Learning Celestial Navigation - The Marine Sextant - How to master Astro Nav!
25 February 2024 · 7 min · 2K views · Martinique
What this video covers
A marine sextant measures the angle between a celestial body and the horizon using an index mirror, a horizon mirror, a telescope, and a micrometer drum.0:13 The index arm provides gross adjustments, while the micrometer drum allows for fine-tuning to the tenth of a minute.1:03 One minute of arc on the sextant corresponds to one nautical mile of accuracy.1:30 To measure the sun, the user selects appropriate shades to protect the eyes and targets the sun’s lower limb, balancing it on the horizon.3:39 The operator brings the sun down to the horizon by moving the index arm while simultaneously lowering the sextant, then swings the instrument in an arc to ensure the sun’s lower limb just touches the horizon at the lowest point of the swing.5:37 Accurate celestial navigation requires recording the precise time to the second alongside the measured angle.6:04 Practice at anchor or with an artificial horizon builds the necessary proficiency for use at sea.7:20
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