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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Peter Mackenzie
Date: 2025 Jan 23, 03:29 -0800
sorry if this is too basic but i'd really appreciate help with this. Here is an example of my query illustrated by part of a question taken from "Astronavigation from Square one" - Alan Murray: "An evening twilight sight was taken of Venus on Tuesday Nov 15th 2011 at 1949 hrs and 37s local time at the chosen latitude of 50º 25' South and longitude 50º 20' West."
What is the correct way to convert the "local time" to UT? Using time zones added to local time? Or, perform Arc to time using longitude?
Do I firstly figure out that the location is in Time Zone +3 and add this to "local time" to get a UT value of 22 hrs 49 mins and 37 secs?
Or, do i work out 50º 20' west is 3hr 21m 20s. Hence UT is 23hr 10m 57s?
i chose the second method (as it seemed more accurate) but the book uses the first. i cannot understand the rationale for using zone time where a specific location is provided and we need accuracy for the subsequent GHA etc calculations.