Tropics

Tropics (Gr., 'turning-points' or 'limits') are two parallels of latitude on the terrestrial globe, passing through the most northerly and southerly points on the earth's surface at which the sun is vertical. On the Armillary Sphere (q.v.), consequently, the ecliptic (the representation of the sun's path) touches but does not cross the tropics. The tropics include between them all those points on the earth's surface at which the sun is ever vertical. The tropic north of the equator is called the Tropic of Cancer, because the sun at the summer solstice (at which time he is vertically over that tropic) enters the constellation of Cancer; and the southern one is, for a similar reason, denominated the Tropic of Capricorn. Though usually said to be in 23½° N. and S. lat., the tropics are not absolutely fixed at a uniform distance from the equator, but the limits of their variation are extremely narrow (see ECLIPTIC). For 1st January 1882 the Nautical Almanac gave their position in 23° 27' 16" .60 N. and S. respectively; and for 1st January 1892, 23° 27' 11" .84 N. and S. The term subtropical is used somewhat loosely for a climate between tropical and temperate, and for the regions bordering on the tropics.