Determining Latitude using Polaris (the Pole Star)
Most of us are aware of the significance of the Pole Star (North Star), correctly called Polaris.
It sits over the North Pole, on the axis of the earth. In the Northern hemisphere we are very lucky, as it will always shows us where true north is (providing the sky is clear!)
But there is more to Polaris than showing us north. Consider the diagram below;
Imagine we are standing on the North Pole. The Pole star is directly above our heads, our icy horizon disappearing away all around. Imagine we have brought our sextant and we measure the angle between our horizon and the Pole Star, what angle will it give? Hopefully it is fairly obvious that the sextant will read 90° as Polaris is right above our head. Now imagine we have jetted off to Ecuador (or somewhere else on the Equator). Again, we measure the angle between our horizon and the Pole star. This may not seem so obvious, and diagram may be misleading, but remember the Pole star is light years away and that all rays of light from it are travelling as parallel lines. Therefore, the Pole star will be right on the horizon, giving a sextant angle of 0°. Walk one step into the southern hemisphere and the pole star will disappear from view.
Now, if we are standing at the Equator, what is our Latitude? 0° you say. And if we at the North Pole, what is out Latitude? 90°N you say. So if I am standing in Falmouth, UK and my sextant reads 50°09’, what is my Latitude? Hopefully 50°09’ N is your answer.
How cool is that!
So, the Pole star is a very useful celestial object, it has been known of, and used by the ancient mariners for millennia. It is one of our main traditional methods used to find Latitude.