Greetings, fellow dialists,
For astronavigators (are there any surviving?), when the sun is
virtually overhead it is possible to find your position without doing
any calculations. You measure the sun's altitude assuming it is within a
few minutes of arc from overhead, plot the sun's geographical position
on a map or chart, find the sun's zenith distance (90 deg - altitude)
and using this draw a small circle in miles (where one mile equals one
minute of arc) round the sun's location. This is your position circle
and you are somewhere on it. Wait a few minutes and repeat. This gives
another position circle west of the first. At one of the two
intersections of the circles is your true position (be careful to chose
the right one!)
Interestingly, it is also possible to do this with the planet Venus in
broad daylight. Having found Venus by first calculating her approximate
altitude you can afterwards, knowing pretty well where she lies, view
her with the naked eye in full sunlight.
Frank 55N 1W
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