## zenith

zenith, in astronomy, the point in the sky directly overhead; more precisely, it is the point at which the celestial sphere is intersected by an upward extension of a plumb line from the observer's location. Its position in the sky thus depends on the direction of the earth's gravitational field at the observer's location. The zenith is a reference point in the altazimuth coordinate system; its altitude above the celestial horizon is 90°. The angular distance from the zenith to a celestial body is called the zenith distance. The nadir, directly opposite the zenith, has a zenith distance of 180°; the celestial horizon has a zenith distance of 90°.

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"zenith." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 28 May. 2017 <http://www.encyclopedia.com>.

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## zenith

ze·nith / ˈzēni[unvoicedth]/ • n. [in sing.] the highest point reached by a celestial or other object: the missile reached its zenith and fell. ∎  the point in the sky or celestial sphere directly above an observer.The opposite of nadir. ∎  the time at which something is most powerful or successful: under Justinian, the Byzantine Empire reached its zenith of influence. DERIVATIVES: ze·nith·al / -nə[unvoicedth]əl/ adj.

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"zenith." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 28 May. 2017 <http://www.encyclopedia.com>.

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"zenith." The Oxford Pocket Dictionary of Current English. . Retrieved May 28, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/zenith-2

## zenith

zenith the highest point reached by a celestial or other object; the point in the sky or celestial sphere directly above an observer; in figurative usage, the time at which something is most powerful or successful. Recorded from late Middle English, the word comes via Old French from medieval Latin cenit, based on Arabic samt (ar-ra's) ‘path (over the head)’.

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## zenith

zenith point of the sky directly overhead, †point of the horizon at which a heavenly body rises XIV; highest point or state XVII. ME. cenyth, senith, cinit — OF. cenit (mod. zénith) or medL. cenit, obscurely — Arab. samt in samt ar-ra's ‘path over the head’ (samt way, al the, AL-2, ra's head).

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"zenith." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 28 May. 2017 <http://www.encyclopedia.com>.

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## zenith

zenith In astronomy, point on the celestial sphere that is directly overhead. The zenith distance of a heavenly body is the angle it makes with the zenith. It is diametrically opposite the nadir.

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"zenith." World Encyclopedia. . Encyclopedia.com. 28 May. 2017 <http://www.encyclopedia.com>.

"zenith." World Encyclopedia. . Encyclopedia.com. (May 28, 2017). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/zenith

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## zenith

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"zenith." Oxford Dictionary of Rhymes. . Encyclopedia.com. 28 May. 2017 <http://www.encyclopedia.com>.

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## ZENITH

ZENITH (ˈzɛnɪɵ) Nuclear engineering zero-energy nitrogen-heated thermal reactor