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Celestial Navigation and the Single Star

Presentation #304.05 in the session Computation, Data Handling, Image Analysis.

Published onJul 01, 2023
Celestial Navigation and the Single Star

Celestial navigation is the fine art of getting from here to there using the stars, the naked-eye planets, and the Moon. Homer writes of the sailing directions referenced to constellations that Calypso gave Odysseus. Pacific Island navigators observe stars along with sea and sky conditions to find their way. Even with the sophisticated navigational technology available today, celestial navigation remains an important, independent means of emergency navigation.

Celestial navigation training using the intercept method of St. Hilaire returned to the US Naval Academy in 2015. Working from an assumed position, this technique uses the measured altitude (height) of two, preferably three, bodies relative to the horizon along with the associated times. By comparison with the associated tabulated geographical position (terrestrial position directly below the celestial object), each sighting results in a line of position along which the observer may be situated. The intersection of multiple lines eliminates the ambiguity. Alternatively, latitude and longitude can be determined by observing the altitude and the time at which the celestial body, usually the Sun, crosses the observer’s meridian.

Jablonski and Homeier (2022) propose observing both the altitude and azimuth of a celestial body. The observer’s latitude and longitude can then be computed using the tabulated Greenwich Hour Angle (GHA) and declination for the body at that same time. Like other celestial navigation techniques, sources of error include the altitude and azimuth angles, the observation time, and the identification of the body, when fainter stars or planets are used.

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