The Tropic of Cancer, which is also referred to as the Northern Tropic, is the most northerly circle of

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

at which the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

can be directly overhead. This occurs on the

June solstice The June solstice is the solstice on Earth that occurs annually between 20 and 22 June according to the Gregorian calendar. In the Northern Hemisphere, the June solstice is the summer solstice (the day with the longest period of daylight), whi ...

, when the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

is tilted toward the Sun to its maximum extent. It also reaches 90 degrees below the horizon at solar midnight on the December Solstice. Using a continuously updated formula, the circle is currently north of the Equator. Its Southern Hemisphere counterpart, marking the most southerly position at which the Sun can be directly overhead, is the

Tropic of Capricorn The Tropic of Capricorn (or the Southern Tropic) is the circle of latitude that contains the subsolar point at the December (or southern) solstice. It is thus the southernmost latitude where the Sun can be seen directly overhead. It also reac ...

. These tropics are two of the five major circles of latitude that mark maps of Earth, the others being the

Arctic The Arctic ( or ) is a polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenland), Finland, Iceland, N ...

and Antarctic circles and the Equator. The positions of these two circles of latitude (relative to the Equator) are dictated by the tilt of Earth's axis of rotation relative to the plane of its orbit, and since the tilt changes, the location of these two circles also changes. In geopolitics, it is known for being the southern limitation on the mutual defence obligation of

NATO The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two No ...

, as member states of NATO are not obligated to come to the defence of territory south of the Tropic of Cancer.

Name

When this line of latitude was named in the last centuries

BCE Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the or ...

, the Sun was in the constellation

Cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

(

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for ''

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

'') at the

, the time each year that the Sun reaches its zenith at this latitude. Due to the

precession of the equinoxes In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In partic ...

, this is no longer the case; today the Sun is in

Gemini Gemini may refer to: Space * Gemini (constellation), one of the constellations of the zodiac ** Gemini in Chinese astronomy * Project Gemini, the second U.S. crewed spaceflight program * Gemini Observatory, consisting of telescopes in the Norther ...

at the June solstice. The word "tropic" itself comes from the Greek "trope (τροπή)", meaning turn (change of direction, or circumstances), inclination, referring to the fact that the Sun appears to "turn back" at the solstices.

Drift

The Tropic of Cancer's position is not fixed, but constantly changes because of a slight wobble in the Earth's longitudinal alignment relative to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agains ...

, the plane in which the Earth orbits around the Sun. Earth's axial tilt varies over a 41,000-year period from 22.1 to 24.5 degrees, and is about 23.4 degrees, which will continue to remain valid for about a

millennium A millennium (plural millennia or millenniums) is a period of one thousand years, sometimes called a kiloannum (ka), or kiloyear (ky). Normally, the word is used specifically for periods of a thousand years that begin at the starting point (ini ...

. This wobble means that the Tropic of Cancer is currently drifting southward at a rate of almost half an arcsecond (0.468″) of latitude, or , per year. The circle's position was at exactly 23° 27′N in 1917 and will be at 23° 26'N in 2045. The distance between the

Antarctic Circle The Antarctic Circle is the most southerly of the five major circles of latitude that mark maps of Earth. The region south of this circle is known as the Antarctic, and the zone immediately to the north is called the Southern Temperate Zone. So ...

and the Tropic of Cancer is essentially constant as they move in tandem. This is based on an assumption of a constant equator, but the precise location of the equator is not truly fixed. See: equator,

axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orb ...

and circles of latitude for additional details.

Geography

North of the tropic are the subtropics and the

North Temperate Zone In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

. The equivalent line of latitude south of the Equator is called the

, and the region between the two, centered on the Equator, is the

tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referr ...

. In the year 2000, more than half of the world's population lived north of the Tropic of Cancer. There are approximately 13 hours, 35 minutes of daylight during the summer solstice. During the winter solstice, there are 10 hours, 41 minutes of daylight. Using 23°26'N for the Tropic of Cancer, the tropic passes through the following countries and territories starting at the

prime meridian A prime meridian is an arbitrary meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great ...

and heading eastward:

Climate

The climate at the Tropic of Cancer is generally hot and dry, except for cooler highland regions in China, marine environments such as Hawaii, and easterly coastal areas, where

orographic rainfall In meteorology, the different types of precipitation often include the character, formation, or phase of the precipitation which is falling to ground level. There are three distinct ways that precipitation can occur. Convective precipitation is g ...

can be very heavy, in some places reaching annually. Most regions on the Tropic of Cancer experience two distinct seasons: an extremely hot summer with temperatures often reaching and a warm winter with maxima around . Much land on or near the Tropic of Cancer is part of the

Sahara Desert , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...

, while to the east, the climate is torrid

monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...

al 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

Yu Shan Yu Shan or Yushan, also known as Mount Jade, Jade Mountain, or , and known as Mount Niitaka during Japanese rule, is the highest mountain in Taiwan at above sea level, giving Taiwan the 4th-highest maximum elevation of any island in the ...

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...

; though it had glaciers descending as low as during the Last Glacial Maximum, none survive and at present no glaciers exist within of the Tropic of Cancer; the nearest currently surviving are the Minyong and Baishui in the

Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...

to the north and on

Iztaccíhuatl Iztaccíhuatl (alternative spellings include Ixtaccíhuatl, or either variant spelled without the accent) ( or, as spelled with the x, ), is a dormant volcanic mountain in Mexico located on the border between the State of Mexico and Puebla withi ...

to the south.

Circumnavigation

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. Length of the Tropic of Cancer is :Bakker et al., Radio Positioning at Sea: Geodetic Survey Computations Least Squares Adjustment, 1995 (ISBN:90-6275-537-2)

l=2\pi \cos(\varphi) 6378137 (1-0.00669438(\sin(\varphi))^2)^

For an ordinary

circumnavigation Circumnavigation is the complete navigation around an entire island, continent, or astronomical body (e.g. a planet or moon). This article focuses on the circumnavigation of Earth. The first recorded circumnavigation of the Earth was the Mage ...

the rules are somewhat relaxed and the distance is set to a rounded value of at least .

Gallery

File:Tropicofcancer.jpg, Road sign south of Dakhla,

Western Sahara Western Sahara ( '; ; ) is a disputed territory on the northwest coast and in the Maghreb region of North and West Africa. About 20% of the territory is controlled by the self-proclaimed Sahrawi Arab Democratic Republic (SADR), while the ...

marking the Tropic of Cancer. The sign was placed by

Budapest-Bamako The Budapest-Bamako or Great African Run is a charity car race in Africa, and the largest amateur rally in the world. It is a low-budget version of the Dakar Rally, and goes from Budapest, Hungary to Bamako, Mali through t ...

rally participants; thus, the inscription is in English and Hungarian. File:TropicofCancer JC IMG 5135.jpg , Road Sign near Mehsana City in Gujarat State, India

Mehsana Mehsana (), also spelled Mahesana, is a city and municipality in Mehsana district, in the Indian state of Gujarat. Established in 14th century, the city was under Gaekwads of Baroda State from 18th century to the independence of India in 1947 ...

Gujarat Gujarat (, ) is a state along the western coast of India. Its coastline of about is the longest in the country, most of which lies on the Kathiawar peninsula. Gujarat is the fifth-largest Indian state by area, covering some ; and the ninth ...

File:Tropic of Cancer - a few miles from Rann of Kutch.jpg, Sign marking the Tropic of Cancer a few kilometres from

Rann of Kutch The Rann of Kutch (alternately spelled as Kuchchh) is a large area of salt marshes that span the border between India and Pakistan. It is located in Gujarat (primarily the Kutch district), India, and in Sindh, Pakistan. It is divided into ...

, India File:Tropic of cancer passes through Madhay Pradesh.jpg, Sign marking the Tropic of Cancer in

Madhya Pradesh Madhya Pradesh (, ; meaning 'central province') is a state in central India. Its capital is Bhopal, and the largest city is Indore, with Jabalpur, Ujjain, Gwalior, Sagar, and Rewa being the other major cities. Madhya Pradesh is the seco ...

, India File:Tropic of cancer nadia wb india.jpg, Sign marking the Tropic of Cancer on National Highway 34 in

Nadia District Nadia () is a district in the state of West Bengal, India. It borders Bangladesh to the east, North 24 Parganas and Hooghly districts to the south, Purba Bardhaman to the west, and Murshidabad to the north. Nadia district is highly influenti ...

West Bengal West Bengal (, Bengali: ''Poshchim Bongo'', , abbr. WB) is a state in the eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabitants within an area of . West Bengal is the fou ...

, India File:Ruisui Tropic of Cancer Marker 20100204.jpg, Ruisui Tropic of Cancer Marker in Ruisui Township,

Hualien County Hualien County ( Mandarin Wade–Giles: Hua¹-lien² Hsien⁴; Pīnyīn: ''Huālián Xiàn''; Hokkien POJ: ''Hoa-lian-koān'' or ''Hoa-liân-koān''; Hakka PFS: ''Fâ-lièn-yen''; Amis: ''Kalingko'') is a county on the east coast of Taiwan. I ...

References

External links

Temporal Epoch Calculations
See: Obliquity of the ecliptic {{geographical coordinates , state = collapsed N23 Tropics