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55 Orionis, HD39291, HIP27658, HR2031

55 Orionis is a blue subgiant star that can be located in the constellation of Orion. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

55 Orionis's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR2031. HIP27658 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD39291.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 55 Orionis with it shortened to 55 Ori.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD-07 1187.

More details on star alternative names can be found at Star Names .

Location of 55 Orionis

The location of the star in the night sky 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 55 Orionis, the location is 05h 51m 21.98 and -07° 31` 04.8 .

Proper Motion of 55 Orionis

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 -0.51 ± 0.17 miliarcseconds/year towards the north and 0.31 ± 0.27 miliarcseconds/year east if we saw them in the horizon. The Radial Velocity, that is the speed at which the star is moving away/towards us is 12.60000 km/s with an error of about 1.50 km/s .

55 Orionis Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 2,538.98 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of 55 Orionis

55 Orionis has a spectral type of B2IV-V. This means the star is a blue subgiant star. The star is 7,658.00 Parsecs from the Galactic Centre or terms of Light Years is 24,977.59 s. The star has a B-V Colour Index of -0.19 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 16,152 Kelvin.

55 Orionis Radius has been calculated as being 5.21 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,622,151.69.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 3.25. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

55 Orionis Apparent and Absolute Magnitudes

55 Orionis has an apparent magnitude of 5.36 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 -3.20 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.18. 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.

Distance to 55 Orionis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 1.94 which gave the calculated distance to 55 Orionis as 1681.25 light years away from Earth or 515.46 parsecs. It would take a spaceship travelling at the speed of light, 1681.25 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 3.11 which put 55 Orionis at a distance of 1048.76 light years or 321.54 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 star's Galacto-Centric Distance is 7,658.00 Parsecs or 24,977.59 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Source of Information

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 Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

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55 Orionis Facts

Visual Facts


Primary / Proper / Traditional Name55 Orionis
Alternative NamesHD 39291, HIP 27658, HR 2031, 55 Ori, BD-07 1187
Spectral TypeB2IV-V
Multiple Star SystemNo / Unknown
Star TypeSubgiant Star
Colour blue
GalaxyMilky Way
ConstellationOrion
Absolute Magnitude-3.20 / -2.18
Visual / Apparent Magnitude5.36
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)05h 51m 21.98
Declination (Dec.)-07° 31` 04.8
Galactic Latitude-16.76 degrees
Galactic Longitude212.89 degrees
1997 Distance from Earth1.94 Parallax (milliarcseconds)
 1681.25 Light Years
 515.46 Parsecs
2007 Distance from Earth3.11 Parallax (milliarcseconds)
 1048.76 Light Years
 321.54 Parsecs
Galacto-Centric Distance24,977.59 Light Years / 7,658.00 Parsecs
Proper Motion Dec.-0.51 ± 0.17 milliarcseconds/year
Proper Motion RA.0.31 ± 0.27 milliarcseconds/year
B-V Index-0.19
Radial Velocity12.60 ± 1.50 km/s
Eccentricity0.12
Semi-Major Axis8534.00
Stellar Luminosity (Lsun)2,538.98

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Facts


Calculated Effective Temperature16,152 Kelvin

Sources and Links


SIMBAD SourceLink

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