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    Re: Silicon Sea Leg 88 questions
    From: Peter Fogg
    Date: 2004 Feb 4, 16:18 +1100

    Renee Mattie wrote
    
    > I also have (for
    > Long 153d 54.8' W
    > LAT   038d 46.1' N
    > 2002 Sep 9 22:12:34 UT)
    >
    > GHA 153d 50.'
    > DEC 005d 06.8'
    > Hc 055d 20.7'
    > Azimuth 179.9d
    > >From the National Observatory website.
    > Which gives me
    > Intercept 22.8 nm AWAY
    >
    > The big difference here is DEC
    
     Renee, there seem to be 2 inconsistancies, the DR latitude which you stated
    earlier as
    >5) arrive at DR #2 39d46.1'N 153d54.8'W, at 22:12:34 UT,
    and the date, 39 hours after the 9 Sep DR. The declination is accurate for
    the 9 Sep.
    
    > I do not have another reference for GHA & DEC
    > for 2002, so I put my faith in the national observatory.
    > Where did you get your data?  Which do you trust?
    and
    > I've seen several good suggestions in the DIY plotting charts
    > thread that sprang up from my questions.  Do you have more?
    
    One answer to both:
    I use a book called 'The Complete On-Board Celestial Navigator'
    It has 5 years of almanac data and not only blank plotting sheets but worked
    out examples showing how to reduce a sight and plot it,
    and much else besides.
    
    Celestaire may stock it http://www.celestaire.com/
    
    or you can find it at Amazon, this link is fairly long
    
    http://www.amazon.com/exec/obidos/tg/detail/-/0071396578/qid=1075868757/sr=1-1/ref=sr_1_1/002-9746912-6430441?v=glance&s=books#product-details
    but leads to more information, reviews, etc.
    
    Just by the way,
    
    > For part 5 of Leg 88, we are within a 10th of a minute.
    > Hs 054d 48.1'
    > IC -000d 02.5'
    > Dip -000d -3.0'
    > Ha  054d 42.6'
    > Ac  000d 15.3'
    > Ho 054d 57.9'
    
    One value, the altitude correction, is more accurate than my approximation,
    but your dip correction is the other way around.
    For dip one solution is to use a simple table, where -3' applies to all
    heights of eye between 6 and 13 feet.
    Another is the formula: square root of height of eye x .97 (for feet) or
    1.76 (for metres)
    So here with height eye of 9 feet: 3 x .97 = 2.91
    
    > You said that you wanted to check your results against the "official"
    > answers.  As far as I can tell, they have not been published.
    > Dan Hogan has stated that he currently has higher priorities.
    
    Well, that's sad news. Perhaps they'll turn up in the fullness of time.
    We live in hope.
    
    
    

       
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