This Word Means: North star

Guide to navigation

Polaris, known as the North Star or Pole Star, is a very bright star — around 2,500 times more luminous than the Sun. It is part of the constellation Ursa Minor, and is around 323 light years away from the Earth.

Since Polaris is less than 1° away from the north celestial pole, almost in direct line with the Earth’s rotational axis, it appears to sit motionless in the northern sky, with all the other stars appearing to rotate around it.

Its position and brightness have allowed humans to use it for navigation since late antiquity. Simply the elevation of the star above the horizon gives the approximate latitude of the observer. In the northern hemisphere, if you can spot Polaris, you can tell the north — and by extension, the other three directions as well. Upon crossing the equator to the south, however, the North Star is lost over the horizon, and hence stops being a useful navigational aid.

Ptolemy and Columbus

Polaris seems to have been first charted by the Roman mathematician and astronomer Ptolemy, who lived from about 85 to 165 BC. While there is some evidence that the star was used for navigation in late antiquity, it was during the ‘Age of Exploration’ that it became a central part of human history.

Christopher Columbus, on his first trans-Atlantic voyage of 1492, “had to correct (his ship’s bearings) for the circle described by the pole star about the pole”, and the star became an invaluable aid to the European colonists seeking out far-off lands across the seas.

Literary metaphor

The first well known instance of the North Star appearing in literature outside of a technical treatise on astronomy or a biography of an explorer is in Shakespeare’s Julius Caesar, where the eponymous emperor describes himself as being “as constant as the Northern Star”.

However, the “constant” North Star was probably not known to the real Caesar (reign 49-44 BC). Also, as the NASA page on Polaris points out, “North Star” is “a title that passes to different stars over time”. As the Earth’s axis of rotation wobbles in the same way as a spinning top, the celestial pole “wanders in a slow circle over the eons, sweeping past different stars”. About 14,000 years ago, the celestial pole pointed towards the bright star Vega, and “it will again point to Vega in about 12,000 years”.