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Rigil Kentaurus, Alpha Centauri, HD128620, HIP71683, HR5459

Rigil Kentaurus (Alpha Centauri) Location in Centaurus

Rigil Kentaurus (Alpha Centauri) is a white to yellow main sequence dwarf star that can be located in the constellation of Centaurus. The description is based on the spectral class. Rigil Kentaurus is a main star of the constellation.

Rigil Kentaurus is the 3rd brightest star in the night sky and is the brightest star in Centaurus based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it. The star has an estimated age of 9.20 Billion of Years but could be as young as 8.10 to 10.20 according to Hipparcos.

Rigil Kentaurus is more famously known as simply Alpha Centauri which is one of the closest stars to our own solar system. The star is a Mutiple Star System where one star orbits the other and both being roughly the same size.

Being the closest star, it features in many science fiction stories and films such as in Avatar where the moon of Pandora is orbiting one of the star`s planets. There has been speculation that there is in fact a few Extrasolar Planets (Exoplanets) in orbit round the planet which if true would make it the closest exoplanet to ours. Before getting too excited, you need to realise it is still far far away to get to. If you could fit the entire Solar System into your room, you would probably be talking situating Rigil some four miles (roughly) away. We just don`t have the technology to get there. Alpha Centauri is roughly about the same size as the The Sun and so will die roughly or before the Sun.

Rigil Kentaurus's Alternative Names

Alpha Centauri (Alf Cen) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR5459. HIP71683 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD128620. The Gliese ID of the star is GL 559A. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

Rigil Kentaurus has alternative name(s) :- Alpha CenTau.

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 363 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 Rigil Kentaurus

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 Rigil Kentaurus, the location is 14h 39m 40.90 and -60° 50` 06.5 .

Radial Velocity and Proper Motion of Rigil Kentaurus

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 473.67 ± 2.46 miliarcseconds/year towards the north and -3,679.25 ± 4.11 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 -21.40 km/s with an error of about 0.76 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.

Rigil Kentaurus 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 1.77 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, Age) of Rigil Kentaurus

Rigil Kentaurus has a spectral type of G2V. This means the star is a white to yellow main sequence dwarf star. The star is 7,399.00 Parsecs from the Galactic Centre or terms of Light Years is 24,132.83 s. The star has a B-V Colour Index of 0.71 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,533 Kelvin.

Rigil Kentaurus Radius has been calculated as being 1.38 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 958,128.77.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 1.35. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.20 with an error value of 0.01 Fe/H with the Sun has a value of 1 to put it into context.

The stars age according to Hipparcos data files put the star at an age of about 9.20 Billion years old but could be between 8.10 and 10.20 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

Rigil Kentaurus Apparent and Absolute Magnitudes

Rigil Kentaurus has an apparent magnitude of -0.01 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 4.34 If you used the 2007 Parallax value, you would get an absolute magnitude of 4.39. 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 Rigil Kentaurus

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 742.12 which gave the calculated distance to Rigil Kentaurus as 4.40 light years away from Earth or 1.35 parsecs. It would take a spaceship travelling at the speed of light, 4.40 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 754.81 which put Rigil Kentaurus at a distance of 4.32 light years or 1.32 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 272,267.65 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.

The star's Galacto-Centric Distance is 7,399.00 Parsecs or 24,132.83 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Meteor Showers Radiating from near Rigil Kentaurus

The Alpha Centaurids Meteor Shower radiants from a point near this star. The meteor shower runs typically between Jan 28 - Feb 21 with a peak date of Feb 07. The speed of a meteor in the shower is 58 Km/s. The amount of meteors predicted to be seen per hour (Zenith Hourly Rate) is 58.

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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Rigil Kentaurus Facts

Visual Facts


Primary / Proper / Traditional NameRigil Kentaurus
Alternative NamesAlpha Centauri, Alf Cen, Alpha CenTau, HD 128620, HIP 71683, HR 5459, 363 G. Centauri, Gliese 559A
Spectral TypeG2V
Constellation's Main StarYes
Multiple Star SystemYes
Star Type main sequence Dwarf Star
Colour white to yellow
GalaxyMilky Way
ConstellationCentaurus
Age9.20 Billion Years Old
Age Range8.10 - 10.20 Billion Years Old
Absolute Magnitude 4.34 / 4.39
Visual / Apparent Magnitude-0.01
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)14h 39m 40.90
Declination (Dec.)-60° 50` 06.5
Galactic Latitude-0.68 degrees
Galactic Longitude315.74 degrees
1997 Distance from Earth742.12 Parallax (milliarcseconds)
 4.40 Light Years
 1.35 Parsecs
2007 Distance from Earth754.81 Parallax (milliarcseconds)
 4.32 Light Years
 1.32 Parsecs
 272,267.65 Astronomical Units
Galacto-Centric Distance24,132.83 Light Years / 7,399.00 Parsecs
Proper Motion Dec.473.67 ± 2.46 milliarcseconds/year
Proper Motion RA.-3679.25 ± 4.11 milliarcseconds/year
B-V Index0.71
Radial Velocity-21.40 ± 0.76 km/s
Iron Abundance0.20 ± 0.01 Fe/H
Eccentricity0.17
Semi-Major Axis8681.00
Stellar Luminosity (Lsun)1.77
Brightest in Night Sky3rd
Associated / Clustered StarsAlpha Centauri B
Proxima Centauri

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Facts


Calculated Effective Temperature5,533 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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