Discovering Declination
An unknown declination can be discovered on location at that moment in time by reference to the celestial poles, the axis of circular motion of stars traversing the night sky.
In the northern hemisphere, if you can see Polaris (the North Star) the declination can be determined as the difference between the magnetic bearing and a visual bearing on the polestar. Polaris currently traces a circle 0.75° in radius around the north celestial pole, so this technique is accurate to within a degree. At high latitudes a plumb-bob is helpful to sight Polaris against a reference object close to the horizon, from which its bearing can be taken.
Read more about this topic: Magnetic Declination
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