The term 'Line Around the World' refers to the Equator and the TROPIC of Cancer and the TROPIC of Capricorn. The Equator is an imaginary line that circles the Earth halfway between the North and South Poles, and is 7, 000 miles long. The TROPIC of Cancer and the TROPIC of Capricorn are two other lines of latitude that mark the northernmost and southernmost points at which the Sun can be directly overhead. These lines are located 23.5 degrees north and south of the Equator, respectively.