Tropic of Cancer

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Coordinates: 23°26′16″N 0°0′0″W / 23.43778°N -0.00000°E / 23.43778; -0.00000 (Prime Meridian)

World map showing the Tropic of Cancer

The Tropic of Cancer, also referred to as the Northern tropic, is the circle of latitude on the Earth that marks the most northerly position at which the Sun may appear directly overhead at its zenith. This event occurs once per year, at the time of the June solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent. As of 2014, it lies at 23° 26' 14.675″ (23° 26′ 16″) north of the Equator.[1]

Its Southern Hemisphere counterpart, marking the most southerly position at which the Sun may appear directly overhead, is the Tropic of Capricorn. These tropics are two of the five major degree measures or major circles of latitude that mark maps of the Earth, besides the Arctic and Antarctic Circles and the Equator. The positions of these circles of latitude (other than the Equator) are dictated by the tilt of the Earth's axis of rotation relative to the plane of its orbit.

Name[edit]

Road sign South of Dakhla, Western Sahara marking the Tropic of Cancer. The sign was placed by the Budapest-Bamako rally participants, thus the non-English inscription is in Hungarian.
Tropic of Cancer passes through National Highway 34 in Nadia District, West Bengal, India

The imaginary line is called the Tropic of Cancer because when the Sun reaches the zenith at this latitude, it is entering the tropical sign of Cancer (summer solstice in the northern hemisphere). When it was named, the Sun was also in the direction of the constellation Cancer (Latin for crab). 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. However, according to tropical astrology, which divides the ecliptic in twelve 30° sectors, starting with the vernal equinox, the Sun is always entering Cancer at this time, as the Earth's axial tilt is most inclined towards the Sun. 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.

Tropic of cancer passes through Madhya Pradesh

Geography[edit]

Carretera 83 (Vía Corta) Zaragoza-Victoria, km 27+800. Of all crossings of the Tropic of Cancer with Mexican federal highways, this is the only place where the latitude is marked with precision and where the annual drift between 2005 and 2010 can be appreciated.

The Tropic of Cancer position is not fixed, but varies in a complicated manner over time.[2] It drifts south almost half a second (0.47″) of latitude per year (it was at exactly 23° 27′ in year 1917).[3] See circles of latitude for further information.

North of Tropic of Cancer 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.

Starting at the Prime Meridian and heading eastward, the Tropic of Cancer passes through:

Co-ordinates Country, territory or sea Notes
23°26′N 0°0′E / 23.433°N 0.000°E / 23.433; 0.000 (Prime Meridian)  Algeria
23°26′N 11°51′E / 23.433°N 11.850°E / 23.433; 11.850 (Niger)  Niger
23°26′N 12°17′E / 23.433°N 12.283°E / 23.433; 12.283 (Libya)  Libya The Tropic touches on the northernmost point of  Chad at 23°26′N 15°59′E / 23.433°N 15.983°E / 23.433; 15.983 (Northernmost point of Chad)
23°26′N 25°0′E / 23.433°N 25.000°E / 23.433; 25.000 (Egypt)  Egypt The Tropic passes through Lake Nasser
23°26′N 35°30′E / 23.433°N 35.500°E / 23.433; 35.500 (Red Sea) Red Sea
23°26′N 38°38′E / 23.433°N 38.633°E / 23.433; 38.633 (Saudi Arabia)  Saudi Arabia
23°26′N 52°8′E / 23.433°N 52.133°E / 23.433; 52.133 (United Arab Emirates)  United Arab Emirates Abu Dhabi emirate only
23°26′N 55°24′E / 23.433°N 55.400°E / 23.433; 55.400 (Oman)  Oman
23°26′N 58°46′E / 23.433°N 58.767°E / 23.433; 58.767 (Indian Ocean) Indian Ocean Arabian Sea
23°26′N 68°23′E / 23.433°N 68.383°E / 23.433; 68.383 (India)  India States of Gujarat, Rajasthan, Madhya Pradesh, Chhatisgarh, Jharkhand and West Bengal
23°26′N 88°47′E / 23.433°N 88.783°E / 23.433; 88.783 (Bangladesh)  Bangladesh Khulna, Dhaka, and Chittagong Divisions
23°26′N 91°14′E / 23.433°N 91.233°E / 23.433; 91.233 (India)  India State of Tripura
23°26′N 91°56′E / 23.433°N 91.933°E / 23.433; 91.933 (Bangladesh)  Bangladesh Chittagong Division
23°26′N 92°19′E / 23.433°N 92.317°E / 23.433; 92.317 (India)  India State of Mizoram
23°26′N 93°23′E / 23.433°N 93.383°E / 23.433; 93.383 (Myanmar)  Burma (Burma) Chin State, Sagaing Division, Mandalay Division, Shan State
23°26′N 98°54′E / 23.433°N 98.900°E / 23.433; 98.900 (China)  China Provinces of Yunnan (passing about 7 km north of the border with  Vietnam), Guangxi, and Guangdong
23°26′N 117°8′E / 23.433°N 117.133°E / 23.433; 117.133 (Taiwan Strait) Taiwan Strait
23°26′N 120°8′E / 23.433°N 120.133°E / 23.433; 120.133 (Taiwan)  Republic of China (Taiwan) Chiayi County, Hualien County
23°26′N 121°29′E / 23.433°N 121.483°E / 23.433; 121.483 (Pacific Ocean) Pacific Ocean Passing just south of Necker Island, Hawaii,  United States
23°26′N 110°15′W / 23.433°N 110.250°W / 23.433; -110.250 (Mexico)  Mexico State of Baja California Sur
23°26′N 109°24′W / 23.433°N 109.400°W / 23.433; -109.400 (Gulf of California) Gulf of California
23°26′N 106°35′W / 23.433°N 106.583°W / 23.433; -106.583 (Mexico)  Mexico States of Sinaloa, Durango, Zacatecas, San Luis Potosí, Nuevo León, and Tamaulipas
23°26′N 97°45′W / 23.433°N 97.750°W / 23.433; -97.750 (Gulf of Mexico) Gulf of Mexico
23°26′N 83°0′W / 23.433°N 83.000°W / 23.433; -83.000 (Atlantic Ocean) Atlantic Ocean Passing through the Straits of Florida and the Nicholas Channel
Passing just south of the Anguilla Cays ( Bahamas)
Passing through the Santaren Channel and into the open ocean
23°26′N 76°0′W / 23.433°N 76.000°W / 23.433; -76.000 (Bahamas)  Bahamas Exuma Islands and Long Island
23°26′N 75°10′W / 23.433°N 75.167°W / 23.433; -75.167 (Atlantic Ocean) Atlantic Ocean
23°26′N 15°57′W / 23.433°N 15.950°W / 23.433; -15.950 (Western Sahara) Western Sahara Claimed by  Morocco and the  Sahrawi Arab Democratic Republic
23°26′N 12°0′W / 23.433°N 12.000°W / 23.433; -12.000 (Mauritania)  Mauritania
23°26′N 6°23′W / 23.433°N 6.383°W / 23.433; -6.383 (Mali)  Mali
23°26′N 2°23′W / 23.433°N 2.383°W / 23.433; -2.383 (Algeria)  Algeria

Climate[edit]

Excluding cooler highland regions in China, the climate at the Tropic of Cancer is generally hot and dry except for easterly coastal areas where orographic rainfall can be very heavy, in some places reaching 4 metres (160 in). Most regions on the Tropic of Cancer experience two distinct season: an extremely hot summer with temperatures often reaching 45 °C (113 °F) and a warm winter with maxima around 22 °C (72 °F). Most land on or near the Tropic of Cancer is part of the Sahara Desert, whilst to the east the climate is torrid monsoonal with a short wet season from June to September and very little rainfall for the rest of the year.

The highest mountain on or adjacent to the Tropic of Cancer is Yushan in Taiwan; though it had glaciers descending as low as 2,800 metres (9,190 ft) during the Last Glacial Maximum, none survive and at present no glaciers exist within 470 kilometres (290 mi) of the tropic of Cancer; the nearest currently surviving are the Minyong and Baishui in the Himalayas to the north and on Iztaccíhuatl to the south.

Circumnavigation[edit]

According to the rules of the Fédération Aéronautique Internationale, 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, cross all meridians, and end on the same airfield where it started.

To calculate the length of the Tropic:

  • At present, the radius of the circle is 6378 km x cos(23° 26′ 16″) which results in 5851.77 km
  • Then  \ell = \pi \cdot 2r = 3.1416 x 2 x 5851.77 which amounts to 36 768.
  • Therefore, assuming the Earth to be a perfect sphere, the length of the circumference at the parallel of the Tropics would be 36 768 km

For an ordinary circumnavigation the rules are somewhat relaxed and the distance is set to a rounded value of at least 37 000 kilometers.

External links[edit]

See also[edit]

References[edit]