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Omicron2 Centauri, HD100262, HIP56250, HR4442

Omicron2 Centauri is a blue pulsating supergiant star that can be located in the constellation of Centaurus. 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.

Omicron2 Centauri's Alternative Names

Omicron2 Centauri (Omi02 Cen) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR4442. HIP56250 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD100262.

Omicron2 Centauri has alternative name(s) :- , omi02 Cen.

The Gould star designation is one that was designed by American astronomer, Benjamin Apthorp Gould. Gould stars are predominantly in the Southern and Equatorial constellations but do appear in northern constellations such as Bootes and Orion. The star has the designation 38 G. Centauri. There are no stars with a Gould designation in Ursa Major for example.

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

Location of Omicron2 Centauri

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 Omicron2 Centauri, the location is 11h 31m 48.81 and -59° 30` 56.3 .

Proper Motion of Omicron2 Centauri

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 1.12 ± 0.20 miliarcseconds/year towards the north and -6.89 ± 0.28 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 -16.80000 km/s with an error of about 2.80 km/s .

Physical Properties (Colour, Temperature) of Omicron2 Centauri

Omicron2 Centauri has a spectral type of A3Ia. This means the star is a blue supergiant star. The star has a B-V Colour Index of 0.43 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,305 Kelvin.

Omicron2 Centauri Radius has been calculated as being 77.19 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 53,711,396.17.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 121.22. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Omicron2 Centauri Apparent and Absolute Magnitudes

Omicron2 Centauri has an apparent magnitude of 5.12 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 -4.97 If you used the 2007 Parallax value, you would get an absolute magnitude of -5.95. 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 Omicron2 Centauri

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 0.96 which gave the calculated distance to Omicron2 Centauri as 3397.53 light years away from Earth or 1041.67 parsecs. It would take a spaceship travelling at the speed of light, 3397.53 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 0.61 which put Omicron2 Centauri at a distance of 5346.94 light years or 1639.34 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.

Variable Type of Omicron2 Centauri

The star is a pulsating Alpha Cygnus variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. Omicron2 Centauri brightness ranges from a magnitude of 5.281 to a magnitude of 5.233 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.0 days (variability).

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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Omicron2 Centauri Facts

Visual Facts


Primary / Proper / Traditional NameOmicron2 Centauri
Alternative NamesOmi02 Cen, HD 100262, HIP 56250, HR 4442, 38 G. Centauri, omi02 Cen
Spectral TypeA3Ia
Multiple Star SystemYes
Star Type very luminous Supergiant Star
Colour blue
GalaxyMilky Way
ConstellationCentaurus
Absolute Magnitude-4.97 / -5.95
Visual / Apparent Magnitude5.12
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)11h 31m 48.81
Declination (Dec.)-59° 30` 56.3
Galactic Latitude1.81 degrees
Galactic Longitude292.98 degrees
1997 Distance from Earth0.96 Parallax (milliarcseconds)
 3397.53 Light Years
 1041.67 Parsecs
2007 Distance from Earth0.61 Parallax (milliarcseconds)
 5346.94 Light Years
 1639.34 Parsecs
Proper Motion Dec.1.12 ± 0.20 milliarcseconds/year
Proper Motion RA.-6.89 ± 0.28 milliarcseconds/year
B-V Index0.43
Radial Velocity-16.80 ± 2.80 km/s
Associated / Clustered StarsOmicron Centauri

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeAlpha Cygnus
Mean Variability Period in Days0.044
Variable Magnitude Range (Brighter - Dimmer)5.233 - 5.281

Estimated Facts


Calculated Effective Temperature6,305 Kelvin

Sources and Links


SIMBAD SourceLink

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