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
Famous quotes containing the word discovering:
“This is really the common mentality of prisoners: they read with great attention all the articles that deal with illnesses and send away for treatises and “be your own doctor” or “emergency treatments” and end up by discovering that they have at least 300 or 400 illnesses, whose symptoms they are experiencing.”
—Antonio Gramsci (1891–1937)