Tropic of Cancer

When this line of latitude was named in the last centuries BCE, the Sun was in the constellation Cancer (Latin: Crab) at the June solstice (90° ecliptic longitude). Due to the precession of the equinoxes, this is no longer the case; today the Sun is in constellation Taurus at the June solstice. The word "tropic" itself comes from the Greek "trope (τροπή)", meaning turn (change of direction or circumstance), inclination, referring to the fact that the Sun appears to "turn back" at the solstices.

File:Trópico de Cáncer en México - Carretera 83 (Vía Corta) Zaragoza-Victoria, Km 27+800.jpg (Vía Corta) Zaragoza-Victoria, km 27+800. Of the Tropic of Cancer's intersections with Mexican federal highways, this is the only one where it is precisely marked and the drift from 2005 to 2010 can be seen.|thumb]]

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 plane in which the Earth orbits around the Sun. Earth's axial tilt varies over a 41,000-year period from about 22.1 to 24.5 degrees, and {{as of|2000|lc=yes}} is about 23.4 degrees, which will continue to remain valid for about a millennium. 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 {{cvt|15|m}}, per year. The circle's position was at exactly 23° 27′N in 1917 and will be at 23° 26'N in 2045.[http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm Montana State University: Milankovitch Cycles & Glaciation] {{webarchive |url=https://web.archive.org/web/20110806021244/http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm |date=August 6, 2011 }}

The distance between the Antarctic Circle 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 and circles of latitude for additional details.

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North of the tropic 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.

In the year 2000, more than half of the world's population lived north of the Tropic of Cancer.{{cite web |last1=Quigley |first1=Robert |title=The World's Population Mapped by Latitude and Longitude |url=https://www.themarysue.com/world-population-latitude-longitude/ |website=The Mary Sue |date=12 August 2010 |access-date=11 January 2021}}

On 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 17 countries (including two disputed territories) and 8 water bodies, starting at the prime meridian and heading eastward:

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 can be very heavy, in some places reaching {{convert|4|m|in|-1}} annually. Most regions on the Tropic of Cancer experience two distinct seasons: an extremely hot summer with temperatures often reaching {{convert|45|C|F}} and a warm winter with maxima around {{convert|22|C|F}}. Much land on or near the Tropic of Cancer is part of the Sahara Desert, while 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 Yu Shan in Taiwan. It had glaciers descending as low as {{convert|2800|m|ft|-1}} during the Last Glacial Maximum. At present glaciers still exist aroundwithin {{convert|470|km|mi|-1}} the Tropic. The nearest currently surviving are the Minyong and Baishui in the Himalayas to the north and on Pico de Orizaba in Mexico to the south.

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.

The length of the Tropic of Cancer is {{cvt|36,788|km}}:Bakker et al., Radio Positioning at Sea: Geodetic Survey Computations Least Squares Adjustment, 1995 ({{ISBN|90-6275-537-2}})

:$l=2\backslash pi\; \backslash cos(\backslash varphi)\; 6378137\; (1-0.00669438(\backslash sin(\backslash varphi))^2)^\{-0.5\}$

:where φ is the latitude of the Tropic of Cancer

For an ordinary circumnavigation the rules are somewhat relaxed and the distance is set to a rounded value of at least {{convert|36,770|km|mi}}.

File:Tropicofcancer.jpg|Road sign south of Dakhla, marking the Tropic of Cancer. The sign was placed by Budapest-Bamako 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, Gujarat

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, Gujarat, India

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

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

File:Ruisui Tropic of Cancer Marker 20100204.jpg|Ruisui Tropic of Cancer Marker in Ruisui Township, Hualien County, Taiwan

File:Conghua toweroftropicofcancer.JPG|Tower of the Tropic of Cancer in Guangzhou, Guangdong Province, China

{{Portal|Geography|Africa|China|Mexico}}

• Circle of latitude
• Arctic Circle
• 24th parallel north
• 23rd parallel north
• Equator
• Tropic of Capricorn
• Antarctic Circle
• Axial tilt
• Milankovitch cycles

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{{Commons category|Tropic of Cancer}}

{{Wiktionary|Tropic of Cancer}}

• [http://www.jqjacobs.net/astro/epoch_2000.html Temporal Epoch Calculations]
• [http://hpiers.obspm.fr/eop-pc/models/constants.html Useful constants] (see: Obliquity of the ecliptic)

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