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Meridian altitude of the sun (Lesson 2)
25 October 2023 · 10 min · 3K views
What this video covers
Calculating latitude via celestial navigation requires measuring the sun’s altitude at local apparent noon using a sextant.1:05 This method relies on the sun’s declination, a value found in the nautical almanac that varies throughout the year due to the 23-degree, 26-minute tilt of the Earth’s axis relative to the ecliptic.1:42 To determine latitude, a navigator first calculates the zenith distance, defined as 90 degrees minus the observed altitude of the sun.4:17 In the northern hemisphere, latitude is the sum of the declination and the zenith distance.4:50 When the observer's latitude is lower than the sun's declination, the formula adjusts to declination minus the zenith distance.6:54 Because the sun reaches its highest point at local noon, this observation does not require a high-precision clock.9:11 Navigators must apply small corrections for parallax, also sourced from the nautical almanac, to account for the sun’s distance from the Earth.3:07
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