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    Re: Time of Sun & Moon rise and set
    From: Frank Reed
    Date: 2016 Feb 5, 21:01 -0800

    Brad, you wrote:
    "The sun has a maximum rate of change in declination of 0.1 minutes of arc per hour."

    Looks like you moved a decimal point somewhere. I like to remember that the Sun's "speed" in latitude is very nearly one knot on the equinoxes --or 1.0 minutes of arc per hour (in longitude on the equinoxes, it's 15° per hour, which is nearly 900 knots, by the way). We're still only talking about one knot rate of change in latitude (=declination) so if you were trying to determine longitude by symmetry of sights about local noon, the correction would still be relatively small. In other words, not much difference between time of meridian passage and time of culmination. The nominal correction to longitude gets larger rapidly as we approach the poles, but if you convert that into miles in the fix, the problem is much reduced since longitude lines are closer together at the poles. Convenient that.

    By the way, I'm pretty sure that this was not what Steve Bryant was asking about. Time of meridian passage does not depend on latitude. That answer still stands.

    Frank Reed
    Conanicut Island USA

       
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