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It should perhaps be remembered that when ex-meridians came into use from
the mid-nineteenth century on, very little graphical chartwork was used.
Latitude by mer-alt (or ex-meridian) and Longitude by long-chron were
worked up by traverse tables to give the noon position.

Regarding sights when the sun is near the zenith, zenith fixes are a handy
way of getting a fix. Admittedly I have only done a couple, one in the
Pacific near the Line islands and the other in the Indian Ocean (both from
aircratf). The trick is to get three sights with the azimuths about 60deg
apart, plot the sub solar point for each sight (GHA and dec) and using the
corrected ZD of each as radii plot three arcs of position; transfer the
p/l's for course and distance run and Bob's your uncle. The real problem is
the glare and making sure the sextant is vertical.


NG

   

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