What is "circle of latitude"

Latitude \Lat"i*tude\, n. [F. latitude, L. latitudo, fr. latus broad, wide, for older stlatus; perh. akin to E. strew.]

1. Extent from side to side, or distance sidewise from a given point or line; breadth; width.

   Provided the length do not exceed the latitude above one third part.
   --Sir H. Wotton.

2. Room; space; freedom from confinement or restraint; hence, looseness; laxity; independence.

   In human actions there are no degrees and precise natural limits described, but a latitude is indulged.
   --Jer. Taylor.

3. Extent or breadth of signification, application, etc.; extent of deviation from a standard, as truth, style, etc.

   No discreet man will believe Augustine's miracles, in the latitude of monkish relations.
   --Fuller.

4. Extent; size; amplitude; scope.

   I pretend not to treat of them in their full latitude.
   --Locke.

5. (Geog.) Distance north or south of the equator, measured on a meridian.

6. (Astron.) The angular distance of a heavenly body from the ecliptic.

   Ascending latitude, Circle of latitude, Geographical latitude, etc. See under Ascending. Circle, etc.

   High latitude, that part of the earth's surface near either pole, esp. that part within either the arctic or the antarctic circle.

   Low latitude, that part of the earth's surface which is near the equator.

Circle \Cir"cle\ (s[~e]r"k'l), n. [OE. cercle, F. cercle, fr. L. circulus (Whence also AS. circul), dim. of circus circle, akin to Gr. kri`kos, ki`rkos, circle, ring. Cf. Circus, Circum-.]

1. A plane figure, bounded by a single curve line called its circumference, every part of which is equally distant from a point within it, called the center.

2. The line that bounds such a figure; a circumference; a ring.

3. (Astron.) An instrument of observation, the graduated limb of which consists of an entire circle.

   Note: When it is fixed to a wall in an observatory, it is called a mural circle; when mounted with a telescope on an axis and in Y's, in the plane of the meridian, a meridian circle or transit circle; when involving the principle of reflection, like the sextant, a reflecting circle; and when that of repeating an angle several times continuously along the graduated limb, a repeating circle.

4. A round body; a sphere; an orb.

   It is he that sitteth upon the circle of the earth.
   --Is. xi. 22.

5. Compass; circuit; inclosure.

   In the circle of this forest.
   --Shak.

6. A company assembled, or conceived to assemble, about a central point of interest, or bound by a common tie; a class or division of society; a coterie; a set.

   As his name gradually became known, the circle of his acquaintance widened.
   --Macaulay.

7. A circular group of persons; a ring.

8. A series ending where it begins, and repeating itself.

   Thus in a circle runs the peasant's pain.
   --Dryden.

9. (Logic) A form of argument in which two or more unproved statements are used to prove each other; inconclusive reasoning.

   That heavy bodies descend by gravity; and, again, that gravity is a quality whereby a heavy body descends, is an impertinent circle and teaches nothing.
   --Glanvill.

10. Indirect form of words; circumlocution. [R.]

    Has he given the lie, In circle, or oblique, or semicircle.
    --J. Fletcher.

11. A territorial division or district. Note: The Circles of the Holy Roman Empire, ten in number, were those principalities or provinces which had seats in the German Diet. Azimuth circle. See under Azimuth. Circle of altitude (Astron.), a circle parallel to the horizon, having its pole in the zenith; an almucantar. Circle of curvature. See Osculating circle of a curve (Below). Circle of declination. See under Declination. Circle of latitude.

    1. (Astron.) A great circle perpendicular to the plane of the ecliptic, passing through its poles.

    2. (Spherical Projection) A small circle of the sphere whose plane is perpendicular to the axis.

       Circles of longitude, lesser circles parallel to the ecliptic, diminishing as they recede from it.

       Circle of perpetual apparition, at any given place, the boundary of that space around the elevated pole, within which the stars never set. Its distance from the pole is equal to the latitude of the place.

       Circle of perpetual occultation, at any given place, the boundary of the space around the depressed pole, within which the stars never rise.

       Circle of the sphere, a circle upon the surface of the sphere, called a great circle when its plane passes through the center of the sphere; in all other cases, a small circle.

       Diurnal circle. See under Diurnal.

       Dress circle, a gallery in a theater, generally the one containing the prominent and more expensive seats.

       Druidical circles (Eng. Antiq.), a popular name for certain ancient inclosures formed by rude stones circularly arranged, as at Stonehenge, near Salisbury.

       Family circle, a gallery in a theater, usually one containing inexpensive seats.

       Horary circles (Dialing), the lines on dials which show the hours.

       Osculating circle of a curve (Geom.), the circle which touches the curve at some point in the curve, and close to the point more nearly coincides with the curve than any other circle. This circle is used as a measure of the curvature of the curve at the point, and hence is called circle of curvature.

       Pitch circle. See under Pitch.

       Vertical circle, an azimuth circle.

       Voltaic circuit or Voltaic circle. See under Circuit.

       To square the circle. See under Square.

       Syn: Ring; circlet; compass; circuit; inclosure.

A circle of latitude on the Earth is an imaginary east- west circle connecting all locations (ignoring elevation) with a given latitude. A location's position along a circle of latitude is given by its longitude.

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. Unlike circles of longitude, which all are great circles with the centre of Earth in the middle, the circles of latitude get smaller as the distance from the Equator increases. Their length can be calculated by a common sine or cosine function. The 60th circle of latitude is half as long as the equator (disregarding Earth’s minor ovality, which is less than 0.3%). A circle of latitude is perpendicular to all meridians.

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 Pole are at 90° north and 90° south respectively. The 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 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 the circles of latitude are more widely spaced near the poles to preserve local scales and shapes, while on a 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 1888 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 is at 41°N while the southern border is at 37°N. Roughly half the length of border between the United States and Canada follows 49°N.