Learn more about the constellation of Ursa Minor and the brightest star within it, Polaris, used for centuries by sailors for navigating at sea
Polaris is the brightest star in the Ursa Minor constellation, and for centuries was used by sailors for navigating at sea.
Astronomers usually call the Little Bear constellation Ursa Minor (Latin for ‘little bear’). In North America, the shape is called the Little Dipper.
By far the most important and famous star in Ursa Minor is the North Star or Pole Star, known as Polaris. This is the star at the very end of the bear’s long tail.
The reason Polaris is so important is that it is almost directly above the North Pole. This means you can use it like a compass to find north.
What's more, the angle of the star above the horizon gives you your latitude (north-south position on the Earth’s surface). For years, sailors relied on the North Star for navigating at sea, with the help of instruments like quadrants and astrolabes.
You can find the North Star, Polaris, by following a line drawn through Dubhe and Merak, the two end stars in the bowl part of Ursa Major (Great Bear).
The ancient Greeks realised that Polaris did not mark the pole exactly. We now know that the earth’s axis moves slowly backwards and forwards over thousands of years, so the star nearest the pole changes over time.
About 5,000 years ago, a star called Thuban was the Pole Star and in about 5,000 years’ time, a star called Alderamin in the constellation Cepheus will be nearest the pole. Eventually, in about 28,000 years, Polaris will be the Pole Star once again.
Polaris is interesting to astronomers because it is a pulsating ‘supergiant’.
Supergiants are the largest and brightest stars, often many hundred times larger (and much brighter) than our Sun.
However, Polaris does not look very bright to us because it is so far away. Polaris is 431 light years away from Earth: over 6400 million million kilometres (4000 million million miles).
There are many different legends about the Pole Star in different cultures.
In Arabic mythology, it is an evil star that killed the great warrior of the sky. The dead warrior now lies in the coffin of the 'Funeral Bier' constellation – the Arabic name for the Great Bear.
In Norse mythology the Pole Star is the jewel on the end of the spike that the gods stuck through the universe and around which the sky revolves.
To the Moguls (Mongolian empire) it was the peg holding the world together.