51 Eridani (HIP 21547)

51 Eridani is a yellow-white subgiant star in the constellation Eridanus. At 98 light years away, it shines at an apparent visual magnitude of 5.21. It is moving through the Galaxy at a speed of 16.7 km/s relative to the Sun.

Sky position: RA 4h 37.6m, Dec -2° 28.4'

Common designations: 51 Eridani, c Eridani, HR 1474, HD 29391, HIP 21547, Gaia DR3 3205095125321700480

51 Eridani has the spectral type F0IV. 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 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 51 Eridani in the sky

51 Eridani lies in Eridanus. With a declination of -2° 28.4', it is visible from the entire Southern Hemisphere and from the Northern Hemisphere up to about latitude 88° 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 51 Eridani

Astrometry and spectroscopy

Right Ascension (J2000)	69.40055254° (4h 37.6m)
Declination (J2000)	-2.47354881° (-2° 28.4')
Galactic Longitude	198.61258248°
Galactic Latitude	-30.65766167°
Proper motion RA	44.05 mas/yr
Proper motion Dec	-64.03 mas/yr
Parallax	33.44 ± 0.08 mas
Spectral Type	F0IV
Radial Velocity	12.60 km/s

Photometry

Band	Magnitude	Abs. Mag.
B	5.49	3.11
V	5.21	2.83
J	4.74	2.37
H	4.77	2.39
K	4.54	2.16

Colour index B-V: +0.28

Derivations

Heliocentric distance: 29.91 pc (98 light years) (0.2% margin of error)
Absolute visual magnitude: 2.83
Transverse velocity: 11.0 km/s
Space velocity relative to the Sun: 16.7 km/s
Galactic position (X, Y, Z): -24.4 pc, -8.2 pc, -15.2 pc
Galactic velocity (U, V, W): -7.2 km/s, -14.0 km/s, -5.7 km/s

Data: Extended Hipparcos Compilation (XHIP) and SIMBAD.