Part 2(2): The Quick Course to Celestial Navigation
7 de julio de 2023 · 31 min · 3K visitas
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Celestial navigation requires comparing an observed altitude (Ho) of the sun, measured with a sextant, against a pre-calculated altitude (Hc) derived from sight reduction tables.1:20 To perform this calculation, a navigator must determine the sun’s declination and Greenwich Hour Angle (GHA) using an astronomical almanac and a precise clock.4:11 Because sight reduction tables are printed for full degrees of latitude and Local Hour Angle (LHA), the navigator selects an "assumed position" near their estimated location that satisfies these whole-degree requirements.9:51 The difference between the observed and calculated altitudes provides the "intercept," a distance in nautical miles that defines a position line relative to the assumed position.13:55 By plotting two such lines—often taken at different times and adjusted for the vessel's movement—a navigator establishes a fix.17:03 While manual calculation using almanacs and tables is standard, digital apps can also generate the required Hc and azimuth values.21:05
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