World map showing the Tropic of CancerRelationship of Earth's axial tilt (ε) to the tropical and polar circles
TheTropic of Cancer, also known as theNorthern Tropic,[citation needed] is theEarth's northernmostcircle of latitude where theSun can be seendirectly overhead. This occurs on theJune solstice, when theNorthern Hemisphere is tilted toward the Sun to its maximum extent.[1] It also reaches 90 degrees below the horizon at solar midnight on theDecember solstice. Using a continuously updated formula, the circle is currently 23°26′09.3″ (or 23.43593°) north of theEquator.
ItsSouthern Hemisphere counterpart, marking the most southerly position at which the Sun can be seen directly overhead, is theTropic of Capricorn. These tropics are two of the seven majorcircles of latitude that mark maps of Earth, the others being theArctic andAntarctic circles theEquator and thePoles (which are degenerate circles). The positions of these two circles of latitude (relative to the Equator) are dictated by the tilt of Earth'saxis of rotation relative to theplane of its orbit, and since the tilt changes, the location of these two circles also changes.
Ingeopolitics, it is known for being the southern limitation on the mutual defence obligation ofNATO, as member states of NATO are not obligated to come to the defence of territory south of the Tropic of Cancer.[2]
When this line of latitude was named in the last centuries BC, the Sun was in the constellationCancer (Latin:Crab) at theJune solstice (90°ecliptic longitude). Due to theprecession of the equinoxes, this is no longer the case; today the Sun is in the constellationTaurus at the June solstice. The word "tropic" itself comes from the Greek "trope (τροπή)", meaning turn (change of direction or circumstance) or inclination, referring to the fact that the Sun appears to "turn back" at the solstices.
Carretera 83 (Vía Corta) Zaragoza-Victoria, km 27+800. Of the Tropic of Cancer's intersections with Mexican federal highways, this was the only one where it is precisely marked and the drift from 2005 to 2010 could be seen. Nowadays, such signs no longer exist.
The Tropic of Cancer's position is not fixed, but constantly changes because ofaxial precession in the Earth's longitudinal alignment relative to theecliptic, 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[update] is about 23.4 degrees, which will continue to remain valid for about amillennium. 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 15 m (49 ft), per year. The circle's position was at exactly 23°27′N in 1917 and will be at 23°26'N in 2045.[3]
The distance between theAntarctic 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 andcircles of latitude for additional details.
Map all coordinates usingOpenStreetMapDownload coordinates asKML
North of the tropic are thesubtropics and theNorth Temperate Zone. The equivalent line of latitude south of the Equator is called theTropic of Capricorn, and the region between the two, centered on the Equator, is thetropics.
In the year 2000, more than half of the world's population lived north of the Tropic of Cancer.[4]
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 theprime 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, whereorographic rainfall can be very heavy, in some places reaching 4 metres (160 in) annually. Most regions on the Tropic of Cancer experience two distinct seasons: an extremely hot summer with temperatures often reaching 45 °C (113 °F) and a warm winter with maxima around 22 °C (72 °F). Much land on or near the Tropic of Cancer is part of theSahara Desert, while to the east, the climate is torridmonsoonal 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 isYu Shan inTaiwan. It had glaciers descending as low as 2,800 metres (9,190 ft) during theLast Glacial Maximum. At present glaciers still exist around[5] the Tropic. The nearest currently surviving are theMinyong andBaishui in theHimalayas to the north and onPico de Orizaba in Mexico to the south.
According to the rules of theFédération 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 allmeridians, and end on the same airfield where it started.
The length of the Tropic of Cancer is 36,788 km (22,859 mi):[6]
whereφ is the latitude of the Tropic of Cancer
For an ordinarycircumnavigation the rules are somewhat relaxed and the distance is set to a rounded value of at least 36,770 kilometres (22,850 mi).
Road sign south ofDakhla, marking the Tropic of Cancer. The sign was placed byBudapest-Bamako rally participants; thus, the inscription is in English andHungarian.
Road Sign near Mehsana City in Gujarat State, IndiaMehsana,Gujarat
Sign marking the Tropic of Cancer a few kilometres fromRann of Kutch,Gujarat, India
Sign marking the Tropic of Cancer inMadhya Pradesh, India
_Zaragoza-Victoria%2c_Km_27%252B800.jpg)
.svg)
