18 Orionis (HIP 24555)

18 Orionis is a white main-sequence star in the constellation Orion. At 392 light years away, it shines at an apparent visual magnitude of 5.51. It is moving through the Galaxy at a speed of 10.0 km/s relative to the Sun.

Sky position: RA 5h 16.1m, Dec +11° 20.5'

Common designations: 18 Orionis, HR 1718, HD 34203, HIP 24555, Gaia DR3 3387172361094938752

18 Orionis has the spectral type A0V. A-type stars are white stars with surface temperatures of roughly 7,500 to 10,000 K. Their spectra are dominated by strong hydrogen lines, and many of them rotate rapidly. Its luminosity class V means it is a main-sequence (dwarf) star, still fusing hydrogen into helium in its core like the Sun.

How to find 18 Orionis in the sky

18 Orionis lies in Orion. With a declination of +11° 20.5', it is visible from the entire Northern Hemisphere and from the Southern Hemisphere down to about latitude 79° 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 18 Orionis

Astrometry and spectroscopy

Right Ascension (J2000)	79.01722776° (5h 16.1m)
Declination (J2000)	11.34135505° (+11° 20.5')
Galactic Longitude	191.29496106°
Galactic Latitude	-15.25141368°
Proper motion RA	-7.93 mas/yr
Proper motion Dec	-6.01 mas/yr
Parallax	8.32 ± 0.08 mas
Spectral Type	A0V
Radial Velocity	-8.20 km/s

Photometry

Band	Magnitude	Abs. Mag.
B	5.50	0.10
V	5.51	0.12
J	5.44	0.04
H	5.47	0.08
K	5.46	0.06

Colour index B-V: -0.01

Derivations

Heliocentric distance: 120.16 pc (392 light years) (1.0% margin of error)
Absolute visual magnitude: 0.12
Transverse velocity: 5.7 km/s
Space velocity relative to the Sun: 10.0 km/s
Galactic position (X, Y, Z): -113.7 pc, -22.7 pc, -31.6 pc
Galactic velocity (U, V, W): 9.3 km/s, 1.4 km/s, -3.3 km/s

Data: Extended Hipparcos Compilation (XHIP) and SIMBAD.