Zenith

Science / Weather / Zenith: The point which is elevated 90 degrees from all points on a given observer's astronomical horizon. The point on any given observer's celestial sphere that lies directly above him. The opposite of nadir.
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Other Words for Zenith

Zenith Adjective Synonyms: meridian, summit, acme, apex, vertex, apogee, high point, top, peak, pinnacle
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Nadir

Science / Astrology / Nadir: The point in the celestial sphere directly opposite the zenith; the point directly beneath an observer on Earth; the low point. MORE

Prime Vertical

Science / Astrology / Prime Vertical: The great circle that rises vertically from the east point of the horizon and passes through Earth's zenith and nadir. MORE