nadir

nadir [Arab.,=opposite], in astronomy, the point on the celestial sphere directly opposite the zenith, i.e., directly beneath the observer.

(born Oct. 22, 1688, Kobhan, Ssubdotafavid Iran—died June 1747, near Fathsubdotābād) Iranian conqueror and ruler. Originally a bandit of the Turkish Afshar tribes, he helped restore Tsubdotahmāsp II of the Ssubdotafavid dynasty to Iran's throne, defeating the Ghilzay Afghan usurper Mahsubdotmūd. He later deposed Tsubdotahmāsp II to place the latter's infant son on the throne; he made himself regent, then deposed the son and took the throne himself in 1736. He engaged in constant warfare with his neighbours, enlarging his empire from the Indus River to the Caucasus Mountains. Suspicious of those around him and capriciously cruel, he was assassinated by his own troops.

Learn more about Nādir Shāh with a free trial on Britannica.com.

The nadir (from Arabic ندير nadeer نظير nathir, "opposite") is the astronomical term for the point directly below the observer, or more precisely, the point with an inclination of −90°. In simple terms, if you are standing on the Earth, it is the direction "down" toward your feet.

Geometrically, it is the point on the celestial sphere intersected by a line drawn from the observer's location on the Earth's surface through the center of the Earth. The point opposite the nadir is the zenith. Nadir also refers to a downward-facing viewing angle of an orbiting satellite, such as is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing an EVA.

The word is also used figuratively to mean the lowest point of a person's spirits.

See Also

• Zenith

References