination (i)	85°
Semi-amplitude (K₁) (primary)	145.5±0.03 km/s
Semi-amplitude (K₂) (secondary)	150±3 km/s
Orbit^[3]
Companion	Ac
Period (P)	9.442±0.012 yr
Semi-major axis (a)	0.0441±0.0015″
Eccentricity (e)	0.45±0.02
Inclination (i)	102.8±1.8°
Details
η Ori Aa
Mass	11.0±0.5^[6] `M`_☉
Radius	6.3±0.6^[6] `R`_☉
Temperature	26,600^[6] K
Rotational velocity (v sin i)	20^[6] km/s
η Ori Ab
Mass	10.6±0.7^[6] `M`_☉
Radius	5.2±0.4^[6] `R`_☉
Temperature	26,600^[6] K
Rotational velocity (v sin i)	130^[6] km/s

η Ori Ac
Mass	6.78^[7] `M`_☉
η Ori B
Mass	8.7^[7] `M`_☉
Other designations
η Ori, 28 Orionis, BD−02°1235, HD 35411, HIP 25281, HR 1788, SAO 132071^[8]
Database references
SIMBAD	data

Eta Orionis information

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