21 Eridani (HIP 17027)

21 Eridani is an orange subgiant star in the constellation Eridanus. At 113 light years away, it shines at an apparent visual magnitude of 5.96. It is moving through the Galaxy at a speed of 53.0 km/s relative to the Sun.

Sky position: RA 3h 39.0m, Dec -5° 37.6'

Common designations: 21 Eridani, HR 1111, HD 22713, HIP 17027, Gaia DR3 3247680138377334912

21 Eridani has the spectral type K0IV. K-type stars are orange stars with surface temperatures of about 3,900 to 5,300 K. Their spectra are rich in neutral metal lines and, in the cooler examples, molecular bands. Its luminosity class IV marks it as a subgiant: it has exhausted hydrogen in its core and is beginning to expand toward the giant phase.

How to find 21 Eridani in the sky

21 Eridani lies in Eridanus. With a declination of -5° 37.6', it is visible from the entire Southern Hemisphere and from the Northern Hemisphere up to about latitude 84° N. It is bright enough to see with the naked eye under dark skies. It is highest in the sky at local midnight around December, which makes the weeks around that month the best time to observe it.

Tabulated data for 21 Eridani

Astrometry and spectroscopy

Right Ascension (J2000)	54.75465215° (3h 39.0m)
Declination (J2000)	-5.62621344° (-5° 37.6')
Galactic Longitude	192.27584136°
Galactic Latitude	-44.74807819°
Proper motion RA	-15.66 mas/yr
Proper motion Dec	-208.73 mas/yr
Parallax	28.89 ± 0.03 mas
Spectral Type	K0IV
Radial Velocity	40.30 km/s

Photometry

Band	Magnitude	Abs. Mag.
B	6.88	4.18
V	5.96	3.26
J	4.74	2.04
H	4.09	1.39
K	4.03	1.33

Colour index B-V: +0.92

Derivations

Heliocentric distance: 34.62 pc (113 light years) (0.1% margin of error)
Absolute visual magnitude: 3.26
Transverse velocity: 34.3 km/s
Space velocity relative to the Sun: 53.0 km/s
Galactic position (X, Y, Z): -24.0 pc, -5.2 pc, -24.4 pc
Galactic velocity (U, V, W): -7.8 km/s, -29.6 km/s, -43.2 km/s

Data: Extended Hipparcos Compilation (XHIP) and SIMBAD.