Lena Rivera
The Earth is divided into five major circles of latitude, also known as parallels, which run parallel to the equator and connect all locations with the same latitude coordinate. The equator is the longest circle of latitude and the only great circle, meaning it passes through the exact centre of the Earth and divides it into two equal halves. The other four circles of latitude are smaller and centred on the Earth's axis. These circles of latitude are important for navigation, as they represent the shortest distance between two points on a sphere, and for defining international borders.
| Characteristics | Values |
|---|---|
| Definition | Circles of latitude or lines of latitude on Earth are abstract east-west small circles connecting all locations around the Earth (ignoring elevation) at a given latitude coordinate line. |
| Other names | Parallels, lines of latitude |
| Reference plane | The reference plane for all circles of latitude is the equatorial circle of latitude that bisects the Earth. |
| Length | The length of a circle of latitude can be calculated by a common sine or cosine function. The length of the equator, the largest circle of latitude, is about 40,000 km (24,854-24,901miles) depending on the source. |
| Relationship with longitude | Circles of latitude are perpendicular to all longitudes at their intersection points. |
| Relationship with elevation | Circles of latitude are defined at zero elevation. |
| Borders | Parallels make convenient borders in the northern hemisphere because astronomic latitude can be roughly measured by sighting the North Star. |
| Notable circles of latitude | The equator, the Arctic Circle, the Antarctic Circle, the Tropic of Cancer, and the Tropic of Capricorn. |
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What You'll Learn
- Circles of latitude are neither straight nor parallel on most projections
- The equator is the only great circle and the only east-west line
- Circles of latitude are often used for borders between countries or regions
- The shortest path between two points on Earth is a segment of a great circle
- The Equator is the reference point for latitude, denoted as 0° latitude
Circles of latitude are neither straight nor parallel on most projections
Circles of latitude, also known as parallels, are abstract east-west small circles connecting all locations around the Earth (ignoring elevation) at a given latitude coordinate line. They are often called parallels because they are parallel to each other; planes that contain any of these circles never intersect. The equator is the only circle of latitude that is a great circle, meaning it passes through the exact centre of the Earth and divides it into two equal halves: the Northern and Southern Hemispheres.
However, on most non-cylindrical and non-pseudocylindrical projections, the circles of latitude are neither straight nor parallel. On an equirectangular projection, centred 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 example, on a Mercator projection, the circles of latitude are more widely spaced near the poles to preserve local scales and shapes. In contrast, on a Gall-Peters projection, the circles of latitude are spaced more closely near the poles so that comparisons of area are accurate.
The placement of parallels on a map projection can be determined by an algorithm chosen by the designer to suit the needs of the map. For instance, the famous Mercator projection uses an algorithm that places parallels to satisfy the property that a course of constant bearing is always plotted as a straight line. In reality, the curved line on a great circle route is actually shorter than a straight line along the same route, but it appears longer on a Mercator map.
The number of circles of latitude between the Equator and the poles in each hemisphere is 89 integral (whole degree) circles, but these can be divided into more precise measurements, often represented as decimal degrees or with minutes and seconds. The latitude of the circle is approximately the angle between the Equator and the circle, with the angle's vertex at the Earth's centre. The Equator is at 0°, and the North and South Poles are at 90° north and 90° south, respectively.
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The equator is the only great circle and the only east-west line
The Earth is not a perfect sphere but an oblate spheroid, with a slight bulge around the Equator. The Equator is an imaginary circle that is equidistant from the North and South Poles, dividing the Earth into the Northern and Southern Hemispheres. It is the only great circle of latitude, or line of latitude, that passes through the Earth's centre and divides the planet into two equal halves. All other parallels or lines of latitude are smaller and centred on the Earth's axis, getting smaller as they approach the poles.
The Equator is also the only east-west line that is a great circle. It is the only line of latitude that is the same length as its corresponding line on the opposite side of the Earth, which together form a full great circle. All other lines of latitude are not great circles as their length decreases towards the poles and they do not pass through the Earth's centre.
Great circles are important in navigation as they represent the shortest distance between two points on a sphere. They have been used for hundreds of years, although sailors and pilots must constantly adjust their route due to the Earth's rotation. The Equator is one of the only places on Earth where the heading does not change, the others being when travelling due north or south.
The length of the Equator is approximately 40,000 kilometres (24,855-24,901 miles) and it is the only great circle with a consistent heading. It is also the only great circle that is perpendicular to the Earth's axis.
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Circles of latitude are often used for borders between countries or regions
Circles of latitude, also known as parallels, are abstract east-west circles that connect all places with the same latitude. They are often used as boundaries between countries or regions, especially where distinctive natural borders are lacking, such as in deserts. For example, the northern border of Colorado is at 41° N, while the southern border is at 37° N. The Equator is the only line of latitude that is a great circle, meaning it passes through the exact centre of the Earth and divides it into two equal halves: the Northern and Southern Hemispheres. All other parallels are smaller and centred on the Earth's axis. The Equator is also the only parallel that is equidistant from the North and South Poles.
The five major parallels of latitude from north to south are the Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn, and the Antarctic Circle. The Arctic Circle is the southernmost latitude in the Northern Hemisphere where the Sun can remain continuously above or below the horizon for 24 hours (at the June and December solstices). Similarly, the Antarctic Circle is the northernmost latitude in the Southern Hemisphere with this characteristic. The Tropics of Cancer and Capricorn also fluctuate depending on the Earth's axial tilt. The Tropic of Capricorn is the parallel where the Winter (or Southern or December) Solstice occurs, and the sun appears directly overhead the most southerly parallel.
Parallels make convenient borders in the Northern Hemisphere because astronomic latitude can be roughly measured by sighting the North Star. The use of parallels as borders was particularly prominent during the 1884 Berlin Conference, where artificial borders were drawn on a large scale for 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, roughly half the length of the border between the United States and Canada follows 49° N.
Great circles, including the Equator, are also important in navigation as they represent the shortest distance between two points on the surface of a sphere. They have been used for hundreds of years, although they were only discovered by ancient mathematicians.
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The shortest path between two points on Earth is a segment of a great circle
The Earth is not a perfect sphere; it is an oblate spheroid, stretching slightly around the Equator. The Equator is the only great circle that is a parallel circle of latitude. All other parallels of latitude are smaller and centred on the Earth's axis, not its centre. The Equator is the longest circle of latitude and the only one that is a great circle.
A great circle is the largest possible circle that can be drawn on the surface of a sphere. It is formed by the intersection of the sphere with a plane that passes through the sphere's centre. A great circle divides a sphere into two equal halves or hemispheres. The Earth's circumference along a great circle is about 40,000 kilometres (24,854-24,855 miles) in length along meridians.
Great circle routes are also used by pilots flying planes. If you flew from Atlanta, Georgia, in the United States, to Athens, Greece, you would fly roughly along the path of one of Earth's great circles. In the northern hemisphere, planes travelling west often follow a great circle route that moves into the Arctic to avoid flying against the jet stream.
Great circle routes are useful because maps distort the true geometry of the Earth. Flat maps or Mercator maps, for example, do not accurately represent the Earth's spherical shape. On such maps, great circle routes appear curved and longer than straight lines along the same routes. However, the curved line is actually shorter because it follows the great circle route.
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The Equator is the reference point for latitude, denoted as 0° latitude
The Equator is an imaginary circle that runs around the Earth, equidistant from the geographic North and South Poles. It divides the Earth into the Northern and Southern Hemispheres.
Lines of latitude north of the Equator are numbered from 1° to 89° N, and those south of the Equator are numbered from 1° to 89° S. Latitude is usually measured in degrees (°), which can be broken down into smaller units called minutes (') and seconds ("). For example, a location's latitude can be given as 50°39.734' N 001°35.500' W. This indicates that the position is 50 degrees, 39 minutes, and 734 seconds north of the Equator and 1 degree, 35 minutes, and 500 seconds west of the Prime Meridian.
The Equator is the only line of latitude that is a great circle, meaning it passes through the exact centre of the Earth and divides it into two equal halves. All other lines of latitude are smaller and centred on the Earth's axis, becoming smaller as they approach the poles. The Earth's circumference at the Equator is approximately 40,075 km (24,901 mi), slightly longer than the polar circumference of about 40,008 km (24,860 mi).
The Equator serves as the primary reference line for latitude, with the parallels or circles of latitude running parallel to it. These parallels are used to determine the latitude coordinates of any location on Earth, providing a global framework for navigation and geographic understanding.
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Frequently asked questions
There is only one parallel circle, the equator, which is the only great circle and the only east-west line. All other parallels or circles of latitude are smaller and centered on the Earth's axis.
A great circle is any circle drawn on a sphere with a center that includes the center of the sphere. On Earth, great circles are about 40,000 kilometers (24,854-24,901 miles) in length along meridians.
Circles of latitude are imaginary east-west circles that connect all places with the same latitude. They are often called parallels because they are parallel to each other and to the equator.
Circles of latitude are used to define sub-national and international borders. They are also used for navigation as they represent the shortest distance between two points on a sphere.
