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    Re: Longitude at noon
    From: David C
    Date: 2020 Sep 8, 21:24 -0700

    Frank wrote

    So why don't books on celestial navigation make this simple process more clear? That's a question worthy of some discussion and speculation!

    Old navigation text books were recipe books - they gave the steps to follow to obtain the result. If you wanted to understand the method then you often had no option but to work through the example, determining where each number came from.

    In modern times maybe it is considered too "obvious". No matter what reduction method you use you must calculate LHA = GHA +- long. If LHA=0 then GHA=long.  All due respects but someone who does not understand this cannot understand CN.

    In a book first published in 1914 Brent describes a method for determining noon long from two ex-meridian sights. The formula is derived in detail but it is left to the reader to infer how longitude can be determined from the formula.  In the attached notes you will observe that using this method I determined my long from two near-noon sights to within 8.5'. It took me  some time to work out the process.

    It is important to note that I am a 21st century armchair navigator. Someone who was taught and who practised navigation at the end of the 19th cenrury  may find Brent's explanation obvious.



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