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Eta Centauri, HD127972, HIP71352, HR5440

Eta Centauri is a blue eclipsing binary system main sequence dwarf 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.

Eta Centauri's Alternative Names

Eta Centauri (Eta Cen) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR5440. HIP71352 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD127972.

Eta Centauri has alternative name(s) :- Eta CenTau, eta 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 356 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 Eta 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 Eta Centauri, the location is 14h 35m 30.45 and -42° 09` 27.9 .

Proper Motion of Eta 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 -32.72 ± 0.11 miliarcseconds/year towards the north and -34.73 ± 0.21 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 0.00000 km/s with an error of about 1.60 km/s .

Eta Centauri 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 2,432.97 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 Eta Centauri

Eta Centauri has a spectral type of B1Vn + A. This means the star is a blue main sequence dwarf star. The star is 7,329.00 Parsecs from the Galactic Centre or terms of Light Years is 23,904.51 s. The star has a B-V Colour Index of -0.15 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 13,674 Kelvin.

Eta Centauri Radius has been calculated as being 5.38 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,746,465.29.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 5.34. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Eta Centauri Apparent and Absolute Magnitudes

Eta Centauri has an apparent magnitude of 2.33 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 -2.55 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.53. 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 Eta Centauri

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 10.57 which gave the calculated distance to Eta Centauri as 308.57 light years away from Earth or 94.61 parsecs. It would take a spaceship travelling at the speed of light, 308.57 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 10.67 which put Eta Centauri at a distance of 305.68 light years or 93.72 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 7,329.00 Parsecs or 23,904.51 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Eta Centauri

The star is a eclipsing binary system Beta Lyrae (Sheliak) 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. Eta Centauri brightness ranges from a magnitude of 2.338 to a magnitude of 2.255 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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Eta Centauri Facts

Visual Facts


Primary / Proper / Traditional NameEta Centauri
Alternative NamesEta Cen, Eta CenTau, HD 127972, HIP 71352, HR 5440, 356 G. Centauri, eta Cen
Spectral TypeB1Vn + A
Multiple Star SystemNo / Unknown
Star Type main sequence Dwarf Star
Colour blue
GalaxyMilky Way
ConstellationCentaurus
Absolute Magnitude-2.55 / -2.53
Visual / Apparent Magnitude2.33
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)14h 35m 30.45
Declination (Dec.)-42° 09` 27.9
Galactic Latitude16.67 degrees
Galactic Longitude322.77 degrees
1997 Distance from Earth10.57 Parallax (milliarcseconds)
 308.57 Light Years
 94.61 Parsecs
2007 Distance from Earth10.67 Parallax (milliarcseconds)
 305.68 Light Years
 93.72 Parsecs
Galacto-Centric Distance23,904.51 Light Years / 7,329.00 Parsecs
Proper Motion Dec.-32.72 ± 0.11 milliarcseconds/year
Proper Motion RA.-34.73 ± 0.21 milliarcseconds/year
B-V Index-0.15
Radial Velocity0.00 ± 1.60 km/s
Eccentricity0.04
Semi-Major Axis7088.00
Stellar Luminosity (Lsun)2,432.97

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEclipsing binary system
Variable Star TypeBeta Lyrae (Sheliak)
Mean Variability Period in Days1.285
Variable Magnitude Range (Brighter - Dimmer)2.255 - 2.338

Estimated Facts


Calculated Effective Temperature13,674 Kelvin

Sources and Links


SIMBAD SourceLink

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