Universe Guide

Thuban (Alpha Draconis, 11 Draconis) Star Facts

Thuban Facts

  • Thuban is a giant star that can be located in the constellation of Draco. The description is based on the spectral class.
  • Thuban is a main star of the constellation outline.
  • Based on the spectral type (A0III SB) of the star, the star's colour is blue - white .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • Thuban has a radius that is 3.40 times bigger than the Suns. Radius
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 303.13 light years away from us. Distance

Information on Thuban

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.

Thuban's Alternative Names

Alpha Draconis (Alf Dra) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

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.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 11 Draconis. The Flamsteed name can be shortened to 11 Dra.

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+65 978.

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

Location of Thuban

The location of the giant 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 object is compared to the celestial equator and is expressed in degrees. For Thuban, the location is 14h 04m 23.43 and +64° 22` 32.9 .

Radial Velocity and Proper Motion of Thuban

Proper Motion

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

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -14.00000 km/s with an error of about 1.78 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 of Thuban

Thuban Temperature and Colour

Based on the star's spectral type of A0III SB , Thuban's colour and type is blue - white giant star. The star's effective temperature is 10,100 Kelvin which is hotter than our own Sun's effective Temperature which is 5,777 Kelvin.

Thuban 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 341.76 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Thuban Radius

Thuban Radius has been calculated as being 3.40 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,365,720.00.km. If you need the diameter of the star, you just need to multiple the radius by 2.

Thuban Mass

The Thuban's solar mass is 2.80 times that of our star, the Sun. The Sun's Mass is 1,989,100,000,000,000,000,000 billion kg. which to calculate using this website is too large. To give idea of size, the Sun is 99.86% the mass of the solar system.

Thuban Iron Abundance

Thuban 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. The value comes from the Hipparcos Extended Catalog.

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 10.56000 which gave the calculated distance to Thuban as 308.87 light years away from Earth or 94.70 parsecs. If you want that in miles, it is about 1,815,731,019,015,221.62, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 10.76000 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.

Using the 2007 distance, the star is roughly 19,170,117.51 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 7,421.00 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*.

Travel Time to Thuban

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Airbus A380736276,201,112.43
Speed of Sound (Mach 1)767.269264,944,913.39
Concorde (Mach 2)1,534.54132,472,284.04
New Horizons Probe33,0006,160,121.78
Speed of Light670,616,629.00303.13

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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Additional Thuban Facts and Figures

Visual Facts

Primary / Proper / Traditional NameThuban
Alternative NamesAlpha Draconis, Alf Dra, HD 123299, HIP 68756, HR 5291, 11 Draconis, 11 Dra, BD+65 978
Spectral TypeA0III SB
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeGiant Star
GalaxyMilky Way
Absolute Magnitude -1.21 / -1.17
Visual / Apparent Magnitude3.67
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)14h 04m 23.43
Declination (Dec.)+64° 22` 32.9
Galactic Latitude50.95872942 degrees
Galactic Longitude110.52351394 degrees
1997 Distance from Earth10.56000 Parallax (milliarcseconds)
 308.87 Light Years
 94.70 Parsecs
2007 Distance from Earth10.76000 Parallax (milliarcseconds)
 303.13 Light Years
 92.94 Parsecs
 19,170,117.51 Astronomical Units
Galacto-Centric Distance24,204.58 Light Years / 7,421.00 Parsecs
Proper Motion Dec.17.21000 ± 0.15000 milliarcseconds/year
Proper Motion RA.-56.34000 ± 0.17000 milliarcseconds/year
B-V Index-0.04
Radial Velocity-14.00000 ± 1.78 km/s
Iron Abundance-0.1400 ± 0.04 Fe/H
Semi-Major Axis7056.0000000
Stellar Luminosity (Lsun)341.7600000
Orbital Period (Days)51.41670
Argument Of Periastron23.20000

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Estimated Calculated Facts

Radius (x the Sun)3.40
Effective Temperature10,195 Kelvin
Mass Compared to the Sun2.80

Sources and Links

SIMBAD SourceLink

Location of Thuban in Draco

Thuban Location in Draco

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

Draco Main Stars

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