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Oct 8, 2018

The North Star: facts and myths


Getting a few things straight about our famous guiding star.

The presence of the North Star in our skies is familiar to most people living in the Northern Hemisphere. It sits above the true North Pole, never-moving while the other stars circle round it in a stately carousel. It is the brightest star in the sky, the one that has forever and will always point northwards…

So, who spotted the deliberate errors in the opening paragraph? There’s quite a few. Surprisingly, though, many people do believe them to be true. This is perhaps a symptom of our disconnectedness with the glories of the night sky in our light-polluted world. We no longer rely on the North Star and its companions to guide us on our way across oceans and continents – we have satellites and sat-navs for that. Nonetheless, let’s put a few of those myths to rest.

  • Well, the North Star does lie above the true North Pole, and remains pretty much at a fixed point in relation to the other stars circling round its position…for now. Also called Polaris, or the Pole Star, it hasn’t always pointed north, and eventually yet another star will oust it from its throne. A pole star is one that is aligned to the axis of rotation of a planet, but the Earth’s axis “wobbles” in a circle, like a spinning top, in a timeframe of about 26,000 years (this is called precession). So, over this period, the axis will point towards different stars. Go back 5,000 years (to 3,000 BCE) and Thuban (in the constellation Draco) was the Pole Star. Go forward about 2,000 years to 4,000 CE, and it will be Gamma Cephei (in the constellation Cepheus).
  • Viewed from Earth, Polaris is only a moderately bright star (as is Gamma Cephei; Thuban is also not particularly bright). The brightest star in our sky (other than the Sun, of course!) is Sirius (in Canis Major; Sirius is from the Greek for glowing), due to a combination of its luminosity and relative closeness to our solar system.
  • Polaris is not a single star – along with Sirius and future pole star Gamma Cephei, it is a binary star system. Previous pole star Thuban is a blue giant.

How to find the North Star

Polaris is in the constellation Ursa Minor (The Little Bear), but you can locate it best by first finding the easily recognisable, saucepan-shaped Ursa Major (The Great Bear or Plough, or Big Dipper in the USA). Take the two stars at the side of the ‘saucepan’ furthest from the ‘handle’, and draw a line from them until you reach Polaris (see diagram).

Where can I go to try this out?

Anywhere with reasonably low levels of light pollution. There are several good places to stargaze on Cranborne Chase AONB.

Is there a Southern Pole Star?

No – it’s pure chance that we have a star aligned with the Earth’s axis at the North Pole.

References:

Gooley T (2014) The Walker’s Guide to Outdoor Clues and Signs. Hodder & Stoughton, UK.

Moore P (2001) Stargazing (second edition). Cambridge University Press, UK.

 

Image attribution: By NASA/HST [Public domain], via Wikimedia Commons