In high latitudes, the observation of the sun for checking compass error by the Amplitude Method is unreliable.
In high latitudes, the path of the sun is very low as a result of which it follows a very long path from the visible horizon to the sensible horizon and thus, the rate at which the body is changing its azimuth is comparatively large. Consequently, a small change in altitude results in a large change in azimuth. This makes the accuracy of the observation unreliable; unless the observer could be precise regarding the time that the body’s centre is on the sensible horizon.
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When checking compass error by the amplitude method, state the correct position of the sun in relation to the visible horizon.
When observing the amplitude, the centre of the observed body should be on the celestial (sensible) horizon of the observer. But the visible horizon does not coincide with the celestial horizon because of the combined effects of refraction, parallax and dip.
Thus, when checking compass error by amplitude method, the lower limb of the sun must be semi-diameter above the visible horizon whereby the sun’s centre will be at the celestial horizon.