Celestial Navigation with a Sextant - Introduction
12. november 2023 · 5 min · 13K visninger · middle of the Atlantic Ocean
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Celestial navigation provides a reliable backup for offshore positioning when GPS systems fail or chart plotters malfunction.0:12 The process requires a sextant to measure the angular distance between the sun and the horizon.1:30 Two primary methods exist for calculating position from these measurements: the meridian passage and the intercept method, or "droite de hauteur."1:53 The meridian passage offers simplicity, requiring only a sextant, a watch, and current nautical almanacs to determine latitude and longitude at local solar noon.2:12 However, this method fails if cloud cover obscures the sun at the exact moment of the zenith.2:25 The intercept method allows for measurements at any time of day, making it more flexible during overcast conditions.2:45 This technique requires additional navigation tables like the HO 249, along with precise tracking of the vessel's average heading and distance traveled between multiple sightings.3:50 While the intercept method demands more time for manual calculations at the chart table, it ensures a position fix regardless of the sun's specific altitude.3:50
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