Polaris (aka the Pole Star) stands in the sky vertically above the North Pole (not quite exactly, but near enough). That means that if you were at the North Pole during the long Arctic night and looked directly overhead you’d see Polaris. And if you were anywhere else in the northern hemisphere, facing towards Polaris, you would be looking due north (true, not magnetic). Though, as I explain in the video, thanks to the phenomenon of ‘precession’, this would not always have been the case, nor will it be in the not-too-distant future.

If you know where true north is, you can set a course in any direction. No wonder Polaris used to be called ‘Stella Maris’ - or the ‘star of the sea’. In the Middle Ages, the same term (which can also be translated as ‘the star of Mary’) was applied to the Virgin Mary, whose sky-blue cloak is emblazoned with a star in many medieval paintings. Mary was likened by the theologian Alexander Neckham (1157-1217) to the Pole Star, standing at ‘the fixed hinge of the turning sky’ by which the sailor at night directs his course. As I wrote in SEXTANT, ‘Polaris must have seemed a perfect symbol for the Mother of God, the immaculate spiritual guide and intercessor’.

But, as I explain in this video, birds are not human and they don’t use Polaris. Instead, they wisely attend to the rotational pattern of stars around it - something on which they can always count. To illustrate this, here’s a long-exposure photograph of the northern sky in which you can see the circular paths traced by each star. Polaris itself appears as a stationary dot at the centre of the pattern. The same principle would also work in the Southern Hemisphere, which is handy because there is no southern equivalent of Polaris: the southern celestial pole lies in a rather blank patch of sky, at least for the present!