21 Orionis is a blue to white luminous giant star that can be located in the constellation of Orion. HIP24817 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD34658. 21 Orionis has alternative name(s), 21 Orionis , 21 Ori.
The location of the star in the galaxy is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For 21 Orionis, the location is 05h 19m 11.23 and +02d35`45.4 .
All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -053.15 ± 000.19 towards the north and -017.74 ± 000.39 east if we saw them in the horizon.
21 Orionis has a spectral type of F5IIvar. This means the star is a blue to white luminous giant star. The star has a B-V Colour Index of 0.41 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,366 Kelvin.
21 Orionis has been calculated as 3.99 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,777,414.00.km.
21 Orionis has an apparent magnitude of 5.34 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of 1.42 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.38. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.
Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 16.47 which gave the calculated distance to 21 Orionis as 198.03 light years away from Earth or 60.72 parsecs. It would take a spaceship travelling at the speed of light, 198.03 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.
In 2007, Hipparcos data was revised with a new parallax of 16.14 which put 21 Orionis at a distance of 202.08 light years or 61.96 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.
The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.
|Traditional Name||21 Orionis|
|Short Name||21 Ori|
|Alternative Name(s)||21 Orionis|
|Hipparcos Library I.D.||24817|
|Bonner Durchmusterung||BD+02 916|
|Henry Draper Designation||34658|
|Star Type||luminous giant star|
|Absolute Magnitude||1.42 / 1.38|
|Right Ascension (R.A.)||05h 19m 11.23|
|1997 Distance from Earth||16.47 Parallax (milliarcseconds)|
|198.03 Light Years|
|2007 Revised Distance from Earth||16.14 Parallax (milliarcseconds)|
|202.08 Light Years|
|Proper Motion Dec.||-53.15 ± 0.19 milliarcseconds/year|
|Proper Motion RA.||-17.74 ± 0.39 milliarcseconds/year|
|Colour||(F) blue to white|
|Radius (x the Sun)||3.99|
|Calculated Effective Temperature||6,366 Kelvin|