From the ancient Greek verb, "trépomai", return, are the two parallels of the celestial sphere, located at 23 ° 27 'of latitude N and 23 ° 26' of latitude S. They are the two points located further north and south , respectively, of the terrestrial surface where the sun's rays perpendicularly affect the Earth, at noon, at least one day a year, the day of the summer Solstice (June 22) and the day of the winter solstice (December 22 ).
The tropic located north of the equator is called the Tropic of Cancer, because the Sun, in the summer solstice (at that time, for the northern hemisphere, in which the sun's rays fall perpendicularly over the tropics), enters the constellation of Cancer. The tropics located south of the equator, for a similar reason, is called the Tropic of Capricorn. This area of the earth's surface is known as tropical, intertropical or torrid zone.
The tropical adjective is also used to describe climatic conditions, vegetation, etc. similar to those in this geographical area.
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