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    Re: Another sight reduction analog device
    From: Alexandre Eremenko
    Date: 2012 Apr 28, 09:58 -0400

    I found a descrition of astrographs in the Soviet Marine navigation
    manual of of 1971. So they were apparently used at sea, not only
    on the airplanes.
    Soviet astrographs were used without any roling device, just as a pile or
    book of sheets, and they were available only
    for latitudes 42-77 deg.
    The author describes the advantages and disadvantages as folows:
    
    a) simplicity decreases the probability of blunders
    b) the method consimes 2-3 times less time than any tables
    c) no almanac required
    d) no globe required for pre-selecting the stars
    
    And the disadvantages:
    
    1) non-availability for all latitudes
    2) cannot be used for Moon and planets
    3) some loss of accuracy, which is not essential in the open sea.
    (He says that the accuracy is 1' to 1'5).
    
    In a 1989 book of the same author, astrographs are not mentioned.
    (But computers, calculators, and satellites are already mentioned:-)
    A 1979 textbook for navigation schools only mentions the tables,
    (no astrographs, no calculators).
    
    Alex.
    
    P.S. Judging by the number of astrographs on e-bay at a random moment
    of time, the method was quite popular in aviation:-)
    
    
    On Sat, 28 Apr 2012, Gary LaPook wrote:
    
    >
    > Basically it projected the Weems Star Altitudes Curves on to a flat surface 
    for plotting. Since the curves were on a roll of film the device tool up a 
    lot less room than the Weems book of curves.
    >
    > Both of these methods show that the determination on latitude is independent 
    of time, the two altitude curves will always cross at the same latitude. But 
    that intersection moves around the world at 15? 02.46' per hour so you need 
    time to determine the location of the intersection in longitude. Another way 
    to look at it is that crossing two LOPs provide a fix in latitude and LHA 
    Aries and you then use time and the GHA of Aries to convert it to a longitude 
    value.
    >
    > gl
    >
    > --- On Fri, 4/27/12, Alexandre E Eremenko  wrote:
    >
    > From: Alexandre E Eremenko 
    > Subject: [NavList] Another sight reduction analog device
    > To: NavList@fer3.com
    > Date: Friday, April 27, 2012, 6:51 PM
    >
    >
    > It is called an Astrohraph,
    > and the book by M. D. Wright says:
    > "The only mechanical reduction device to achieve wide acceptance
    > was the astrograph".
    > http://www.flightglobal.com/pdfarchive/view/1943/1943%20-%202376.html
    >
    > This it says after discussing the Hagner position finder and
    > citing Weems's opinion on it which more or less coincides with my opinion
    > of such devices which I stated in my previous message, except that I
    > tried to be more polite than Weems:-)
    >
    > Few pages earlier the book however says on Bygrave rule,
    > that "two Britain's most famous navigators, Chichester and D. Bennett
    > relied on Bygrave rule", they mean Chichester as an airplane navigator,
    > of course.
    >
    > Now I recall that astrographs were also mentiones in Soviet navigation
    > books (Marine navigation!).
    >
    > Alex.
    >
    >
    >
    >
    >
    >
    >
    >
    > : http://fer3.com/arc/m2.aspx?i=119297
    >
    >
    >
    
    
    
    

       
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