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    Solar Back Sight with Davis Mk. 15 Sextant
    From: Richard B. Langley
    Date: 2015 Aug 28, 09:35 -0700

    As usual when I go on holiday to a place near the water, I take along a plastic sextant for fun and amusement. That's what I did on the present trip to Grassy Key in the Florida Keys. The house we're renting is right on The Gulf. Yesterday, I took some sun shots around noon a few metres from the shore. Since the back of the house faces north, I had to take back sights. I took three within an hour or so of local noon. I didn't take any of the special precautions one should when using a plastic sextant except for letting it come to ambient temperature when taking it from the air-conditioned house and letting the condensation on the mirrors evaporate. Once I realized that a lower-limb reduction becomes an upper-limb one for a back sight, I got a resonable position fix. Could be better, of course, but I don't get a chance to practice much. Being a bit lazy (I am on holiday), I used the Celestial iPhone app from Navimatics. The plot of the results and position fix is attached. My assumed position was obtained using a GPS receiver (N 24° 45.5', W 80° 58.2'), and the celestial fix was N 24° 49.5', W 81° 3.6'.

    -- Richard Langley 


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