Zē'nith, n.
(Synop., § 130), n. [Fr. zénith, Sp. zenit, cenit, Pg. zenit, zenith, It. zenit, abbreviated from Ar. semt-ur-râs, way of the head, vertical place, from semt, way, path, al, ul, the, and râs, head.] 1. That point in the visible celestial hemisphere which is vertical to the spectator; the point of the heavens directly overhead;—opposed to nadir.
From morn To noon he fell, from noon to dewy eve, A summer’s day; and with the setting sun Dropped from the zenith like a falling star. Milton.
Sense 2. Hence, figuratively, the point of culmination; greatest height; hence, the height of success or prosperity.
I find my zenith doth depend upon A most auspicious star. Shak.
It was during those civil troubles . . . this aspiring family reached the zenith. Macaulay.
Zenith distance (Astron.), the distance of the sun or a star from the zenith; the complement of the altitude.—Zenith sector, an instrument for measuring with great accuracy the distances from the zenith of stars which pass near that point.—Zenith telescope (Geodesy), a telescope specially designed for determining the latitude by means of any two stars which pass the meridian about the same time, and at nearly equal distances from the zenith, but on opposite sides of it. It turns both on a vertical and an horizontal axis, is provided with a graduated vertical semicircle, and a level for setting it to a given zenith distance, and with a micrometer for measuring the difference of the zenith distances of the two stars.