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    Re: Lunar Distance in Wikipedia
    From: Wolfgang K�berer
    Date: 2007 Aug 22, 15:08 +0200

    D.H. Sadler - one-time Superintendent of HMNAO - says that "the tabulation
    of lunar distances in the Almanac actually ceased in 1906" (The Bicentenary
    of the Nautical Almanac, JIN Vol. 21 (1968), 16). I think that means that
    this was the last time they were published, which coincides with the
    statement by Lecky. Ms. Hohenkerk should know best.
    
    Dr. Wolfgang K�berer
    Wolfsgangstr. 92
    D-60322 Frankfurt am Main
    Tel: + 49 69 95520851
    Fax: + 49 69 558400
    e-mail: koeberer@navigationsgeschichte.de
    
    -----Urspr�ngliche Nachricht-----
    Von: NavList@fer3.com [mailto:NavList@fer3.com] Im Auftrag
    von George Huxtable
    Gesendet: Mittwoch, 22. August 2007 11:16
    An: NavList@fer3.com
    Betreff: [NavList 3129] Re: Lunar Distance in Wikipedia
    
    
    Jim van Zandt and Renee Mattie have both attended to that Wikipedia article,
    
    and between them they are transforming it into something really worthwhile.
    
    I have a few comments, though.
    
    Can anyone see a way to credit Clive Sutherland with that nice drawing? Not 
    that he has any wish to copyright it; he doesn't.
    
    ===================
    
    The article states, under "History",  "Lunar distance tables last appeared 
    in the British Nautical Almanac for 1904, and in the USNO Nautical Almanac 
    for 1912". I don't know about the US version, but have suspicions that the 
    1904 date is a bit out.
    
    Lecky, in "Wrinkles" (actually, a later editor, in my 1917 edition) states 
    on page 758 "The Nautical Almanac for 1907 ... is without tables of lunar 
    distances ..."
    
    May, in "A history of marine navigation", 1973, page 40, states "In 1909 the
    
    Nautical Almanac ceased to publish the necessary tables..."
    
    Hewson, in "A history of the practice of navigation", 1983 ed., page 241, 
    states "... in 1908, lunar distances were omitted from the Nautical almanac"
    
    All three authors were writing from a British background, and would have 
    been referring to the British almanac.
    
    So here we have three authors, all differing from that 1904 date, and from 
    each other! It isn't a vitally important matter, but let's get it right.
    
    Has the British "Nautical Almanac" for those years been digitised, and does 
    any listmember have easy access? It would then be the work of only a few 
    minutes to discover the year of disappearance.
    
    Otherwise, I will ask Catherine Hohenkerk, of HM Almanac Office, who has a 
    complete stack of back-numbers.
    
    ==================
    
    The last paragraph, under "Method", now states- "Knowing Greenwich time and 
    the altitudes of the moon and the other body, the navigator can apply the 
    intercept method to find his latitude and longitude. Alternatively, the 
    navigator can first determine local time, and then longitude.[1]"
    
    That is unarguably true, now, but gives quite the wrong slant, because the 
    first alternative was not generally available in the period we are 
    concentrating on, ending in the mid 19th century. There were two reasons-
    
    First, Sumner's line of position method was not published until 1843, and 
    the intercept method improvements, by St Hilaire, not until the mid-1870s. 
    By this date lunars were in serious decline.
    
    Second, Moon predictions, in terms of GHA and dec, were not provided in such
    
    a way as to allow Moon altitudes to be accurately calculated, in early 
    almanacs. In the 1767 almanac, and for some time after, these quantities 
    were provided only at Greenwich noon and midnight, between which the Moon's 
    declination could change by more than 2 degrees; far too infrequent for 
    proper interpolation. By 1864, the next almanac I have, Moon dec was 
    predicted for each hour, just as in modern almanacs. I don't know when the 
    omprovement took place.
    
    So I think the intercept method should NOT be quoted as the primary method 
    of position finding, to go with a discussion of lunars. Instead, the 
    emphasis should be on direct determination of longitude from difference 
    between local time and Greenwich time.
    
    What do others think?
    
    ================
    
    Under "Errors", there's an explanation of why an error of 1' in lunar 
    distance gives rise to an error of 30' in longitude, and a conclusion "So 
    lunar distance can never be a precise way to determine longitude. After 
    that, someone has inserted {cite}. I wonder why? One follows from the other.
    
    Although I am all in favour of rigour, in presenting evidence for statements
    
    that are made, I feel that this is being unduly pernickety. And I am not 
    convinced that evidence presented in a citation from a book or a journal 
    article is always of value, anyway, as you can see from the contradictory 
    statements, above, about the date of omission of lunar distances from the 
    almanac.
    
    George.
    
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. 
    
    
    
    
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