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Thuban (Alpha Draconis) - HD123299 - HIP68756 - HR5291

Thuban (Alpha Draconis) is a blue giant star that can be located in the constellation of Draco. Thuban is the brightest star in Draco 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.

Alpha Draconis is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR5291. HIP68756 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD123299.

Thuban has alternative name(s), 11 Draconis , 11 Dra.

Thuban, the Pole Star

When people talk about the Pole Star, we talk about Polaris being the nearly geostationary star above the north pole. Its not always been the case though with Polaris. In 3,000 B.C., the Pole Star was Thuban, not Polaris. The reason for the change is the rotational axis of the Earth. The Earth spins on its axis every 26,000 years so one day, Thuban might regain its title again. Ref: N.A.S.A.

Location of Thuban

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 Thuban, the location is 14h 04m 23.43 and +64d22`32.9 .

Proper Motion of Thuban

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 17.21 ± 0.15 miliarcseconds/year towards the north and -56.34 ± 0.17 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Thuban

Thuban has a spectral type of A0III SB. This means the star is a blue giant star. The star is 7421.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24204.5817582400000000s. The star has a B-V Colour Index of -0.04 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 10,195 Kelvin.

Thuban Radius has been calculated as being 5.23 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,636,011.51.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 5.13. 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 -0.14 with an error value of 0.04 Fe/H with the Sun has a value of 1 to put it into context.

Thuban Apparent and Absolute Magnitudes

Thuban has an apparent magnitude of 3.67 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 -1.21 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.17. 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 Thuban

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 10.56 which gave the calculated distance to Thuban as 308.87 light years away from Earth or 94.70 parsecs. It would take a spaceship travelling at the speed of light, 308.87 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 10.76 which put Thuban at a distance of 303.13 light years or 92.94 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 7,421.00 Parsecs or 24,204.58 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

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.

Thuban Facts

Alternative Names

Traditional/Proper NameThuban
Short Name11 Dra
Bayer DesignationAlpha Draconis
Alternative Name(s)11 Draconis
Hipparcos Library I.D.68756
Yale Bright Star Catalogue (HR) Id5291
Bonner DurchmusterungBDD+65 978
Henry Draper Designation123299

Visual Facts

Star Typegiant star
Absolute Magnitude-1.21 / -1.17
Visual / Apparent Magnitude3.67
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)14h 04m 23.43
Declination (Dec.)+64d22`32.9
Galactic Latitude50.96 degrees
Galactic Longitude110.52 degrees
1997 Distance from Earth10.56 Parallax (milliarcseconds)
 308.87 Light Years
 94.70 Parsecs
2007 Revised Distance from Earth10.76 Parallax (milliarcseconds)
 303.13 Light Years
 92.94 Parsecs
Galacto-Centric Distance24,204.58 Light Years / 7,421.00 Parsecs
Proper Motion Dec.17.21 ± 0.15 milliarcseconds/year
Proper Motion RA.-56.34 ± 0.17 milliarcseconds/year
B-V Index-0.04
Radial Velocity-14.00 ± 1.78 km/s
Iron Abundance-0.14 ± 0.04 Fe/H
Eccentricity0.40
Inclination131.78
Semi-Major Axis1.46
Orbital Period (Days)51.42
Argument Of Periastron23.20
Spectral TypeA0III SB
Colour(A) blue

Estimated Facts

Calculated Effective Temperature10,195 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Location of Thuban in Draco


Thuban (Alpha Draconis) Location in Draco

The map was generated using Night Vision, an awesome free application by Brian Simpson.


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