45 Eridani (HIP 21139)

45 Eridani is an orange giant star in the constellation Eridanus. At 871 light years away, it shines at an apparent visual magnitude of 4.90. It is moving through the Galaxy at a speed of 18.2 km/s relative to the Sun.

Sky position: RA 4h 31.9m, Dec -0° 2.6'

Common designations: 45 Eridani, HR 1437, HD 28749, HIP 21139, Gaia DR3 3230572046686872192

45 Eridani has the spectral type K0/1III. 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 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 45 Eridani in the sky

45 Eridani lies in Eridanus. With a declination of -0° 2.6', it is visible from the entire Southern Hemisphere and from the Northern Hemisphere up to about latitude 90° 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 45 Eridani

Astrometry and spectroscopy

Right Ascension (J2000)	67.96945262° (4h 31.9m)
Declination (J2000)	-0.04401107° (-0° 2.6')
Galactic Longitude	195.33564309°
Galactic Latitude	-30.62560526°
Proper motion RA	-1.47 mas/yr
Proper motion Dec	-7.68 mas/yr
Parallax	3.74 ± 0.10 mas
Spectral Type	K0/1III
Radial Velocity	15.22 km/s

Photometry

Band	Magnitude	Abs. Mag.
B	6.22	-0.92
V	4.90	-2.24
J	2.88	-4.26
H	2.24	-4.89
K	2.08	-5.05

Colour index B-V: +1.32

Derivations

Heliocentric distance: 267.18 pc (871 light years) (2.7% margin of error)
Absolute visual magnitude: -2.24
Transverse velocity: 9.9 km/s
Space velocity relative to the Sun: 18.2 km/s
Galactic position (X, Y, Z): -221.7 pc, -60.8 pc, -136.1 pc
Galactic velocity (U, V, W): -7.4 km/s, -9.6 km/s, -13.5 km/s

Data: Extended Hipparcos Compilation (XHIP) and SIMBAD.