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Longitudes

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Longitudes - Lesson Summary

The imaginary lines running from the North Pole to the South Pole on the globe are called longitudes. An English clockmaker, John Harrison, devised the concept of longitudes. Knowing the latitude and the longitude of a place, we can determine the location of that place on the globe accurately.

If you plot the lines of latitude and longitude on a map, you get a grid pattern. This is called the Earth grid, or Graticule. Longitudes are also known as meridians. 

The word ‘meridian’ means mid-day. All the places situated on a particular longitude have their noon at the same time. Therefore, they are called meridians of longitude.
 
Characteristics of longitudes:
  • Distances between longitudes are measured in ‘degrees of longitude.’
  • Each degree is further divided into minutes, and minutes into seconds.
  • Longitudes are semi-circular in shape.
  • The distance between longitudes reduces as they move towards the poles.

At the poles, the distance between the longitudes is zero. It is shortest at the poles where all the meridians meet. The distance at the poles is zero km.
  • All longitudes are of equal length
  • The 0° longitude passes through Greenwich and is called the Prime Meridian
  • The Prime Meridian divides the earth into the eastern hemisphere and the western hemisphere
  • The longitude of a place is followed by the letter E or W. This letter denotes whether the longitude is east or west of the Prime Meridian
  • 180°East meridian and 180° West meridian are the same.

If you cross the 180˚ longitude, the calendar date changes. The imaginary line on the Earth that separates two consecutive calendar days is called the International Date Line.

To avoid having two different dates in the same country, the International Date Line has been made to bend at several places. A great circle bisects the earth into two equal hemispheres. A great circle is the shortest distance between any two points on the globe.

Differences between longitudes and latitudes:
  • Latitudes are horizontal lines on the globe that run west to east, whereas longitudes are vertical lines that run north to south.
  • Latitude lines run parallel to the equator and to each other and measure the distance north or south of the equator while Longitude lines, are neither parallel to each other nor to the Prime Meridian and measure the distance east and west of the Prime Meridian.
  • Values of latitude range from 0° at the equator to 90° N or 90°S at the poles while values of longitude range from zero degrees at the Prime Meridian to 180°E or 180°W.
  • The lines of Latitudes get shorter as we move towards the poles and latitudes become points at the poles while Longitudes, are all of equal length and converge to meet at the poles.

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