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    Re: Time balls
    From: Robin Stuart
    Date: 2021 Oct 5, 13:33 -0700

    Tony,


    Time balls are not dropped at LAN. That wouldn't provide any useful information that was not available by other means. Local Apparent Time (LAT) is determined via time sight by sextant observation. LAN can be determined by equal altitudes of the Sun as I discussed here http://fer3.com/arc/m2.aspx/Longitude-Equal-Altitudes-Stuart-jul-2020-g48277

    Time balls were typically dropped at 1PM LMT for some standard meridian and allowed the chronometers to be reset or the current chronometer error (CE) to be determined. For example the time at Buenos Aires was dropped at 1PM for Argentina's standard meridian through Córdoba, see http://fer3.com/arc/m2.aspx/Time-balls-Stuart-dec-2019-g46490

    Apparently 1PM was the standard as the astronomers were too busy at noon.

    David C,

    I would guess the signal cannon on Mt. Victora was mostly intended for low precision civil use. If you just went by the bang and didn't allow for your distance from it, each mile away would introduce a 1.2' error in longitude. You could get around this by loading some phosphorus or magnesium powder in with the charge to make a visible flash but I'm not sure how happy the local fire brigade would be about that,

    Regards,
    Robin

       
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