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 A circle of latitude on Earth Earth is an abstract east–west circle connecting all locations around Earth Earth (ignoring elevation) at a given latitude. Circles of latitude are often called parallels because they are parallel to each other; that is, any two circles are always the same distance apart. A location's position along a circle of latitude is given by its longitude. Circles of latitude are unlike circles of longitude, which are all great circles with the centre of Earth Earth in the middle, as the circles of latitude get smaller as the distance from the Equator Equator increases. Their length can be calculated by a common sine or cosine function. The 60th parallel north 60th parallel north or south is half as long as the Equator Equator (disregarding Earth's minor flattening by 0.3%). A circle of latitude is perpendicular to all meridians. The latitude of the circle is approximately the angle between the Equator Equator and the circle, with the angle's vertex at Earth's centre. The equator is at 0°, and the North Pole North Pole and South Pole South Pole are at 90° north and 90° south, respectively. The Equator Equator is the longest circle of latitude and is the only circle of latitude which also is a great circle. There are 89 integral (whole degree) circles of latitude between the equator and the Poles in each hemisphere, but these can be divided into more precise measurements of latitude, and are often represented as a decimal degree (e.g. 34.637°N) or with minutes and seconds (e.g. 22°14'26"S). There is no limit to how precisely latitude can be measured, and so there are an infinite number of circles of latitude on Earth. On a map, the circles of latitude may or may not be parallel, and their spacing may vary, depending on which projection is used to map the surface of the Earth Earth onto a plane. On an equirectangular projection, centered on the equator, the circles of latitude are horizontal, parallel, and equally spaced. On other cylindrical and pseudocylindrical projections, the circles of latitude are horizontal and parallel, but may be spaced unevenly to give the map useful characteristics. For instance, on a Mercator projection Mercator projection the circles of latitude are more widely spaced near the poles to preserve local scales and shapes, while on a Gall–Peters projection Gall–Peters projection the circles of latitude are spaced more closely near the poles so that comparisons of area will be accurate. On most non-cylindrical and non-pseudocylindrical projections, the circles of latitude are neither straight nor parallel. Arcs of circles of latitude are sometimes used as boundaries between countries or regions where distinctive natural borders are lacking (such as in deserts), or when an artificial border is drawn as a "line on a map", which was made in massive scale during the 1884 Berlin Conference, regarding huge parts of the African continent. North American nations and states have also mostly been created by straight lines, which are often parts of circles of latitudes. For instance, the northern border of Colorado Colorado is at 41°N while the southern border is at 37°N. Roughly half the length of border between the United States and Canada Canada follows 49°N.Contents1 Major circles of latitude1.1 Equator 1.2 Polar Circles 1.3 Tropical Circles 1.4 Movement of the Tropical and Polar Circles2 Other notable parallels 3 Altitude 4 See also 5 References 6 External linksMajor circles of latitudeDiagram showing the locations of the five major circles of latitude on an equirectangular projection of the Earth.Relationship between Earth's axial tilt (ε) to the tropical and polar circlesThere are five major circles of latitude, listed below from north to south. The position of the Equator Equator is fixed (90 degrees from Earth's axis of rotation) but the latitudes of the other circles depend on the tilt of this axis relative to the plane of Earth's orbit, and so are not perfectly fixed. The values below are for 3 April 2018:[1] Arctic Circle Arctic Circle (66°33′47.1″ N) Tropic of Cancer Tropic of Cancer (23°26′12.9″ N) Equator Equator (0° latitude) Tropic of Capricorn Tropic of Capricorn (23°26′12.9″ S) Antarctic Circle Antarctic Circle (66°33′47.1″ S)These circles of latitude, excluding the Equator, mark the divisions between the five principal geographical zones. Equator The equator is the circle that is equidistant from the North Pole North Pole and South Pole. It divides the Earth Earth into the Northern Hemisphere Northern Hemisphere and the Southern Hemisphere. Of the parallels or circles of latitude, it is the longest, and the only 'great circle' (a circle on the surface of the Earth, centered on Earth's center). All the other parallels are smaller and centered only on Earth's axis.EquatorPolar Circles The Arctic Circle Arctic Circle is the southernmost latitude in the Northern Hemisphere at which the sun can remain continuously above or below the horizon for 24 hours (at the June and December solstices respectively). Similarly, the Antarctic Circle Antarctic Circle marks the northernmost latitude in the Southern Hemisphere Southern Hemisphere at which the sun can remain continuously above or below the horizon for 24 hours (at the December and June Solstices respectively).Arctic Circle Antarctic CircleTropical Circles The Tropic of Cancer Tropic of Cancer and Tropic of Capricorn Tropic of Capricorn mark the northernmost and southernmost latitudes at which the sun may be seen directly overhead (at the June solstice and December solstice December solstice respectively). The latitude of the tropical circles is equal to the Earth's axial tilt, about 23°.Tropic of Cancer Tropic of CapricornMovement of the Tropical and Polar Circles See also: Axial tilt By definition, the positions of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle Arctic Circle and Antarctic Circle Antarctic Circle all depend on the tilt of the Earth's axis relative to the plane of its orbit around the sun (the "obliquity of the ecliptic"). If the Earth Earth were "upright" (its axis at right angles to the orbital plane) there would be no Arctic, Antarctic, or Tropical circles: at the poles the sun would always circle along the horizon, and at the equator the sun would always rise due east, pass directly overhead, and set due west. The positions of the Tropical and Polar Circles are not fixed because the axial tilt changes slowly – a complex motion determined by the superimposition of many different cycles (some of which are described below) with short to very long periods. In 2000 the mean value of the tilt was about 23° 26′ 21″. The main long-term cycle causes the axial tilt to fluctuate between about 22.1° and 24.5° with a period of 41,000 years. Currently, the average value of the tilt is decreasing by about 0.47″ per year. As a result, (approximately, and on average) the Tropical Circles are drifting towards the equator (and the Polar Circles towards the poles) by 15 metres per year, and the area of the Tropics Tropics is decreasing by 1,100 square kilometres (420 sq mi) per year. The Earth's axial tilt has additional shorter-term variations due to nutation, of which the main term, with a period of 18.6 years, has an amplitude of 9.2" (corresponding to almost 300 metres north and south).[2] There are many smaller terms, resulting in varying daily shifts of some metres in any direction. Finally, the Earth's rotational axis is not exactly fixed in the Earth, but undergoes small fluctuations (on the order of 15 meters) called polar motion, which have a small effect on the Tropics Tropics and Polar Circles and also on the Equator. Short-term fluctuations over a matter of days do not directly affect the location of the extreme latitudes at which the sun may appear directly overhead, or at which 24-hour day or night is possible, except when they actually occur at the time of the solstices. Rather, they cause a theoretical shifting of the parallels, that would occur if the given axis tilt were maintained throughout the year. Other notable parallels See also: Baseline (surveying) A number of sub-national and international borders were intended to be defined by, or are approximated by, parallels. Parallels make convenient borders in the northern hemisphere because astronomic latitude can be roughly measured (to within a few tens of meters) by sighting the North Star.Parallel Description70°N On Victoria Island, Canada, two sections of the border between Northwest Territories Northwest Territories and Nunavut.60°N In Canada, the southern border of Yukon Yukon with the northern border of British Columbia; the southern border of Northwest Territories Northwest Territories with the northern borders of British Columbia, Alberta Alberta and Saskatchewan; and the southern border of mainland Nunavut Nunavut with the northern border of Manitoba, leading to the expression "north of sixty" for the territories.54°40'N The border between 19th century Russian territories to the north and conflicting American and British land claims in western North America. The conflicting claims led to the Oregon boundary dispute Oregon boundary dispute between Britain and the United States, giving rise to the slogan "Fifty-four forty or fight."52°N In Canada, part of the border between Newfoundland and Labrador Newfoundland and Labrador and Quebec.51°N The southern limit of Russian America Russian America from 1799 to 1821.49°N Much of the border between Canada Canada and the United States, from British Columbia to Manitoba; "49th parallel" is a common expression for the border, though the majority of Canada's population actually lives south of the parallel.48°N In Canada, part of the border between Quebec Quebec and New Brunswick.46°N In the United States, part of the border between Washington and Oregon.45°N Part of the border between Canada Canada (Quebec) and the USA (New York and Vermont) is approximated by the parallel. Also, in the USA, it approximates most of the border between Montana Montana and Wyoming.43°30'N In the USA, the border between Minnesota Minnesota and Iowa.43°N In the USA, much of the border between South Dakota South Dakota and Nebraska.42°30'N In the USA, the border between Wisconsin Wisconsin and Illinois.42°N Originally the northward limit of New Spain. In the USA, the southern borders of Oregon Oregon and Idaho Idaho where they meet the northern borders of California, Nevada Nevada and Utah. The parallel also defines much of the border between Pennsylvania Pennsylvania and New York.41°N In the USA, part of the border between Wyoming Wyoming and Utah, the border between Wyoming Wyoming and Colorado, and part of the border between Nebraska and Colorado.40°N In the USA, the border between Nebraska Nebraska and Kansas. The parallel was originally chosen for the Mason–Dixon line, but the line was moved several miles south to avoid bisecting the city of Philadelphia.38°N The boundary between the Soviet and American occupation zones in Korea, and later between North Korea North Korea and South Korea, from 1945 until the Korean War Korean War (1950–1953).37°N In the USA, the southern border of Utah Utah with the northern border of Arizona. The southern border of Colorado Colorado with the northern borders of New Mexico New Mexico and Oklahoma. The southern border of Kansas Kansas with the northern border of Oklahoma.36°30'NThe historic Missouri Compromise Missouri Compromise line. In the USA, defines part of the border between Oklahoma Oklahoma and Texas, most of the border between Missouri and Arkansas. Geographically it is a Westward extension of the border between Virginia Virginia and North Carolina North Carolina and part of the border between Kentucky Kentucky and Tennessee.36°N In the USA, a short section of the border between the Missouri Bootheel and Arkansas.35°N In the USA, the southern border of Tennessee, which meets Mississippi, Alabama Alabama and Georgia. Also, part of the border between North Carolina and Georgia.33°N In the USA, the southern border of Arkansas, which meets the northern border of Louisiana, is approximated by the parallel. Historically, it defined the southern border of the Louisiana Louisiana Territory.32°N In the USA, part of the border between New Mexico New Mexico and Texas.31°20'N Part of the border between the USA and Mexico Mexico ( Sonora Sonora and Chihuahua); the southern border of Arizona Arizona and the New Mexico New Mexico Bootheel.31°N Part of the border between Iran Iran and Iraq. In the USA, part of the border between Mississippi Mississippi and Louisiana, and part of the border between Alabama Alabama and Florida.28°N In Mexico, the border between Baja California California and Baja California California Sur.26°N Part of the border between Western Sahara Western Sahara (claimed by Morocco) and Mauritania.25°N Part of the border between Mauritania Mauritania and Mali.22°N Much of the border between Egypt Egypt and Sudan, partly disputed (see also Hala'ib Triangle).20°N A short section of the border between Libya Libya and Sudan, and within Sudan, the northern border of the Darfur Darfur region.17°N The division between Republic of Vietnam (South Vietnam) and Democratic Republic of Vietnam (North Vietnam) during the Vietnam War.15°N de facto maritime border between Honduras Honduras and Nicaragua.[3]13°05'N Part of the border between Chad Chad and Cameroon, over a stretch of 41.6 km, partly in Lake Chad10°N Part of the border between Guinea Guinea and Sierra Leone.8°N Part of the border between Somalia Somalia and Ethiopia.1°N Part of the border between Equatorial Guinea Guinea and Gabon.1°S Most of the border between Uganda Uganda and Tanzania, and a very short section of the border between Kenya Kenya and Tanzania Tanzania in Lake Victoria.7°S A short section of the border between Democratic Republic of the Congo and Angola.8°S Two short sections of the border between Democratic Republic of the Congo and Angola.10°S A short section of the border between Brazil Brazil and Peru.13°S Part of the border between Angola Angola and Zambia.16°S Part of the border between Mozambique Mozambique and Zimbabwe.22°S A short section of the border between Namibia Namibia and Botswana, and parts of the border between Bolivia Bolivia and Argentina.26°S In Australia, the border between South Australia Australia and the Northern Territory, and part of the border between South Australia Australia and Queensland.28°S In Argentina, the border between Chaco Province Chaco Province and Santa Fe Province.29°S In Australia, much of the border between Queensland Queensland and New South Wales.35°S In Argentina, part of the border between Córdoba Province and La Pampa Province.36°S In Argentina, part of the border between Mendoza Province Mendoza Province and La Pampa Province, and part of the border between San Luis Province San Luis Province and La Pampa Province.42°S In Argentina, the border between Río Negro Province Río Negro Province and Chubut Province.46°S In Argentina, the border between Chubut Province Chubut Province and Santa Cruz Province.52°S Part of the border between Argentina Argentina and Chile.60°S The northern boundary of Antarctica Antarctica for the purposes of the Antarctic Treaty System (see map). The northern boundary of the Southern Ocean.AltitudeNote that the features of the spheroid cross-section (orange) in this image are exaggerated with respect to the Earth.Altitude has an effect on a location's position relative to the plane formed by a circle of latitude. Since altitude is determined by the normal to the Earth's surface, locations sharing the same latitude—but having different elevations (e.g., lying along this normal)—no longer lie within this plane. Rather, all points sharing the same latitude and of varying elevation occupy a cone formed by the rotation of this normal around the Earth's axis. See alsoList of circles of latitudeReferences^ "''Trópico en movimiento'' (in Spanish)". Groups.google.com. Retrieved 2014-05-13.  ^ "Basics of Space Flight, Chapter 2". Jet Propulsion Laboratory. Jet Propulsion Laboratory/NASA. 2013-10-29. Retrieved 2015-03-26.  ^ "Maritime Delimitation between Nicaragua Nicaragua and Honduras Honduras in the Caribbean Sea ( Nicaragua Nicaragua v. Honduras)" (PDF). Retrieved 2014-05-13. External linksWikimedia Commons has media related to Latitudes.U.S. Naval Observatory - mean obliquity of the eclipticv t eCircles of latitude / meridiansEquator Tropic of Cancer Tropic of Capricorn Arctic Circle Antarctic Circle Equator Tropic of Cancer Tropic of Capricorn Arctic Circle Antarctic Circle Equator Tropic of Cancer Tropic of Capricorn Arctic Circle Antarctic Circle W 0° E 30° 60° 90° 120° 150° 180° 30° 60° 90° 120° 150° 180° 5° 15° 25° 35° 45° 55° 65° 75° 85° 95° 105° 115° 125° 135° 145° 155° 165° 175° 5° 15° 25° 35° 45° 55° 65° 75° 85° 95° 105° 115° 125° 135° 145° 155° 165° 175° 10° 20° 40° 50° 70° 80° 100° 110° 130° 140° 160° 170° 10° 20° 40° 50° 70° 80° 100° 110° 130° 140° 160° 170° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 10° 20° 30° 40° 50° 60° 70° 80° 90° 5° N 15° 25° 35° 45° 55° 65° 75° 85° 5° S 15° 25° 35° 45° 55° 65° 75° 85° 45x90 45x90 45x90 45x90v t eAncient Greek astronomyAstronomersAglaonice Agrippa Anaximander Andronicus Apollonius Aratus Aristarchus Aristyllus Attalus Autolycus Bion Callippus Cleomedes Cleostratus Conon Eratosthenes Euctemon Eudoxus Geminus Heraclides Hicetas Hipparchus Hippocrates of Chios Hypsicles Menelaus Meton Oenopides Philip of Opus Philolaus Posidonius Ptolemy Pytheas Seleucus Sosigenes of Alexandria Sosigenes the Peripatetic Strabo Thales Theodosius Theon of Alexandria Theon of Smyrna TimocharisWorks Almagest Almagest (Ptolemy) On Sizes and Distances On Sizes and Distances (Hipparchus) On the Sizes and Distances (Aristarchus) On the Heavens On the Heavens (Aristotle)InstrumentsAntikythera mechanism Armillary sphere Astrolabe Dioptra Equatorial ring Gnomon Mural instrument TriquetrumConceptsCallippic cycle Celestial spheres Circle of latitude Counter-Earth Deferent and epicycle Equant Geocentrism Heliocentrism Hipparchic cycle Metonic cycle Octaeteris Solstice Spherical Earth Sublunary sphere ZodiacInfluencesBabylonian astronomy Egyptian astronomyInfluencedMedieval European science Indian astronomy Medieval

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