Universe Guide


Alpha Centauri B - HD128621 - HIP71681

Alpha Centauri B is a orange to red main sequence dwarf star that can be located in the constellation of Centaurus. It is calculated at being 6.500 Billion Years old. This information comes from ExoPlanet. Alpha Centauri B is the Bayer Classification for the star. HIP71681 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD128621. The Id of the star in the Gould Star Catalogue is 364. Stars in the southern hemisphere are more likely to have a Gould Id than the northern hemisphere. For example, there are no Gould classified stars in Ursa Major. Alpha Centauri B is a multiple star system with 2 stars orbiting in its solar system.

Location of Alpha Centauri B

The location of the star in the galaxy 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 Alpha Centauri B, the location is 14h 39m 39.39 and -60d50`22.1 .

Proper Motion of Alpha Centauri B

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 802.98 ± 014.24 towards the north and -3,614.39 ± 025.90 east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Age, Radius) of Alpha Centauri B

Alpha Centauri B has a spectral type of K1V. This means the star is a orange to red main sequence dwarf star. The star has a B-V Colour Index of 0.9 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,052 Kelvin.

Alpha Centauri B has been calculated as 0.88 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 614,334.90.km.

The star is believed to be about 6.50 Billion years old. To put in context, the Sun is believed to be about five billion years old and the Universe is about 13.8 billion years old.

The star has companion stars which are in orbit close by, it has at least the following companions in close orbit, Rigil Kentaurus, Proxima Centauri.

Alpha Centauri B Apparent and Absolute Magnitudes

Alpha Centauri B has an apparent magnitude of 1.35 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 5.70 If you used the 2007 Parallax value, you would get an absolute magnitude of 5.87. 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 Alpha Centauri B

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 Alpha Centauri B 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 796.92 which put Alpha Centauri B at a distance of 4.09 light years or 1.25 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.

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

Alpha Centauri B Facts

Alternative Names

Bayer DesignationAlpha Centauri B
Hipparcos Library I.D.71681
Gould I.D.364
Henry Draper Designation128621

Visual Facts

Star Typemain sequence dwarf star
Age6.500 Billions of Years
Absolute Magnitude5.70 / 5.87
Apparent Magnitude1.35
Right Ascension (R.A.)14h 39m 39.39
Declination (Dec.)-60d50`22.1
1997 Distance from Earth742.12 Parallax (milliarcseconds)
 4.40 Light Years
 1.35 Parsecs
2007 Revised Distance from Earth796.92 Parallax (milliarcseconds)
 4.09 Light Years
 1.25 Parsecs
Proper Motion Dec.802.98 ± 14.24 milliarcseconds/year
Proper Motion RA.-3614.39 ± 25.90 milliarcseconds/year
B-V Index0.90
Spectral TypeK1V
Colour(K) Orange to Red

Companions (Multi-Star and Exoplanets) Facts

Stars in Solar System2
Companion StarsRigil Kentaurus
Proxima Centauri

Estimated Facts

Radius (x the Sun)0.88
Calculated Effective Temperature5,052 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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