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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2023 Mar 10, 05:58 -0800
Ed,
The way the NA was used to determine GMT via Raper's method is described in detail here https://www.canterburymuseum.com/assets/DownloadFiles/Navigation-of-the-Shackleton-Expedition-on-the-Weddell-Sea-pack-ice.pdf . More efficient and elegant is Bessel's method that can be found in the Explanatory Notes in the back of old editions of the NA or in W. M. Smart's Spherical Astronomy. In both methods the key inputs are latitude and local mean time (LMT).
These methods are designed to be practical for manual calculations. Nowadays we can take a much more boneheaded approach. Suppose I have at my disposal a function takes latitude, longitude and GMT as inputs and returns the topocentric position of the Moon.
Function MoonPos( latitude, longitude, GMT)
Call this function with arguments MoonPos( latitude, 15*(LMT-GMT) , GMT ) and adjust GMT until the topocentric position of Moon is 1 (topocentric) lunar semi-diameter (SD) from the occulted star,
Regards,
Robin
