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    Lat and Long by moon transit.
    From: Jeremy C
    Date: 2011 Jan 28, 11:06 -0500
    I attempted a moon fix around transit during my big cruise in 2009. It worked okay. 
     
    I once did a Lat/Long at transit for Venus during the day.  The Longitude actually came out better than the Latitude, but that was probably an anomaly.
     
    The moon is a fickle creature and not for the newly initiated in Celestial Navigation. 
     
    Here's moon data if anyone wants to play (I'm not sure if I ever posted this one.)  As you can see we are moving at a decent speed near South so there will be a displacement of the curve.  The declination is about 7 degrees south and increasing by about 14 minutes/hour so the displacement should be somewhat minimized.
     
    Moon Lines near Transit Crs 193 True
    Spd 13.5 knots
    Date: 30-Jun-09 1900 DR Lat 21-58' North
    GMT Hour GMT Minute & Sec HS deg HS minutes DR Long 130-08' E
    09 39-40 55 18.8 1900 GPS Lat 21-48.7' N
    09 40-25 55 20.1 GPS Long 130-07.5E
    09 41-05 55 20.6
    09 41-37 55 21.6 Ht eye 107 ft
    09 42-08 55 21.8 IE  0.8 on
    09 42-45 55 22.3 all shots upper limb
    09 43-21 55 23.4
    09 44-38 55 24
    09 45-18 55 24.6
    09 45-58 55 24.8
    09 47-06 55 25.3
    09 47-38 55 25.2
    09 48-15 55 25.6
    09 48-51 55 27.5
    09 49-24 55 26.8
    09 50-00 55 27.5
    09 50-34 55 27.2 LAM
    09 51-19 55 27.2 LAM LAM by calc
    09 51-45 55 26.8
    09 52-28 55 26.9
    09 52-59 55 26.5
    09 53-48 55 26.8
    09 54-19 55 26.8
    09 54-52 55 26.1
    09 55-19 55 25.6
    09 55-53 55 24.8
    09 57-13 55 24.5
    09 57-50 55 25.1
    09 58-37 55 23.2
    09 59-23 55 22.8
    10 00-00 55 22.4
    10 00-58 55 23
    10 01-35 55 22.1
    Jeremy
     
     
    In a message dated 1/27/2011 4:36:29 A.M. Central Asia Standard Time, jn.wilson{at}juno.com writes:
    I discussed all this in my Navigation paper. It's at:
     
     
    at the bottom of page 10.
     
    The moon can be used, but my students who have tried it say, "Never again"! I've never attempted it.
     
    Jim Wilson
     
    On Tue, 25 Jan 2011 21:49:28 EST Anabasis75---.com writes:
    The idea is pretty basic.  You determine Longitude based on your measured time of LAN.  The trouble is that the when you or the sun are moving N/S while shooting all of the sights, the curve of the apparent altitude is displaced a bit giving you the wrong time of LAN, there therefore longitude.
     
    The method of Lat and Long at transit works best when you are stationary and the sun is near the solstice (changing declination very little).  The method works fairly well with the planets since their change of declination is usually small.  It would work well with stars if you actually observe them over a long twilight.  The moon is probably an exercise in futility without a computer as the declination changes fairly dramatically. 
     
    You can still use the method but corrections for the various bodies' change in declination and your motion are needed.
     
    Jeremy
     
    In a message dated 1/24/2011 10:07:24 P.M. Central Asia Standard Tim, goold{at}vwc.edu writes:
    Jim,
    That is not surprising, since I don't understand the effect of declination change on determination of longitude.  At this point, I am abstracting from as much change as I can.  I am trying to wrap my little brain around the problem of determining the longitude of my front garden.  The problem of establishing the longitude of a vessel in motion is too much at this point.   I would be happy to be instructed, however.  That is the change you are talking about, isn't it-- the observer in motion?

    Patrick

    On Mon, Jan 24, 2011 at 12:23 AM, James N Wilson <jn.wilson{at}juno.com> wrote:
    Patrick:

    You still haven't shown that you understand the effect of declination
    change on the determination of longitude. But you're with the majority.

    Jim Wilson
    ____________________________________________________________
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    757 455 3357

    Charles Olson: "Love the World -- and stay inside it."

     


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