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    Re: Time of meridian passage accuracy
    From: Peter Hakel
    Date: 2009 Sep 25, 15:19 -0700

    From: George Huxtable <george@hux.me.uk>

    On the 29th April, the Sun's declination is increasing
    (Northward) by about 0.8 arc-minutes per hour.


    If we define:

    d: hourly rate of change of Sun's declination in arcminutes
    D: number of days elapsed during the current year
    a: "phase angle" ( a~0 at winter solstice, a~90 at vernal equinox, etc. )

    a = {D+10} / 365 * 360 degrees

    then the following approximate expression for "d" seems to work well enough:

    d = 60 * 23.45 * SIN(a) * ( 360 / 365 ) / 24 * ( Pi / 180 )

    For April 29 we have D=118 and hence d=0.8' per hour, just as George stated above.

    Peter Hakel

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