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    Re: My first Lunar
    From: Frank Reed
    Date: 2008 Jul 15, 22:03 -0400

    Jeremy, you wrote:
    "Well I found my first lunar, and it will be tricky.  Here's the data that I
    have.
    
    GMT Date is 26 January 1999.  GMT of the sight was about 2220.  Dip
    correction is -7.7' of arc.  The lunar was at evening twilight and a near
    limb observation between Jupiter and the Moon was taken.  The sextant LD is
    68deg 19.4'  IC is 0.0'.  An upper limb altitude of the moon was taken HS is
    66 deg 09.3'  The Hs of Jupiter is 45 deg 22.3.
    
    Here's the rub:  I have no idea where I was other then to say I was probably
    somewhere in the Eastern Caribbean.  Best guess is about 20 deg North
    Latitude and 70 degrees West Longitude."
    
    Having a good DR position is convenient but not necessary when it comes to
    clearing a lunar. Of course if you want to assess the accuracy of the sight,
    then you want the actual position and correct GMT as nearly as possible. You
    can figure out where you are, more or less, by trial and error from your
    sight data. Go to the calculator on my web site, set the GMT of the sight to
    22:19:30 and set your DR Lat to 14d 31'N and your DR Lon to 61d 38.1W. That
    nearly matches your sights, lunar and altitudes, too. So assuming your
    observations were good (and I would bet they were) you were probably about
    30 miles west of Martinique. Does that fit your recollection?
    
    Now as it happens, this is yet another one of this miraculous lunar sights
    where you can do the clearing without using any spherical trig. If we take
    the pre-cleared altitudes and distance (the altitudes of the objects'
    centers and the center-to-center lunar distance) and add them up, we get
    nearly 180 degrees. So adjust the Moon's altitude higher by about 24 minutes
    of arc and then work it AS IF they were exactly opposite each other in the
    sky.
    
     -FER
    
    
    
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