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    Re: Questions about Celestial Navigation
    From: Frank Reed
    Date: 2018 Sep 11, 10:35 -0700

    Here are copies of my replies (from earlier yesterday) on just the first three questions. I haven't had any time to look at the others.

    Q1: How popular is celestial navigation? Well, it's become quite obsolescent (not entirely obsolete) so the vast majority (e.g. 99.5%) of mariners at sea never use it in the year 2018. On the other hand, on the order of 5% have had some training in it, and it has "popularity" beyond practicality. Everybody loves the idea of it! And probably something like half of all sailors would like to learn how or at least give it a try --if they could find the time. The concept of it is almost magical, and that will never disappear.

    Q2: How trustworthy is it? It's completely "valid" for crossing oceans today. And there's nothing fundamentally wrong with it. But the difference between celestial and electronic (GPS) navigation is huge. GPS is all-weather, while celestial requires clear skies. GPS gives a near continuous position fix updated every few seconds in practical cases while celestial gives a "position fix" only a couple of times daily. And for accuracy, celestial is good to the nearest mile --roughly 500x less precise than a GPS position. Yet what do you need in the middle of the ocean? The limits of celestial on a long passage are really not a serious problem.

    Q3: The tech for celestial is pretty straight-forward (so long as we're talking about normal, manual marine celestial navigation --and there are other cases!). We need an instrument for measuring the angular altitudes of celestial objects, usually a "sextant". We need a really good clock, usually called a "chronometer" in this context, or we need a rather average clock or watch and access to a radio time signal. We also need a database of astronomical information, traditionally this was a book --the "Nautical Almanac". And finally we need some means of performing some secondary school level math calculations including a little trigonometry. Traditionally this was done with books containing mathematical tables but a cheap handheld calculator can suffice today. A navigator doing celestial also needs some paper charts since it doesn't do much good to know your latitude and longitude if you don't know the lats and lons of anything else!

    Frank Reed

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