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    A One-Hour Presentation on Celestial Navigation
    From: Geoffrey Kolbe
    Date: 2016 Mar 19, 08:50 +0000
    Happenstancially, I have been asked by my neighbours to give a talk to them about celestial navigation on the 4th of April, or some date near then when the sun is out - which is a rarity in this part of the world! It will about six people including grandchildren (youngest about 8) parents and grandparents (the males, not the females!)

    I have a 30" blow-up globe and a large pair of compasses, which I intend to be the centrepiece of my demonstration.

    I was thinking to start proceeding with everyone taking an altitude of the sun with a variety of sextants/aircraft-octants that I have. They won't know what they are doing, but it gives an introduction to the instruments of navigation.

    This will be followed by a talk on the notion that the sun is always directly above some point on the earth, and at that point the sun casts no shadow. There are circles around this point where the shadow will have the same length - that is, the sun is the same distance above the horizon.

    Taking the altitudes measured by everybody at the start, and the place where we knew the sun was directly overhead at the time (its geographical position) I will then set the compasses to the co-angle of those altitudes and placing one point (a sucker, actually) on the GP I will draw a line through this part of the globe, which should go neatly through the Borders of Scotland, where we will be.

    That is the essence of celestial navigation. Then, some discussion about chronometers, tables, assumed positions, by which time an hour or so will have passed and we can all take another sighting with the sextants/octants. 

    The line drawn from this second sighting should cross that of the first sighting close to where we are on the globe - we will have a celestial fix.

    Anybody have any experience with 8 year olds using sextants...?

    Geoffrey Kolbe
       
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