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High-Altitude Sights

Sextant sights of celestial bodies that are over some 80 high. These sights are special for two reasons. First, they are difficult to take because it is difficult to tell which way to point the sextant as you rock it, and second, once taken, they must be reduced by special methods.

A standard sight reduction will not yield an accurate line of position for high-altitude sights. It is important to remember this whenever you sail under the sun. At heights of 75 to 85 or so, you can still do a standard sight reduction, but you must interpolate for the azimuth angle as explained in the Workform Instructions, and then you should also adjust the slopes of the lines as explained in the instructions to the sight reduction tables.

Above 85, it will be necessary to plot the geographical position on the plotting sheet and then plot a circle of position around it with a radius equal to the zenith distance of the sight. The book Emergency Navigation explains these sights with examples. See Rocking the Sextant, Sextant Sights, Sight Reduction, Circle of Position, and Zenith Distance.


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