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    Ex-meridian Time Sight Fix & Air/Space
    From: Bruce J. Pennino
    Date: 2013 Nov 12, 19:18 -0500
    
    Hello:
     
    I was going to do the same type of analysis, but I seem to remember that the greatest accurcacy occurs with the time sight done a few hours (at least)  before or after noon. FER wrote this not to long ago?  I was going to use some earlier recorded sight data, but  never got to it.  Data with HS 15-20 degrees. Given the variation in sine and cosine functions it makes sense that accuracy is probably quite good (not very sensitive relatively) with the sun low in the sky. I believe it was standard practice to do early morning and  early evening sights, in the 1850s - early 1900s?  I think I read this in Mixter 's Primer of Navigation??
     
    This past weekend we were in DC and went to Air/Space.  I spent 1 1/2 hours in "Time and Navigation".  I could have spent another hour. It is excellent and gives great credit to Weems.  Just down the hall is an excellent exhibit on "The Wright Brothers"; I also briefly listened to an "Old Timer" ...kinda like me....discussing the Wrights, lift/drag, etc. Also excellent! I never reached the exhibit "Pioneers of Flight".......I must get back there when time is less pressing.  I recomend  it all, very  highly.
     
    Best regards,

    Bruce
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
    ----- Original Message -----
    Sent: Tuesday, November 12, 2013 5:24 PM
    Subject: [NavList] Ex-meridian Time Sight Fix


    I thought it would be interesting to explore the ex-meridian/time sight fix obtained from a single observation (similar to the timed LAN and ex-meridian/LOP). It turns out that the time sight observed near LAN is very sensitive to the assumed latitude.. Attached is a plot that shows two time sights. The first using the GPS latitude and the second using the ex-meridian latitude. A 0.6' difference in the assumed latitude results in a 3' shift in longitude.

    Greg Rudzinski
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