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Thuban

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description Thuban Overview

Thuban, designated Alpha Draconis, is a star in the constellation Draco that served as Earth's north pole star during much of the third millennium BCE. The shift occurred because of axial precession, the slow 26,000-year wobble of Earth's rotational axis, which gradually changes the position of the celestial pole. Although historically designated Alpha, Thuban is not the brightest star in Draco and is fainter than Gamma Draconis. It forms part of a binary system with an orbital period of approximately 51 days.

help Thuban FAQ

When was Thuban the North Star?

Thuban lay extremely close to the north celestial pole around 2700 BCE. This was during ancient Egypt's Old Kingdom, long before Polaris occupied its present position near the pole.

Why did the North Star change from Thuban to Polaris?

Earth's rotation axis slowly traces a circle against the sky through axial precession. One full cycle takes roughly 26,000 years, causing different stars to approach the celestial poles in different eras.

Is Thuban actually the brightest star in Draco?

No, despite its Alpha Draconis designation, Thuban is fainter than Eltanin, Gamma Draconis. Thuban's historical importance comes from its former position near the celestial pole, not exceptional brightness.

Is Thuban a single star?

Thuban is an eclipsing binary system whose two stars periodically pass in front of one another from Earth's viewpoint. Modern spectroscopy and space-based observations allow astronomers to measure both stellar components.

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