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    From: Mike Freeman
    Date: 2018 Feb 20, 10:14 -0800

    Just learning and wondering if this is a reasonable summary.

    There are 63 heavenly bodies and a GP is provided for each one in the Almanac for every second of the year. That adds up to nearly 2 billion GP's expressed as GHA and Declination. Additionally the terrestrial sphere has 64,800 pre determined positions at the intersections of the whole degrees of Lat and Long (360 x 180). These are known as assumed positions. From these AP's the altitude and azimuth of each of the 2 billion possible GP's of the HB's have been calculated (Hc) and are published in sight reduction tables such as AP3270 (Ho249). Obviously not all HB's are visible at one time and in the case of AP3270 Vol1 the Hc and Zn of 7 selected stars only, applicable to your vessels location (DR Lat and LHA Aries). A LOP is derived by plotting an azimuth on a plotting sheet and by calculating an intercept by comparing Ho with Hc. 1 minute difference equals 1M towards or away. Need to carefully extract data from the almanac & tables and add or subtract as required.

    I would be pleased to be advised of anything I have misunderstood.

    Thanks Mike

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