Noun

(en noun)

(astronomy) The point, in an orbit about the Earth, that is closest to the Earth: the periapsis of an Earth orbiter.

* '>citation

(astronomy, more generally) The point, in an orbit about any planet, that is closest to the planet: the periapsis of any satellite.

* 1995 , John H. Rogers, The Giant Planet Jupiter , Cambridge University Press, ISBN 978-0-521-41008-3, page 335:

Conjunctions of I and II [Io and Europa] occur when they are near perigee' and apogee respectively; conjunctions of II and III [Europa and Ganymede] occur when II [Europa] is near ' perigee .

* 2002 , Serge Brunier, Solar System Voyage , Cambridge University Press, ISBN 978-0-521-80724-1, page 36:

The resolution of the images obtained by this American probe [Messenger] will depend on its altitude [above Mercury] at any one time: about ten meters at perigee (200km altitude), but only one 1 km at apogee (15000km).

* 2010 , Ruth Walker and Mary M. Shaffrey et al., Exploring Space: The High Frontier , Jones & Bartlett Learning, ISBN 978-0-7637-8961-9, page 129:

[Nereid’s] apogee—farthest point from Neptune—is five times the distance of its perigee —its closest point.

(possibly, archaic, outside, astrology) The point, in any trajectory of an object in space, where it is closest to the Earth.

Noun

(en noun)

(astronomy) The point in the sky vertically above a given position or observer; the point in the celestial sphere opposite the nadir.

* 1638 Herbert, Sir Thomas Some years travels into divers parts of Asia and Afrique

The 12 day wee had the wind high and large ?o that in two dayes ?aile we made the Sunne our Zenith or verticall point...

* 1671–1693 : Rev. Thomas Jolly, private notebook ; printed in:

* 1895 , Henry Fishwick (editor), The Note Book of the Rev. Thomas Jolly: A.D. 1671–1693. Extracts from the Church Books of Altham and Wymondhouses, 1649–1725. And an Account of the Jolly Family of Standish, Gorton, and Altham , page 44

In this 10th m. appeared that prodigious Comett the tayl whereof was like the blade of a double edged sword, and reached almost from the horizon to the zenith .

(astronomy) The highest point in the sky reached by a celestial body.

* 1719-

...in the middle of the day, when the sun was in the zenith , the violence of the heat was too great to stir out...

* 1920 , , The Understanding Heart , Chapter II:

As far to the west as Monica could see, her world was a sea of fog, , the fog gradually took on a bluish tinge.

Highest point or state; peak.

* Shakespeare

I find my zenith doth depend upon / A most auspicious star.

* Macaulay

It was during those civil troubles this aspiring family reached the zenith .

* {{quote-book

, page=173 , year=1900 , author=William Beckford , title=The History of the Caliph Vathek citation , passage="There for a while I enjoyed myself in the zenith of glory and pleasure."}}