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Thuban (Alpha Draconis)





Thuban. Credit: ESO
The fourth brightest star in the constellation Draco. Thuban used to be the pole star, a distinction it held from 3942 BC to 1793 BC when it was superceded by the faint star Kappa Draconis. In 2787 BC, it lay just 1/180 the width of the full Moon from the pole. Thuban was considered the pole star until about 1900 BC, when the much brighter Kochab began to approach the pole as well.

Although Thuban lies in the Dragon's tail, its name comes from an Arabic phrase that means "the Serpent's head." Thuban belongs to the fairly rare class of giant A stars. It has a faint unseen companion in a 51.4-day orbit that may be a red dwarf or a low-mass white dwarf.


visual magnitude 3.67
absolute magnitude -1.21
spectral type A0III
surface temperature 9,500 K
luminosity 265 Lsun
distance 309 light-years (94 pc)
position R.A. 14h 04m 23.3s,
Dec. +64 22' 33.1"
other designations 11 Draconis, BD+65 978, HD 123299,
HIP 68756, HR 5291, SAO 16273


Related category

   • NOTABLE STARS