A mechanism of present is used to discover the ar of any type of place on the surface of the Earth. Commonly called a network system, that is consisted of of two sets of lines that cross every other. One set—lines the latitude—runs in one east-west direction. The other set—lines the longitude—runs in a north-south direction. Although this are just imaginary currently encircling the Earth, they can be attracted on globes and also maps as if they actually existed.

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Drawing the planet Grid

To draw the present of the grid system on a world or map, that is essential to have starting points, or point out of reference. There are two together points of reference on the Earth. These room the north Pole and also the south Pole. The poles are the points in ~ which the earth axis meets the earth’s surface. Halfway between the poles is one east-west line called the equator. The encircles the Earth and also divides it right into two same parts, or hemispheres. The phibìc Pole is in the hemisphere phibìc of the equator—the north Hemisphere. The south Pole is in the hemisphere south of the equator—the southerly Hemisphere.


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One set of present in the earth’s grid mechanism is drawn roughly the globe parallel come the equator. These are east-west lines, or currently of latitude. In the straightforward grid there space 89 such equally spaced lines come the phibìc of the equator, 89 to the south. Whereby the 90th east-west lines would be are two points—the North and South poles. Each east-west line is a circle. The farther that is from the equator the much shorter its length. The 60th east-west line, for example, is only fifty percent as long as the equator.

East-west lines are numbered from 0 in ~ the equator—the east-west base line—to 89 close to the poles. The east-west lines in between the equator and also the north Pole space north that the equator; those between the equator and the southern Pole, south of the equator. The city of new Orleans, Louisiana, is situated on the 30th east-west line north of the equator. But many other areas in the people are additionally situated ~ above this line. The is why a 2nd set of currently is essential to locate the precise position of brand-new Orleans—or of any type of other place.


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The 2nd set of lines in the earth’s grid mechanism is drawn from pole come pole. These are north-south lines, or present of longitude. One north-south line has actually been preferred by international agreement as the zero, or base line. That passes with Greenwich, England, a borough the London. In the basic grid there space 180 together equally spaced lines to the eastern of the Greenwich base line, 180 to the west. Uneven east-west lines, every north-south lines have actually the very same length.

North-south lines room numbered from 0 at the north-south base heat both east and west to the 180th north-south line. The zero line and the 180th line together form a complete circle that, favor the equator, cut the earth into 2 hemispheres. The half west that the zero line can be referred to as the west Hemisphere; the half east the the zero line, the east Hemisphere.


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The north-south lines and the east-west lines together kind the global grid device used to uncover the precise location of any kind of place ~ above Earth. New Orleans, on the 30th east-west line north the the equator, is additionally on the 90th north-south line west that the north-south base line. Plenty of places in the world—among them, Memphis, Tennessee; eastern St. Louis, Illinois; and also the Galápagos islands of Ecuador—are top top or near the exact same north-south line as brand-new Orleans. Many other places—for example, port Arthur, Texas; St. Augustine, Florida; and also Cairo, Egypt—are top top or close to the very same east-west line as new Orleans. But only brand-new Orleans is positioned on both lines—exactly wherein they cross every other. Likewise, each location in the world—and only that place—is positioned at the intersection of a provided east-west line and a offered north-south line.

Parallels and also Meridians

All east-west lines are equidistant from each other. This method that they are all parallel to the equator and also to every other. Every point on a given east-west line, therefore, is the exact same distance from the equator, the very same distance native the phibìc Pole, and the same distance native the southern Pole. For this reason east-west lines, or currently of latitude, are typically referred to together parallels that latitude, or just parallels.

The north-south lines, or currently of longitude, likewise have another name. Lock are generally referred to as meridians of longitude, or just meridians. The zero meridian, or base line because that numbering the north-south lines, is called the prime meridian.

Each meridian goes just halfway around the Earth—from pole come pole. Each has a pair on the other side that the Earth. Like the prime meridian and also the 180th meridian, every such bag of meridians kind circles that cut the planet into hemispheres. This circles are known as great circles. Just one parallel, the equator, is a great circle.

Measurements of Angular Distance


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A cutaway illustration of the planet demonstrates just how latitude is determined. It provides clear the latitude is a measure up of the angle in between the aircraft of the equator and also lines projected from the facility of the Earth. For example, the angle between a line drawn from brand-new Orleans on the 30th line of latitude come the center of the Earth and a line drawn on the airplane of the equator is 30 degrees (30°). In each hemisphere the 30th heat of latitude connects all points who projections to the facility of the Earth kind a 30° angle with the aircraft of the equator.

The latitude the the equator is zero degrees (0°). Lines of latitude north and also south of the equator space numbered come 90° since the angular street from the equator to every pole is one-fourth that a circle, or one-fourth the 360°. Over there is no latitude higher than 90°. The phibìc Pole is situated at 90° phibìc latitude, or simply 90° N. The south Pole is at 90° south latitude, or 90° S.

The cutaway drawing of the Earth additionally shows just how longitude is determined. Longitude is watched to be a measure of the angle between the planes of two meridian circles, one of which is the prime meridian. For example, the airplane of the 90th line of longitude, on which new Orleans is located, forms a 90° angle with the aircraft of the element meridian. All places on the 90th line of longitude west that the element meridian, therefore, room at 90° west longitude.

The prime meridian is designated zero degrees (0°) longitude. Lines of longitude are numbered eastern of the prime meridian from 0° come 180° eastern longitude and also west from 0° come 180° west longitude. There is no longitude higher than 180°, and also the 180th meridian east and also the 180th meridian west space identical.


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Degrees that latitude and also longitude have the right to be separated into sixtieths, or minutes (′). Any kind of location on planet can be defined as lying in ~ a certain variety of degrees and also minutes of latitude either north or southern of the equator and at a certain variety of degrees and minutes the longitude either east or west the the prime meridian. For example, the United claims Capitol in Washington, D.C., is at 38 levels 53 minutes north latitude (38°53′ N.) and 77 degrees 0 minutes west longitude (77°0′ W.). Minute of latitude and also longitude can be separated into sixtieths, or secs (″), when an ext precise info on the location of a ar is needed, because that example, by navigators, surveyors, pilots, or map makers.

A level of latitude can conveniently be adjusted into miles. Due to the fact that the circumference of the planet is roughly 25,000 miles, the size of each level of latitude is about 69 mile (1/360 the 25,000 miles). Levels of latitude vary a tiny in length—the variation between the shortest and the longest is much less than a mile—because the planet is no a perfect sphere but is planarization slightly towards the poles and also bulges slightly roughly the equator. The length of a level of longitude, however, varies from around 69 miles at the equator to zero at the poles, wherein the meridians come together.

Finding Latitude and also Longitude

The navigator the a ship or an airplane can determine latitude by using an instrument dubbed a sextant. Through it the navigator measures the altitude (angle above the horizon) that the sunlight as the sun transits, or crosses, the meridian (longitude).

The navigator then calculates the latitude by combining the it was observed altitude with information from one almanac—a book of data about the movement of the Sun and also stars. In the evening, latitude may similarly be uncovered by observing stars (see navigation).

Longitude is more complicated to determine than latitude since the sextant and the almanac together do not yield sufficient information. To calculate longitude, a navigator must additionally know the specific time at which the observations are made. The time is needed due to the fact that the Sun and stars, as they show up to move across the sky, watch the same at all areas in a offered latitude at part time during each day.

The creation of clocks during the Renaissance was the very first step towards the trustworthy calculation the longitude. The clocks of the era, however, were as well inaccurate for use in navigation. In 1714 the British board of Longitude readily available a large cash prize to anyone that could construct a clock that would meet specific standards of accuracy throughout lengthy ocean voyages. Through 1735 man Harrison, a brothers clockmaker, had submitted the an initial of numerous clocks, the critical of which winner the prize for him. Lock were referred to as chronometers. In 1766 Pierre Le Roy, a Frenchman, constructed a chronometer much more accurate than Harrison’s. From that time on, sailors have been maybe to determine longitude that s right by comparing regional time through Greenwich median time (GMT). (See also time.)

Shipboard chronometers are set to display GMT. Because of the speed and also direction of the earth’s rotation, local time in ~ a given place will certainly be one hour behind GMT for every 15 levels west that the element meridian and one hour ahead of GMT for every 15 degrees east that the element meridian. Because that example, if a ship’s chronometer reads 0300 (3:00 am) and also the ship’s local time is 0800 (8:00 am), the delivery is 75 degrees east of Greenwich, or in ~ 75° E. Special radio time signals enable navigators to check the accuracy of their chronometers.

How the prime Meridian to be Selected

Before a prime meridian to be agreed upon, map devices usually began numbering the present of longitude on your maps in ~ whichever meridian passed v the website of their national observatory. In the united States, for example, this was the naval Observatory in ~ Washington, D.C.; in France, the Paris Observatory; and also in an excellent Britain, the royal Greenwich Observatory, in ~ Greenwich.

Since Britain was a people leader in exploration and map making, navigators of various other nations regularly used british maps. Together a result, in 1884 the meridian the Greenwich was adopted throughout many of the human being as the element meridian. In the 1950s the royal Greenwich Observatory was moved around 60 mile southeast the Greenwich. The Greenwich meridian, however, stayed the prime meridian.

There to be still one more reason for the an option of the Greenwich meridian as 0° longitude. Travelers must change time by whole day once they overcome the 180th meridian. If this meridian overcome a huge country, timekeeping and also the facility of calendar dates would be difficult. However with the Greenwich meridian set at zero, the 180th meridian is near the center of the Pacific Ocean. The crosses only a small land area in northeastern Asia and divides some island teams in the Pacific.

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To stop differing dates in those areas, the nations of the civilization established a unique line throughout which dates change. That swerves indigenous the 180th meridian whenever convenient. This heat is referred to as the international date line.