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    Re: Nautical Almanacs
    From: George Huxtable
    Date: 2010 Nov 25, 13:54 -0000

    Henry wrote-
    
          "I have completed downloading and chronologically arranging by
    intended year of use copies of The American Ephemeris and Nautical Almanac
    for the years 1855 through 1920, all inclusive. Anyone desiring a copy of
    this publication for any year within the range indicated may email me off
    list and I shall be pleased to forward the same - each file running between
    about 20 and 30 MB. I am currently working on a similar downloading of the
    British counterpart to the American and have completed about 60 downloads,
    commencing with 1767.
    
          I fully realize that these pubs are generally available on the
    internet, however, have found them to be inconsistently or even erroneously
    identified, generally by year of publication as opposed to year of intended
    of use. When working with old texts or logbooks, I now have the relevant
    Almanac immediately at hand - it works for me."
    
          ============
    
          Bravo, Henry! That's quite an undertaking. Especially if Henry is
    offering to be some sort of distributor of such Almanac information, which,
    as he says, is by no means simple to access.
    
          I am specially interested in these words-
          "I am currently working on a similar downloading of the British
    counterpart to the American and have completed about 60 downloads,
    commencing with 1767."
    
          First, a bit of a quibble, in my usual vein. Isn't it a bit
    Americo-centric to refer to the British almanac as "the British counterpart
    to the American...", when it preceded it by many years, and the American
    version commences life by wholesale copying from the British?
    
          But, more seriously, if Henry's project has taken him far enough, I
    would welcome copies of any relevant Almanacs he can provide covering the
    years 1803 and 1804, the first two years of the Lewis and Clark journey
    across America, some aspects of which I have studied in detail.
    
          ==============
    
          And Frank added-
    
          "I've been assembling a table of the typical error (s.d.) of the
    published lunar distances compared to their known values from modern
    ephemerides. What I have is mostly sufficient for that but I'm particularly
    interested in the changes through 1820. "
    
          That, too, seems a worthwhile project, and many of us would be
    interested in its results.
    
          I wonder, however, if a simpler analysis would provide useful
    information. Printed errors in lunar distance involve errors in the
    following-
    
          1. The predicted position (in celestial lat and long) of the Moon, at
    Greenwich noon and midnight.
          2. The predicted position (in celestial lat and long) of the Sun or
    star (or, later, planet).
          3. Interpolating those predictions to a Greenwich time, at 3-hour
    intervals (by a 4-point non-linear fit, for the Moon).
          4. Calculating a great-circle angle between them.
          5. Any subsequent blunders in transcribing or typesetting that were
    not picked out in time for an erratum slip.
    
          It seems likely to me that the overall error will be dominated
    completely by item 1, compared to which the others are all negligible. I
    don't KNOW if that's the case, however, and have made no efforts to test
    it.
    
          Right from 1767, the predicted ecliptic latitude and longitude of the
    Moon, at Greenwich noon and midnight, were tabulated; given, somewhat
    optimistically, to the nearest arc-second.
    
          It strikes me that if those predictions were collected, over a long
    period, and compared with modern Moon predictions, the differences could be
    very informative, especially when plotted in terms of the Moon's  phase,
    declination, and nodal cycles. I have never got involved in such a study,
    partly because of the difficulties, in the past, of collecting that Almanac
    information (and partly, I admit, due to a certain natural indolence). I
    don't know if anyone has made such a study, but haven't heard of it.
    
          I understand that the Moon predictions in the American almanac became
    more accurate on account of their earlier adoption of Brown's lunar theory.
    It would be interesting to see how that worked out in practice.
    
          Greenwich astronomers, as I understand, from time to time, analysed
    past lunar predictions by comparison with their recorded observations of
    the same meridian passage, but I've never seen the results of any such
    study or even discovered a reference to it. If anyone knows of such
    reports, I would be most interested.
    
          George.
    
    
    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "hch" 
    To: 
    Sent: Thursday, November 25, 2010 3:42 AM
    Subject: [NavList] Nautical Almanacs
    
    
    | To all,
    |
    | I have completed downloading and chronologically arranging by intended
    year of use copies of The American Ephemeris and Nautical Almanac for the
    years 1855 through 1920, all inclusive. Anyone desiring a copy of this
    publication for any year within the range indicated may email me off list
    and I shall be pleased to forward the same - each file running between
    about 20 and 30 MB. I am currently working on a similar downloading of the
    British counterpart to the American and have completed about 60 downloads,
    commencing with 1767.
    |
    | I fully realize that these pubs are generally available on the internet,
    however, have found them to be inconsistently or even erroneously
    identified, generally by year of publication as opposed to year of intended
    of use. When working with old texts or logbooks, I now have the relevant
    Almanac immediately at hand - it works for me.
    |
    | Regards,
    |
    | Henry
    |
    |
    |
    |
    |
    
    
    
    
    

       
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