vertical sextant angle

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The angle in the vertical plane between the top of (say) a moderately close lighthouse, or other prominent feature, and the sea level below it read on a sextant. If the height of the top of the observed object is known, the distance off the object can be found either by trigonometry or from a table included in most nautical almanacs and tables. Allowance for tidal heights must be made when necessary. Vertical sextant angles are particularly useful to the navigator who wants to keep a definite distance off a particular point, when the angle corresponding to the required distance can be pre-set on the sextant.

Subjects: Maritime History.

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