|zenith (ˈzɛnɪθ, US ˈziːnɪθ)|
|1.||astronomy the point on the celestial sphere vertically above an observer|
|2.||the highest point; peak; acme: the zenith of someone's achievements|
|[C17: from French cenith, from Medieval Latin, from Old Spanish zenit, based on Arabic samt, as in samt arrās path over one's head, from samt way, path + al the + rās head]|
point on the celestial sphere directly above an observer on the Earth. The point 180 opposite the zenith, directly underfoot, is the nadir. Astronomical zenith is defined by gravity; i.e., by sighting up a plumb line. If the line were not deflected by such local irregularities in the Earth's mass as mountains, it would point to the geographic zenith. Because the Earth rotates and is not a perfect sphere, the geocentric zenith is slightly different from the geographic zenith except at the Equator and the poles. Geocentric zenith is the intersection with the celestial sphere of a straight line drawn through the observer's position from the geometric centre of the Earth
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