Latitude and Longitude
A (geographical) meridian (or line of longitude) is the half of an imaginary great circle on the Earth's surface, terminated by the North Pole and the South Pole, connecting points of equal longitude, as measured in angular degrees east or west of the Prime Meridian. . Therefore, a compass needle will be parallel to the magnetic meridian. Meridians (lines of longitude) and parallels (lines of latitude) intersect at right angles. distances from the center of the projection to any other place on the map. Shape and scale distortions increase near points 90 degrees from the central line. Has straight meridians and parallels that meet at right angles, but straight. These lines are called parallels of latitude and meridians of longitude. and from the north pole (or south pole) forms a right angle, which is 90°. East and west longitude meet at the ˚ meridian, which runs through the Pacific ocean basin ( Fig. To locate a point on a globe exactly, degrees of latitude and longitude are .
Where the 90th east-west lines would be are two points—the North and South poles. Each east-west line is a circle. The farther it is from the equator the shorter its length. The 60th east-west line, for example, is only half as long as the equator. East-west lines are numbered from 0 at the equator—the east-west base line—to 89 near the poles. The east-west lines between the equator and the North Pole are north of the equator; those between the equator and the South Pole, south of the equator.
The city of New Orleans, Louisiana, is located on the 30th east-west line north of the equator. But many other places in the world are also situated on this line. That is why a second set of lines is needed to locate the exact position of New Orleans—or of any other place.
Latitude and longitude
These are north-south lines, or lines of longitude. One north-south line has been chosen by international agreement as the zero, or base line. It passes through Greenwich, England, a borough of London. In the basic grid there are such equally spaced lines to the east of the Greenwich base line, to the west. Unlike east-west lines, all north-south lines have the same length. North-south lines are numbered from 0 at the north-south base line both east and west to the th north-south line.
The zero line and the th line together form a complete circle that, like the equator, cuts the Earth into two hemispheres. The half west of the zero line can be called the Western Hemisphere; the half east of the zero line, the Eastern Hemisphere.
The north-south lines and the east-west lines together form the global grid system used to find the exact location of any place on Earth. New Orleans, on the 30th east-west line north of the equator, is also on the 90th north-south line west of the north-south base line.
Many places in the world—among them, Memphis, Tennessee; East St. Many other places—for example, Port Arthur, Texas; St. But only New Orleans is situated on both lines—exactly where they cross each other. Likewise, each place in the world—and only that place—is situated at the intersection of a given east-west line and a given north-south line.
Parallels and Meridians All east-west lines are equidistant from each other. This means that they are all parallel to the equator and to each other.
Every point on a given east-west line, therefore, is the same distance from the equator, the same distance from the North Pole, and the same distance from the South Pole. For this reason east-west lines, or lines of latitude, are commonly referred to as parallels of latitude, or simply parallels.
Are all parallels and meridians meet at angles other than 90 degrees
The north-south lines, or lines of longitude, also have another name. They are commonly referred to as meridians of longitude, or simply meridians. The zero meridian, or base line for numbering the north-south lines, is called the prime meridian. Each meridian goes only halfway around the Earth—from pole to pole.
Each has a twin on the other side of the Earth. Like the prime meridian and the th meridian, all such pairs of meridians form circles that cut the Earth into hemispheres. These circles are known as great circles. Only one parallel, the equator, is a great circle. A cutaway drawing of the Earth demonstrates how latitude is determined.
It makes clear that latitude is a measure of the angle between the plane of the equator and lines projected from the center of the Earth. The cutaway drawing of the Earth also shows how longitude is determined. Longitude is seen to be a measure of the angle between the planes of two meridian circles, one of which is the prime meridian.
Any location on Earth can be described as lying at a certain number of degrees and minutes of latitude either north or south of the equator and at a certain number of degrees and minutes of longitude either east or west of the prime meridian. A degree of latitude can easily be changed into miles.
Degrees of latitude vary a little in length—the variation between the shortest and the longest is less than a mile—because the Earth is not a perfect sphere but is flattened slightly toward the poles and bulges slightly around the equator. The length of a degree of longitude, however, varies from about 69 miles at the equator to zero at the poles, where the meridians come together. Finding Latitude and Longitude The navigator of a ship or an airplane can determine latitude by using an instrument called a sextant.
With it the navigator measures the altitude angle above the horizon of the Sun as the Sun transits, or crosses, the meridian longitude.
latitude and longitude
The navigator then calculates the latitude by combining the observed altitude with information from an almanac—a book of data about the movement of the Sun and stars. In the evening, latitude may similarly be found by observing stars see navigation. Longitude is more difficult to determine than latitude because the sextant and the almanac together do not yield enough information. To calculate longitude, a navigator must also know the exact time at which the observations are made.
The time is needed because the Sun and stars, as they appear to move across the sky, look the same at all places in a given latitude at some time during each day. The invention of clocks during the Renaissance was the first step toward the reliable calculation of longitude.
The clocks of that era, however, were too inaccurate for use in navigation. In the British Board of Longitude offered a large cash prize to anyone who could build a clock that would meet certain standards of accuracy throughout long ocean voyages.
By John Harrisona British clockmaker, had submitted the first of several clocks, the last of which won the prize for him. The prefix hemi- means "half"; thus, hemisphere means "half-sphere. Movement toward the North Pole is northerly in direction. Movement toward the South Pole is southerly in direction. Degrees of latitude are measured from an imaginary point at the center of the earth. If the earth was cut in half, this imaginary point would be intersected by a line drawn from the North Pole to the South Pole and by a line drawn from the equator on one side of the earth to the equator on the other Fig.
A radius is a line drawn from the edge of a circle to its center. To calculate the angle, draw a line from the point to the center of the earth and a line from the equator to the center of the earth Fig.
Parallels of latitude are imaginary reference lines that form complete circles around the earth parallel to the equator and parallel to each other.
Every point on a parallel of latitude is the same distance from the equator, and thus the angle formed between the equator and the latitude line is constant. This is shown in Fig. Parallels of latitude are circles of different sizes see Fig. The largest parallel is at the equator, and the parallels decrease in size towards the poles.