the angular distance from the zenith of a point on the celestial sphere to the sphere, measured along a great circle that is perpendicular to the horizon; the complement of the altitude.
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Origin of zenith distance
First recorded in 1695–1705
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for zenith distance
The zenith-distance of an object is the angle which the ray of light from it makes with the vertical direction thus defined.