ALTITUDE, PARALLAX OF, is an arch of a vertical circle, by which the true altitude, observed at the centre of the earth, exceeds that which is observed on the surface. See PARALLAX (Encycl.) and ASTRONOMY (Suppl.) ALTITUDE of the Nonagesimal, is the altitude of the 90th degree of the ecliptic, counted upon it from where it cuts the horizon, or of the middle or highest point of it which is above the horizon, at any time; and is equal to the angle made by the ecliptic and horizon where they intersect at that time. ALTITUDE ALTITUDE of the Cone of the Earth's or Moon's Shadow, the height of the shadow of the body made by the sun, and measured from the centre of the body. To find it say, As the tangent of the angle of the sun's apparent semidiameter is to radius; so is 1 to a fourth proportional, which will be the height of the shadow in semidiameters of the body.