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    Re: A noon sight conundrum
    From: Herbert Prinz
    Date: 2003 Nov 30, 13:17 -0500

    Pierre Boucher wrote:
    
    > 12h 06m is the meridian passage time at the ZM (Zone Meridian) i.e. at 135d
    > 00.0'E
    >
    > Difference of longitude between the ZM and the observer's meridian is 2d
    > 20.0' west of the ZM
    > Converted to time this gives 9m 20s (later because west of ZM)
    >
    > So  12h06m +  9m20s = 12h15m20s
    > Bear in mind that the meridian passage times tabulated in the almanac are
    > rounded to the nearest minute.
    
    True, but the equation of time is tabulated in seconds right next to it. That
    renders the time of meridian passage completely redundant. It seems to me that
    its only purpose is to eliminate the mental circus act of figuring out whether to
    add or to subtract EoT from 12:00.
    
    Indeed, EoT, nowadays and hereabouts being the correction to be added to mean
    time to get apparent time, is negative on Jul 20 - as indicated by the shaded
    background. Since we want to go from apparent to mean we have to subtract it from
    12:00 But subtracting a negative value means adding its magnitude. Thanks
    goodness, we can forget all this. First we look to the right side and see
    meridian passage is at ca. 12:06 UT. Then we look to the left and find that it
    actually happens at 12:06:19. At other times, when we see a meridian passage
    around 11:xx UT, we know that we have to subtract EoT from 12:00.
    
    I find this still cumbersome. Would it not be much easier if the nautical almanac
    would dispense with EoT altogether and just give the sun's upper and lower
    meridian passage through Greenwich in UT to the second?
    
    Herbert Prinz
    
    
    

       
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