In astronomy, a circle of the sphere drawn through a solstitial point, parallel to the equator; or the line which bounds the sun’s declination from the equator, north or south. This declination is twenty-three degrees and a half nearly. There are two tropics; the tropic of Cancer, on the north of the equator, and the tropic of Capricorn on the south.

Tropics, in geography, are two lesser circles of the globe, drawn parallel to the equator through the beginning of Cancer and of Capricorn.