Pole star

A pole star is a special star that stays almost still in the sky. This happens because it is very close to the axis of rotation of a planet or other object in space. From that planet, the pole star looks like it does not move, while other stars move around it.

For Earth, a pole star is very helpful. It helps people find direction.

Right now, Earth has two pole stars. In the north, the bright star Polaris, also called Alpha Ursae Minoris, is our main pole star. It is easy to see and has been important for finding direction for many years. In the south, there is another star called Polaris Australis, or Sigma Octantis. This star is much dimmer and harder to see.

Long ago, between about 1700 BC and 300 AD, Earth’s northern pole star was not Polaris. It was two stars called Kochab and Pherkad. These stars were twin "pole stars," but they were not as close to the exact north point in the sky as Polaris is today.

History

In classical antiquity, Beta Ursae Minoris was closer to the north pole than Alpha Ursae Minoris (Polaris). The Phoenicians used the whole Ursa Minor to find north. Polaris was later called aeiphanes, meaning "always above the horizon." In Anglo-Saxon England, it was known as scip-steorra, or "ship-star," because it helped with navigation. The name stella polaris was created during the Renaissance, even though Polaris was not exactly at the north pole.

Precession of the equinoxes

The North Star is a special star that looks like it sits right above Earth's North Pole. Over time, this star changes because Earth moves in a way called the precession of the equinoxes. Earth wobbles slowly, like a spinning top, and it takes about 26,000 years to finish one full wobble. Because of this movement, different stars become the North Star at different times.

Right now, Polaris is our North Star. It is very close to the north celestial pole. In the past, other stars like Thuban in the constellation Draco were the North Star. In the future, stars in constellations such as Cepheus, Cygnus, Lyra, and Hercules will be the North Star. Sometimes, no single star will be close enough to be a clear North Star. At other times, stars will only give an approximate idea of which way is north.

Southern pole star (South Star)

Currently, Earth does not have a bright star like Polaris to guide us from the South Pole. The closest star is Sigma Octantis, but it is quite dim and hard to see. This star is a yellow giant located 294 light years from Earth.

The Southern Cross constellation helps point toward where a southern pole star would be. Over thousands of years, different stars will move closer to the south celestial pole. In the far future, Sirius might become a southern guide star.

Other planets

Pole stars of other planets are stars that look closest to the point where the planet's axis of rotation touches the sky. These stars need to be bright enough to see without a telescope, usually brighter than magnitude 6. Because each planet spins at a different angle, they each have their own special pole stars. For more information, see Poles of astronomical bodies.

In religion and mythology

Polaris, the North Pole Star, has been important in many cultures and religions. In medieval times, it was called stella maris, meaning "star of the sea," because it helped guide sailors. It was also linked to Marian veneration, with Our Lady, Star of the Sea being a title for the Virgin Mary.

In Mandaean cosmology, the Pole Star is seen as a sign of the World of Light, and people face north when they pray. In Hinduism, the Pole Star is known as Dhruva, named after a devoted follower of the god Vishnu who became the Pole Star.