Yourbestsail · video

What this video covers

Celestial navigation relies on the method of intercept lines to determine a vessel's position by calculating the difference between an estimated altitude and the true altitude of a celestial body.0:04 Navigators use a sextant to measure the true altitude above the horizon and a nautical almanac to determine the body's coordinates.0:22 By assuming an estimated position, a navigator calculates the expected altitude and azimuth using spherical trigonometry.3:42 The difference between the true and estimated altitude provides the distance to move from the estimated position to the line of position.3:30 Intersecting two such lines from different celestial bodies fixes the vessel's location.7:00 The derivation of these formulas involves the spherical law of cosines and the law of sines, which relate the sides and angles of a spherical triangle.11:52 While Spanish nautical almanacs often require electronic calculators to solve these equations, British tables utilize logarithms to perform the same calculations manually, maintaining independence from electronic systems.59:45 Understanding the mathematical derivation of these formulas clarifies the underlying principles of celestial navigation.

More from Yourbestsail

The genoa sheet car (Again!)Sept 2026The function of the centerboardAug 2026Marinas and Yacht Clubs: ProceduresAug 2026The 10 most common mistakes when docking a boatJun 2026

From Yourbestsail — see the channel’s boat, crew, and every analysed video.

The Sailing Directory Newsletter

One email with the fleet's best finds — the moments, boats, and stories worth your watch time. Enter your own address to get your own copy.