CANCER, in Astronomy, one of the twelve signs, represented on the globe in the form of a crab, and thus marked (♋) in books. It is the fourth constellation in the starry zodiac, and that from which one quadrant of the ecliptic takes its denomination. The reason generally assigned for its name as well as figure, is a supposed resemblance which the sun's motion in this sign bears to the crab-fish. As the latter walks backwards, so the former, in this part of his course, begins to go backwards, or recede from us; though the disposition of stars in this sign is by others supposed to have given the first hint to the representation of a crab.
Tropic of CANCER, in Astronomy, a lesser circle of the sphere parallel to the equator, and passing through the beginning of the sign Cancer.