How to find your latitude from Polaris (otherwise known as the Pole Star or North Star).
Assume that the Pole Star (Polaris) is exactly in line with the Earth’s axis produced, as shown in the following diagram.
To an observer O on the Equator (lat. 0o) the Pole Star will be in line with the horizon, i.e. it will have an angle of elevation or altitude of 0o.
1. The Pole Star is slightly offset from the Earth’s axis but for the purposes of this exercise, we can assume that it is in line without any great loss of accuracy.
2. Because of the great distance of the Pole Star from the Earth, we can also assume reasonably that the horizon corresponds to the Earth’s axis.
If the observer (O) were to move 60 n.m. due north from the Equator to a latitude of 1oN, then the altitude of the Pole Star will obviously increase to 1o (i.e. it will now be 1o above the horizon) as shown in the diagram below.
From this, we can see that, in the northern hemisphere, the altitude of the Pole Star corresponds to the latitude of the observer. So, if a navigator measures the altitude of the Pole Star and finds it to be 45o, then he can conclude that he is at latitude 45oN.
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