The Tropic of Cancer, or the Northern tropic, is one of five major degree measures or major circles of latitude that mark maps of the Earth. It is the northmost latitude at which the sun can appear directly overhead at noon. This event occurs at the June solstice, when the northern hemisphere is tilted towards the sun to its maximum extent.
Monument marking the Tropic of Cancer northeast of Villa de Cos, Zacatecas, Mexico.
The Tropic of Cancer currently lies 23° 26′ 22″ north of the Equator. North of this latitude are the subtropics and the North Temperate Zone. The equivalent line of latitude south of the Equator is called the Tropic of Capricorn, and the region between the two, centered on the Equator, is the tropics.
The position of the Tropic of Cancer is not fixed, but rather it varies in a complicated manner over time; see under circles of latitude for information.
Starting at the Prime Meridian and heading eastwards, the Tropic of Cancer passes through:
Road sign South of Dakhla, Western Sahara (claimed by Morocco) marking the Tropic of Cancer. The sign was placed by the Budapest-Bamako rally participants, thus the non-English inscription is in Hungarian.
The imaginary line is called the Tropic of Cancer because when it was named the sun was in the direction of the constellationCancer (Latin for crab) at the June solstice. However, this is no longer true due to the precession of the equinoxes. According to International Astronomical Union boundaries, the Sun now is in Taurus at the June solstice. According to sidereal astrology, which divides the zodiac into 12 equal parts, the Sun is in Gemini at that time. The word "tropic" itself comes from the Greek tropos, meaning turn, referring to the fact that the sun appears to "turn back" at the solstices.
Circumnavigation
According to the Fédération Aéronautique Internationale's rules, for a flight to compete for a round-the-world speed record, it must cover a distance no less than the length of the Tropic of Cancer, as well as cross all of the meridians, and end on the same airfield where it started. This length is set to be 36,787.559 kilometers - a number which implies a precision that certainly does not exist, considering the variations of the Tropic of Cancer as described above.
For an ordinary circumnavigation the rules are somewhat relaxed and the distance is set to a rounded value of at least 37,000 kilometers.
