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    Re: Zenith Fixes
    From: David Pike
    Date: 2019 Mar 23, 15:54 -0700

    Tony Re your 23rd 17.33UTC post, 
    12kts is 1nm in 60/12=5min or 1/5nm/minute.  Therefore in 9 min you’d travel 1.8nm.  It’s a bit difficult to move an arc, so just move the sub stellar point 1.8nm on 164 degrees before you draw the first arc instead.  Similarly, to get the DR position at 12.00 just move the 11.21 fix 39x1/5 = 7.8nm along 164 degrees.  Tide and leeway aren’t given, so ignore.

    I’m afraid we both live too far north to try this on the Sun, but if you lived in tropical regions it ought to be possible occasionally.  We could try standing under a street lamp and bringing it down to the end of the road.  Bubble sextants aren’t much use on a yacht; it’s too bumpy.  I do occasionally look to see if I could use a star; a bubble sextant would be good on land, because you wouldn’t be restricted to twilight.  So far I’ve not managed it.  You would need a star whose sub point passes within about 120nm (Hc = 88) of you, a clear sky, and the time to do it.  According to ‘Navigator’, there’s nothing passing within about 300nm of me at night at the moment.  DaveP

       
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