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nadir(nā`dər) [Arab.,=opposite], in astronomy, the point on the celestial spherecelestial sphere,
imaginary sphere of infinite radius with the earth at its center. It is used for describing the positions and motions of stars and other objects. For these purposes, any astronomical object can be thought of as being located at the point where the line of sight
..... Click the link for more information. directly opposite the zenithzenith,
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.
..... Click the link for more information. , i.e., directly beneath the observer.
nadir(nay -deer) The point on the celestial sphere that lies directly beneath an observer and is therefore unobservable. It is diametrically opposite the observer's zenith and with the zenith lies on the observer's meridian.
Nadir(religion, spiritualism, and occult)
The nadir is the point in the heavens directly opposite the zenith, which means that it is the point in the heavens on the other side of Earth directly underneath one’s feet. It should be carefully distinguished from the imum coeli, which is the point directly opposite the midheaven.