Longitudes and Time Zones

  • The imaginary lines, which run horizontally on the earth’s surface, are called latitudes. Lines of latitude measure north-south position between the poles. The equator is defined as 0 degrees, the North Pole is 90 degrees north, and the South Pole is 90 degrees south.
  • The imaginary lines, which run vertically on the earth’s surface, are called longitudes. Each degree of longitude is sub-divided into 60 minutes, each of which is divided into 60 seconds. The latitudes and longitudes together make the grid system of earth. This grid system is mainly used to locate any place on the earth. The length of a degree of longitude (east-west distance) depends only on the radius of a circle of latitude.
  • The lines running from the North Pole to the South Pole are called the meridians of longitude. There are 360 meridians of longitude. Distance between two meridians is measured in degrees. Each meridian of longitude is a semi-circle. Longitudes converge at the poles and are far apart at the Equator.
  • Every place and country has its own time, influenced by the Sun’s rays and longitudes.
  • The time of a place reckoned by the mid-day Sun is called its local time. Places on the same meridian have same local time.
  • The earth takes 24 hours to complete one rotation on its axis. Therefore, the time taken to traverse one degree of longitude is 4 minutes. Earth rotates from west to east. Hence, 4 minutes is added for each one degree longitude towards east. For each one degree longitude towards west, 4 minutes are subtracted.
  • Local time of a standard meridian is taken as the standard time for whole nation.
  • 82°30’ East longitude has been selected as the ‘standard meridian’ of India, which passes through Mirzapur in Uttar Pradesh.
  • Indian Standard Time is ahead of Greenwich Mean Time by 5 hours and 30 minutes.
  • Time zones are broad strips that measure 15 degrees wide. The world is divided into 24 major time zones.
  • International Date Line is the line at which a day is lost or gained.
  • 12 hours will be added to Greenwich Mean Time if we move eastwards towards the 180 degree longitude from 0 degree.
  • 12 hours will be subtracted from Greenwich Mean Time if we move westwards towards the 180 degree longitude from 0 degree.

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