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Contents
1 Major circles of latitude
1.1 Equator 1.2 Polar Circles 1.3 Tropical Circles 1.4 Movement of the Tropical and Polar Circles
2 Other notable parallels 3 Altitude 4 See also 5 References 6 External links
Major circles of latitude[edit]
Diagram 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 circles
There 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[edit]
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.
Equator
Polar Circles[edit]
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 Circle
Tropical Circles[edit]
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 Capricorn
Movement of the Tropical and Polar Circles[edit]
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[edit]
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 Description
70°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'N
The 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 Chad
10°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.
Altitude[edit]
Note 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 also[edit]
List of circles of latitude
References[edit]
^ "''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 links[edit]
Wikimedia Commons has media related to Latitudes.
U.S. Naval Observatory - mean obliquity of the ecliptic
v t e
Circles of latitude / meridians
Equator 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 45x90
v t e
Ancient Greek astronomy
Astronomers
Aglaonice 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 Timocharis
Works
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)
Instruments
Antikythera mechanism Armillary sphere Astrolabe Dioptra Equatorial ring Gnomon Mural instrument Triquetrum
Concepts
Callippic cycle Celestial spheres Circle of latitude Counter-Earth Deferent and epicycle Equant Geocentrism Heliocentrism Hipparchic cycle Metonic cycle Octaeteris Solstice Spherical Earth Sublunary sphere Zodiac
Influences
Babylonian astronomy Egyptian astronomy
Influenced
Medieval European science Indian astronomy Medieval Islam