Tropic

tropic

1. either of the parallel lines of latitude at about 23½°N (tropic of Cancer) and 23½°S (tropic of Capricorn) of the equator

2. the tropics that part of the earth's surface between the tropics of Cancer and Capricorn; the Torrid Zone

3. Astronomy either of the two parallel circles on the celestial sphere having the same latitudes and names as the corresponding lines on the earth

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Tropic 

one of two imaginary parallel circles on the surface of the globe, located 23°27’ north and south of the equator. The tropic of Cancer is north of the equator, and the tropic of Capricorn is south of the equator.

On the day of the summer solstice the sun passes through the northernmost point of its apparent path across the sky and is seen at the zenith at noon along the tropic of Cancer. This day has the longest period of daylight in the year in the northern hemisphere and the longest period of darkness in the southern hemisphere. At noon on the day of the winter solstice the sun is seen at the zenith along the tropic of Capricorn; this day has the shortest period of daylight in the year in the northern hemisphere and the longest period of daylight in the southern hemisphere. In the region between the tropics the sun is at the zenith twice a year at every point.