Tropic of Cancer is an imaginary line that traces the northern boundary of the earth's Tropical Zone. It marks the farthest limit north of the equator where the sun can appear directly overhead. The line lies 23 degrees 27 minutes north of the equator. The vertical rays of the sun shine down on the Tropic of Cancer at noon on the day of the summer solstice, which is June 20, 21, or 22.