View source for Tropic of Cancer

{{Short description|Line of northernmost latitude at which the Sun can be directly overhead}}
{{About|the circle of latitude}}
{{Coord|23|26|12.5|N|0|0|0|W|display=title|type:landmark|name=Prime Meridian}}
[[File:World map with tropic of cancer.svg|thumb|300px|World map showing the Tropic of Cancer]]
[[File:axial_tilt_vs_tropical_and_polar_circles.svg|thumb|350px|Relationship of Earth's axial tilt (ε) to the tropical and polar circles]]

The '''Tropic of Cancer''', also known as the '''Northern Tropic''', is the [[Earth]]'s northernmost [[circle of latitude]] where the [[Sun]] can be seen [[subsolar point|directly overhead]]. This occurs on the [[June solstice]], when the [[Northern Hemisphere]] is tilted toward the Sun to its maximum extent.<ref>{{cite web|title=Obliquity of the Ecliptic and Arctic Circle Calculator|url=https://www.phpsciencelabs.com/obliquity-of-the-ecliptic-calculator/|access-date=September 20, 2022}}</ref> It also reaches 90 degrees below the horizon at solar midnight on the [[December Solstice]]. Using a continuously updated formula, the circle is currently {{circle of latitude|tropical|convert}} north of the [[Equator]].

Its [[Southern Hemisphere]] counterpart, marking the most southerly position at which the Sun can be seen directly overhead, is the [[Tropic of Capricorn]]. These tropics are two of the five major [[circle of latitude|circles of latitude]] that mark maps of Earth, the others being the [[Arctic Circle|Arctic]] and [[Antarctic Circle|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 [[rotation around a fixed axis|axis of rotation]] relative to the [[orbital plane (astronomy)|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]], as member states of NATO are not obligated to come to the defence of territory south of the Tropic of Cancer.<ref>{{cite web |title=NATO - Topic: Collective defence and Article 5 |url=https://www.nato.int/cps/en/natohq/topics_110496.htm |publisher=North Atlantic Treaty Organization |access-date=4 April 2024}}</ref>

==Name==

When this line of latitude was named in the last centuries [[Common era|BCE]], the Sun was in the constellation [[Cancer (astrology)|Cancer]] ([[Latin]]: ''[[Crab]]'') at the [[June solstice]] (90° [[Ecliptic coordinate system#Ecliptic longitude|ecliptic longitude]]). Due to the [[axial precession|precession of the equinoxes]], this is no longer the case; today the Sun is in constellation [[Taurus (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.

==Drift==
[[File:Trópico de Cáncer en México - Carretera 83 (Vía Corta) Zaragoza-Victoria, Km 27+800.jpg|[[Mexican Federal Highway 83|Carretera 83]] (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.<ref>[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 }}</ref>

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#Geodesy|equator]], [[axial tilt]] and [[circle of latitude#Movement of the Tropical and Polar circles|circles of latitude]] for additional details.

==Geography==
{{kml}}
North of the tropic are the [[subtropics]] and the [[temperate climate|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.<ref>{{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}}</ref>

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:

{| class="wikitable plainrowheaders"
! scope="col" width="140" | Coordinates<br />([[Minute and second of arc|1']] accuracy ≈&nbsp;2&nbsp;km ≈&nbsp;1&nbsp;mi)
! scope="col" | Country, territory or sea
! scope="col" | Notes
|-
| {{Coord|23|26|N|0|0|E|type:landmark|name=Prime Meridian}}
! scope="row" | {{DZA}}
|
|-
| {{Coord|23|26|N|11|51|E|type:country|name=Niger}}
! scope="row" | {{NER}}
|
|-valign="top"
| {{Coord|23|26|N|12|17|E|type:country|name=Libya}}
! scope="row" | {{LBY}}
| The Tropic touches on the northernmost point of {{CHA}} at {{Coord|23|26|N|15|59|E|type:landmark|name=Northernmost point of Chad}}
|-valign="top"
| {{Coord|23|26|N|25|0|E|type:country|name=Egypt}}
! scope="row" | {{EGY}}
| The Tropic passes through [[Lake Nasser]]
|-
| style="background:#b0e0e6;" | {{Coord|23|26|N|35|30|E|type:waterbody|name=Red Sea}}
! scope="row" style="background:#b0e0e6;" | [[Red Sea]]
| style="background:#b0e0e6;" |
|-
| {{Coord|23|26|N|38|38|E|type:country|name=Saudi Arabia}}
! scope="row" | {{SAU}}
| [[Madinah Province|AlMedinah]], [[Makkah Province|Mecca]], [[Riyadh Province|ArRiyadh]], and [[Eastern Province, Saudi Arabia|The Eastern]] provinces.
|-
| {{Coord|23|26|N|52|10|E|type:country|name=United Arab Emirates}}
! scope="row" | {{ARE}}
| [[Abu Dhabi (Emirate)|Abu Dhabi]] emirate only 
|-
| {{Coord|23|26|N|55|24|E|type:country|name=Oman}}
! scope="row" | {{OMN}}
| The tropic crosses [[Muscat]], the country's capital.
|-
| style="background:#b0e0e6;" | {{Coord|23|26|N|58|46|E|type:waterbody|name=Indian Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Indian Ocean]]
| style="background:#b0e0e6;" | [[Arabian Sea]]
|-valign="top"
| {{Coord|23|26|N|68|23|E|type:country|name=India}}
! scope="row" | {{IND}}
| States of [[Gujarat]], [[Rajasthan]], [[Madhya Pradesh]], [[Chhattisgarh]], [[Jharkhand]] and [[West Bengal]] 
|-valign="tpo"
| {{Coord|23|26|N|88|47|E|type:country|name=Bangladesh}}
! scope="row" | {{BGD}}
| [[Khulna Division|Khulna]], [[Dhaka Division|Dhaka]], and [[Chittagong Division|Chittagong]] divisions
|-
| {{Coord|23|26|N|91|14|E|type:country|name=India}}
! scope="row" | {{IND}}
| State of [[Tripura]]
|-
| {{Coord|23|26|N|91|56|E|type:country|name=Bangladesh}}
! scope="row" | {{BGD}}
| [[Chittagong Division]]
|-
| {{Coord|23|26|N|92|19|E|type:country|name=India}}
! scope="row" | {{IND}}
| State of [[Mizoram]]
|-
| {{Coord|23|26|N|93|23|E|type:country|name=Myanmar}}
! scope="row" | {{MMR}}
| [[Chin State]], [[Sagaing Division]], [[Mandalay Division]], [[Shan State]]
|-valign="top"
| {{Coord|23|26|N|98|54|E|type:country|name=China}}
! scope="row" | {{CHN}}
| Provinces of [[Yunnan]] (passing about 7&nbsp;km north of the border with {{VNM}}), [[Guangxi]], and [[Guangdong]]
|-
| style="background:#b0e0e6;" | {{Coord|23|26|N|117|8|E|type:waterbody|name=Taiwan Strait}}
! scope="row" style="background:#b0e0e6;" | [[Taiwan Strait]]
| style="background:#b0e0e6;" |
|-valign="top"
| {{Coord|23|26|N|120|8|E|type:country|name=Taiwan}}
! scope="row" | {{TWN}}
| [[Hujing Island]] (Huching Island), [[Chiayi County]], [[Hualien County]]
|-valign="top"
| style="background:#b0e0e6;" | {{Coord|23|26|N|121|29|E|type:waterbody|name=Philippine Sea}}
! scope="row" style="background:#b0e0e6;" | [[Philippine Sea]]
| style="background:#b0e0e6;" | 
|-valign="top"
| style="background:#b0e0e6;" | {{Coord|23|26|N|142|00|E|type:waterbody|name=Pacific Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Pacific Ocean]]
| style="background:#b0e0e6;" | Passing just south of [[Necker Island (Hawaii)|Necker Island]], [[Hawaii]], {{USA}}
|-
| {{Coord|23|26|N|110|15|W|type:country|name=Mexico}}
! scope="row" | {{MEX}}
| State of [[Baja California Sur]]
|-
| style="background:#b0e0e6;" | {{Coord|23|26|N|109|24|W|type:waterbody|name=Gulf of California}}
! scope="row" style="background:#b0e0e6;" | [[Gulf of California]]
| style="background:#b0e0e6;" |
|-valign="top"
| {{Coord|23|26|N|106|35|W|type:country|name=Mexico}}
! scope="row" | {{MEX}}
| States of [[Sinaloa]], [[Durango]], [[Zacatecas]], [[San Luis Potosí]], [[Nuevo León]], and [[Tamaulipas]]
|-
| style="background:#b0e0e6;" | {{Coord|23|26|N|97|45|W|type:waterbody|name=Gulf of Mexico}}
! scope="row" style="background:#b0e0e6;" | [[Gulf of Mexico]]
| style="background:#b0e0e6;" |Passing just north of [[Cuba]]
|-valign="top"
| style="background:#b0e0e6;" | {{Coord|23|26|N|83|0|W|type:waterbody|name=Atlantic Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Atlantic Ocean]]
| style="background:#b0e0e6;" | Passing through the [[Straits of Florida]] and the [[Nicholas Channel]]<br/>Passing just south of the [[Cay Sal Bank|Anguilla Cays]] ({{BAH}})<br/>Passing through the [[Santaren Channel]] and into the open ocean
|-
| {{Coord|23|26|N|76|0|W|type:country|name=Bahamas}}
! scope="row" | {{BAH}}
| [[Exuma]] Islands and [[Long Island, Bahamas|Long Island]]
|-
| style="background:#b0e0e6;" | {{Coord|23|26|N|75|10|W|type:waterbody|name=Atlantic Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Atlantic Ocean]]
| style="background:#b0e0e6;" |
|-
| {{Coord|23|26|N|15|57|W|type:country|name=Western Sahara}}
! scope="row" | [[Western Sahara]]
| Claimed by {{MAR}} and the {{SADR}}
|-
| {{Coord|23|26|N|12|0|W|type:country|name=Mauritania}}
! scope="row" | {{MRT}}
|
|-
| {{Coord|23|26|N|6|23|W|type:country|name=Mali}}
! scope="row" | {{MLI}}
|
|-
| {{Coord|23|26|N|2|23|W|type:country|name=Algeria}}
! scope="row" | {{DZA}}
|
|-
|}

==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 [[Precipitation types#Orographic|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 [[monsoon]]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]] in [[Taiwan]]. It had glaciers descending as low as {{convert|2800|m|ft|-1}} during the [[Last Glacial Maximum]]. At present glaciers still exist around<ref>within {{convert|470|km|mi|-1}}</ref> the Tropic. The nearest currently surviving are the [[Minyong Glacier|Minyong]] and [[Baishui Glacier|Baishui]] in the [[Himalayas]] to the north and on [[Pico de Orizaba]] in Mexico 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 [[Meridian (geography)|meridians]], and end on the same airfield where it started.

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

:<math>l=2\pi \cos(\varphi) 6378137 (1-0.00669438(\sin(\varphi))^2)^{-0.5}</math>

: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}}.

==Gallery==
<gallery mode="packed">
File:Tropicofcancer.jpg|Road sign south of [[Dakhla, Western Sahara|Dakhla]], marking the Tropic of Cancer. The sign was placed by [[Budapest-Bamako]] rally participants; thus, the inscription is in English and [[Hungarian language|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|Ruisui Township]], [[Hualien County]], [[Taiwan]]
File:Conghua toweroftropicofcancer.JPG|Tower of the Tropic of Cancer in [[Guangzhou]], [[Guangdong Province]], [[China]]
</gallery>

== See also ==
{{Portal|Geography|Africa|China|Mexico}}

*[[Circle of latitude]]
**[[Arctic Circle]]
**[[24th parallel north]]
**[[23rd parallel north]]
**[[Equator]]
**[[Tropic of Capricorn]]
**[[Antarctic Circle]]
*[[Axial tilt#Earth|Axial tilt]]
*[[Milankovitch cycles]]

== References ==
{{reflist}}

== External links ==
{{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)

{{geographical coordinates |state = collapsed }}

[[Category:Circles of latitude|N23]]
[[Category:Tropics|Cancer of]]