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    Re: Nautical astronomy was different
    From: Frank Reed CT
    Date: 2004 Oct 19, 21:56 EDT
    Bruce S wrote:
    "(1) A lunar distance didn't give you the time. It couldn't. What it did was give you the longitude, so you could correct the dead reckoning. "

    It gives "a" time. Lunars typically gave Greenwich Time. I think you're trying for an eccentric point of view here, perhaps, as you put it, to stir a little controversy. But historically I don't think navigators had any problem with the idea that lunars did, in fact, yield time as their penultimate result. They yielded Greenwich Time and comparing that with local time (derived from a time sight) gives longitude.

    And:
    "(2) A chronometer, set to GMT, didn't give you the time either. Not unless it had been "regulated" with a time sight. Like a lunar, it gave you the longitude. "

    Quite eccentric. You state as a given that it's "set to GMT" but then say that it doesn't give time. Since when is time not time?? Is this approach to the subject designed to confuse students of navigation, or is that just an accidental by-product?

    And:
    "(4) You had no need of accurate Greenwich time when taking out data for working observations. A crude estimate did the job. "

    That's a matter of degree, of course, but essentially true.

    And:
    "(5) As a navigator (as opposed to an astronomer) you needed very little from the Nautical Almanac beyond the predicted lunar distances. If you'd been able to rely on a chronometer you probably wouldn't have bothered with an Almanac. Your navigation manual had all the astronomical data you were apt to use."

    Yes, you can get by without a Nautical Almanac. For what it's worth, it's possible to sail around the world doing celestial with nothing but a cheap sextant, an analemma, and an inexpensive (modern) watch. Possible... but where's the challenge in that?

    So in the latter half of the 19th century, when chronometers were universal but the "old navigation" was still practiced, why would a navigator carry a Nautical Almanac? Mostly because it provided alternatives (data for the planets, e.g.) and some modest improvements in accuracy for sun sights. But to reiterate, it is true that you can get by without an almanac.

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
       
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