Meridian

(me-rid'e-an.) [L. meri dies, mid-day.] (Ast.) A great circle of the celestial sphere which pa es through both poles of the heavens, and also through the zenith and nadir of any place on the earth's surface. Every place on the earth's surface has consequently its own M. The M. is divided by the polar axis into two equal portions, which stretch from pole to pole, one on each side of the earth. It is mid-day at any place on the earth's surface when the centre of the sun comes upon the M. of that place; at the same instant it is mid-day at all places under the same half of that M., and midnight at all places under the opposite half. All places under the same M. have, therefore, the same longitude. See LONGITUDE. [s. 593]