, that point of the heavens diametrically under our feet, or opposite to the zenith, which is directly over our heads. The zenith and Nadir are the two poles of the horizon, each being 90° distant from it.
The Sun's Nadir, is the axis of the cone projected by the shadow of the earth: so called, because that axis being prolonged, gives a point in the ecliptic diametrically opposite to the sun.
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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.
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