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    Re: Precession and Nutation
    From: Mike Freeman
    Date: 2017 Jan 31, 06:37 -0800

    Thank you David & Stan,

    A few things of which I was unaware, am now. The book I am studying (Celestial Navigation for Yachtsmen, Mary Blewitt 1990 edition) suggests when using Polaris or Planet in conjunction with Stars to move each Stars LOP by the amount in AP3270 Vol 1 Table 5. Rather than move Polaris. Possibly 6 of one half a dozen of the other?. It does also suggest the a0 a1 a2 as in Davids second post.

    Initially I became interested in Precession and Nutation because I assumed, possibly incorrectly that the corrections in Polaris tables in NA and the corrections in AP3270 Vol 1 Table 5 were both for precession and nutation, although this is only made clear in Polaris tables. However the reason I became confused is entering argument for Polaris tables is MONTH and entering argument for AP3270 vol 1 Table 5 is YEAR. 

    I also assumed possibly correctly on this occasion Precession & Nutation already taken into account for Sun, Moon & Planets when calculating GHA and Declination from the NA.

    What is not clear is whether any element of P & N is taken into account when calculating GHA Aries. At the moment I am thinking this is why entry arguments for Polaris tables and AP3270 vol1 Table5 differ in respect of MONTH or YEAR.

    Obviously I understand all the information contained in the NA and AP3270 Vol 1 will have changed since my book was published in 1990 but providing the method has not changed I am pretty happy that the application is pretty well explained it is just that I became curious about the MONTH/YEAR anomaly.


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