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Published online by Cambridge University Press: 23 November 2009
For a long while now positions on the surface of the Earth have been fixed by observing the altitudes of two heavenly bodies. The equations:
include on their left-hand side two observed zenith distances and on their right-hand sides the required values of latitude and longitude. The history of celestial navigation records many different solutions to the problem, one of them being the observation of equal altitudes of the same body east and west of the meridian, usually the Sun, or of two different stars. If only the local time is required it is not even necessary to measure the exact altitude.