prime vertical

British  

noun

1. astronomy the great circle passing through the observer's zenith and meeting the horizon due east and west

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Example Sentences

Sun Sight In order to make this a valuable sight for longitude it should be taken when the sun is on or as near as possible to the prime vertical.

From Lectures in Navigation by Draper, Ernest Gallaudet

The transit instrument is also used in the prime vertical for the determination of latitudes.

From Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6 "Geodesy" to "Geometry" by Various

If your A.M. sight was taken when the sun was on or near the prime vertical, a change in latitude at noon will make no change in longitude.

From Lectures in Navigation by Draper, Ernest Gallaudet

The usual observations made by navigators at sea consist in a meridian observation of the sun for latitude, and a morning and possibly afternoon observation of the sun near the prime vertical for longitude.

From International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884. Protocols of the Proceedings by Various

The sun might be observed for this purpose during the summer months, at moments when calculation showed that he should be due east or west, or crossing what is technically the prime vertical.

From The Contemporary Review, Volume 36, September 1879 by Various