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CO Orionis, HIP25540

CO Orionis is a white to yellow main sequence dwarf star that can be located in the constellation of Orion. The description is based on the spectral class. CO Orionis is not part of the constellation but is within the borders of the constellation.

The star can not be seen by the naked eye, you need a telescope to see it.

CO Orionis's Alternative Names

HIP25540 is the reference name for the star in the Hipparcos Star Catalogue.

CO Orionis has alternative name(s) :- , CO 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+11 809.

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

Location of CO 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 CO Orionis, the location is 05h 27m 38.33 and +11° 25` 38.9 .

Radial Velocity and Proper Motion of CO 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 3.49 ± 1.73 miliarcseconds/year towards the north and 7.65 ± 3.02 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 the Sun is 23.00 km/s with an error of about 5.50 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties (Colour, Temperature) of CO Orionis

CO Orionis has a spectral type of G5Vpe. This means the star is a white to yellow main sequence dwarf star. The star has a B-V Colour Index of 0.98 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,888 Kelvin.

CO Orionis Apparent and Absolute Magnitudes

CO Orionis has an apparent magnitude of 10.64 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 If you used the 2007 Parallax value, you would get an absolute magnitude of 3.08. 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 CO Orionis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as -1.82 which gave the calculated distance to CO Orionis as -1792.11 light years away from Earth or -549.45 parsecs. It would take a spaceship travelling at the speed of light, -1792.11 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 3.07 which put CO Orionis at a distance of 1062.42 light years or 325.73 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.

Using the 2007 distance, the star is roughly 67,186,167.18 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun. CO Orionis brightness ranges from a magnitude of 11.753 to a magnitude of 10.465 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 1.3 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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CO Orionis Facts

Visual Facts


Primary / Proper / Traditional NameCO Orionis
Alternative NamesHIP 25540, BD+11 809, CO Ori
Spectral TypeG5Vpe
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star Type main sequence Dwarf Star
Colour white to yellow
GalaxyMilky Way
ConstellationOrion
Absolute Magnitude / 3.08
Visual / Apparent Magnitude10.64
Naked Eye VisibleRequires a 4.5 - 6 Inch Telescope - Magnitudes
Right Ascension (R.A.)05h 27m 38.33
Declination (Dec.)+11° 25` 38.9
Galactic Latitude-12.80 degrees
Galactic Longitude192.77 degrees
1997 Distance from Earth-1.82 Parallax (milliarcseconds)
 -1792.11 Light Years
 -549.45 Parsecs
2007 Distance from Earth3.07 Parallax (milliarcseconds)
 1062.42 Light Years
 325.73 Parsecs
 67,186,167.18 Astronomical Units
Proper Motion Dec.3.49 ± 1.73 milliarcseconds/year
Proper Motion RA.7.65 ± 3.02 milliarcseconds/year
B-V Index0.98
Radial Velocity23.00 ± 5.50 km/s

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Mean Variability Period in Days1.268
Variable Magnitude Range (Brighter - Dimmer)10.465 - 11.753

Estimated Facts


Calculated Effective Temperature4,888 Kelvin

Sources and Links


SIMBAD SourceLink

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