Nadir

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For other uses, see Nadir (disambiguation).

The nadir (from Arabic nazir, "opposite") is the astronomical term for the point in the sky directly below the observer, or more precisely, the point in the sky with an inclination of -90°.

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.

By association, nadir is also used to mean the lowest point, or time of greatest adversity. In economics, nadir means a low in the price of products. In medicine, nadir can also be used to refer to the lowest blood count for a given patient in a given period of time (i.e., a patient's nadir ANC or absolute neutrophil count).

Nadir also refers to a downward-facing viewing angle of an orbiting satellite, such as is employed during remote sensing of the atmosphere.