21 Orionis (HIP 24817)

21 Orionis is a yellow-white giant star in the constellation Orion. At 200 light years away, it shines at an apparent visual magnitude of 5.33. It is moving through the Galaxy at a speed of 16.4 km/s relative to the Sun.

Sky position: RA 5h 19.2m, Dec +2° 35.7'

Common designations: 21 Orionis, HR 1746, HD 34658, HIP 24817, Gaia DR3 3234497612436298752

21 Orionis has the spectral type F5III-IV. F-type stars are yellow-white stars of about 6,000 to 7,500 K, slightly hotter and more massive than the Sun. Their hydrogen lines are weaker than in A stars and metal lines become prominent. Its luminosity class III marks it as a giant: an evolved star that has left the main sequence and swollen to many times its original size.

How to find 21 Orionis in the sky

21 Orionis lies in Orion. With a declination of +2° 35.7', it is visible from the entire Northern Hemisphere and from the Southern Hemisphere down to about latitude 87° S. It is bright enough to see with the naked eye under dark skies. It is highest in the sky at local midnight around January, which makes the weeks around that month the best time to observe it.

Tabulated data for 21 Orionis

Astrometry and spectroscopy

Right Ascension (J2000)	79.79675040° (5h 19.2m)
Declination (J2000)	2.59579997° (+2° 35.7')
Galactic Longitude	199.54476702°
Galactic Latitude	-19.12520712°
Proper motion RA	-17.16 mas/yr
Proper motion Dec	-45.51 mas/yr
Parallax	16.33 ± 0.08 mas
Spectral Type	F5III-IV
Radial Velocity	8.30 km/s

Photometry

Band	Magnitude	Abs. Mag.
B	5.74	1.81
V	5.33	1.39
J	4.61	0.67
H	4.59	0.66
K	4.33	0.40

Colour index B-V: +0.42

Derivations

Heliocentric distance: 61.24 pc (200 light years) (0.5% margin of error)
Absolute visual magnitude: 1.39
Transverse velocity: 14.1 km/s
Space velocity relative to the Sun: 16.4 km/s
Galactic position (X, Y, Z): -54.5 pc, -19.4 pc, -20.1 pc
Galactic velocity (U, V, W): -1.0 km/s, -9.9 km/s, -13.0 km/s

Data: Extended Hipparcos Compilation (XHIP) and SIMBAD.