
The Tropic of Cancer, also known as the Northern Tropic, is the
Earth's northernmost
circle of latitude where the
Sun can be seen
directly overhead. This occurs on the
June solstice, when the
Northern Hemisphere 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
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
.
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
circles of latitude that mark maps of Earth, the others being the
Arctic
The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...
and
Antarctic circles and the
Equator
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
. 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, 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, the Sun was in the constellation
Cancer (
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
: ''
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.
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 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 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 , 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 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
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
,
axial tilt and
circles of latitude for additional details.
Geography
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.
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:
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 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, 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
Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...
. It had glaciers descending as low as during the
Last Glacial Maximum. At present glaciers still exist around 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.
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.
The length of the Tropic of Cancer is :
[Bakker et al., Radio Positioning at Sea: Geodetic Survey Computations Least Squares Adjustment, 1995 ()]
:
: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 .
Gallery
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
Madhya Pradesh (; ; ) is a state in central India. Its capital is Bhopal and the largest city is Indore, Indore. Other major cities includes Gwalior, Jabalpur, and Sagar, Madhya Pradesh, Sagar. Madhya Pradesh is the List of states and union te ...
, 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
Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...
File:Conghua toweroftropicofcancer.JPG, Tower of the Tropic of Cancer in Guangzhou
Guangzhou, Chinese postal romanization, previously romanized as Canton or Kwangchow, is the Capital city, capital and largest city of Guangdong Provinces of China, province in South China, southern China. Located on the Pearl River about nor ...
, Guangdong Province, China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
See also
*
Circle of latitude
**
Arctic Circle
The Arctic Circle is one of the two polar circles, and the northernmost of the five major circle of latitude, circles of latitude as shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle.
The Arctic Circl ...
**
24th parallel north
**
23rd parallel north
**
Equator
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
**
Tropic of Capricorn
**
Antarctic Circle
*
Axial tilt
*
Milankovitch cycles
References
External links
Temporal Epoch Calculations(see: Obliquity of the ecliptic)
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