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    Sight reduction tables
    From: George Huxtable
    Date: 2007 Sep 28, 23:43 +0100

    John Karl asked-
    "Which brings me to the one question I asked in the book that I can't figure
    out myself:  Why are the tables in H.O. 249 and H.O. 229 ordered
    differently?  I much prefer H.O. 249's order because latitude changes slowly
    at sea, while we're always skipping around in LHA."
    And Gary LaPook added-
    "That is the same question for which I have never gotten an answer. The
    arrangement of tables in H.O.249 and H.O. 214 is much more convient, often
    allowing you to do the entire round of sights with only one book opening.
    So who's bright idea was it to use LHA instead of latitude in H.O. 229?"
    Comment from George-
    I don't know anything about HO 229 and HO 249 except what I have read about
    them in Dutton's, and that ignorance may become apparent here. All I have
    been familiar with is their predecessor, HO 214, in its British vesion.
    But I wonder whether HO 249 is as quite as convenient as has been made out.
    True, it seems to me, if you're just doing a round of star-sights with the
    choice of seven stars as listed in vol 1, they are all to be found together.
    But then, if you want to add a planet, or the Moon, with HO 249 you seem to
    have to switch, not just to another page, but to quite another volume, 2 or
    3 depending on your latitude, and then these different bodies (or a
    low-declination star) may require a scan of different, but closely spaced,
    pages. Have I got that right?
    Of course, HO 249 achieves its condensation by sacrificing precision,
    working only to 1 minute instead of 0.1 minutes. And that allows the chosen
    stars to have fixed positions, whereas aberration alone can shift some stars
    by up to 0.3' each way, over a year. But it leaves another question in my
    mind. How does HO allow, for its named stars, for the slow drift in star
    position caused by precession? Is there some way provided of correcting for
    this drift, year on year? Or is Vol 1 of HO249 reissued after a period, when
    precession starts to put star positions unacceptably far out?
    contact George Huxtable at george---.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    To post to this group, send email to NavList@fer3.com
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