Latitude, Longitude, and Time

Introduction

• The Earth is not a perfect sphere but an oblate spheroid due to equatorial bulging.
• To locate places, a network of imaginary lines is drawn, forming the geographical grid.
• The grid consists of parallels of latitude (horizontal lines) and meridians of longitude (vertical lines).

Parallels of Latitude

• Definition: The angular distance of a point north or south of the Equator.
• The Equator is 0° latitude, dividing the Earth into Northern and Southern Hemispheres.
• Poles are at 90° N (North Pole) and 90° S (South Pole).
• Latitudes are measured in degrees (°), minutes (‘), and seconds (“).
• Total Parallels: 179 (including Equator).
• Major Latitudes:
  • 0° – Equator
  • 23.5° N – Tropic of Cancer
  • 23.5° S – Tropic of Capricorn
  • 66.5° N – Arctic Circle
  • 66.5° S – Antarctic Circle
  • 90° N – North Pole, 90° S – South Pole
• Distance between latitudes: ~111 km per degree.

Meridians of Longitude

• Definition: The angular distance east or west of the Prime Meridian (0°).
• Unlike latitude, all longitudes are equal in length.
• Prime Meridian (0°) passes through Greenwich, London.
• Range: 0° to 180° east and west.
• Longitude helps in determining time zones.
• Distance between longitudes varies:
  • 111.3 km at the Equator
  • 79 km at 45° latitude
  • 0 km at the poles (converging points)

Longitude and Time

• The Earth rotates 360° in 24 hours, moving 15° per hour.
• Each degree of longitude accounts for 4 minutes of time difference.
• Eastward movement = Time increases (+4 min per degree).
• Westward movement = Time decreases (-4 min per degree).

Example Calculations:

• If GMT (Greenwich Mean Time) is 12:00 noon:
  • Thimpu (90° E) → Local Time = 6:00 PM
  • New Orleans (90° W) → Local Time = 6:00 AM

Standard Time and Time Zones

• Each country adopts a Standard Meridian for uniform timekeeping.
• Indian Standard Time (IST):
  • 82°30′ E (Mirzapur, Uttar Pradesh).
  • IST is GMT +5:30 hours.
• Countries with large east-west spans have multiple time zones (e.g., USA, Russia, Canada).
• Total time zones worldwide: 24.

International Date Line (IDL)

• Located at 180° longitude (opposite the Prime Meridian).
• Separates different calendar dates.
• Eastward crossing → +1 day.
• Westward crossing → -1 day.
• Not a straight line; zigzags to accommodate political and national borders.

Key Differences Between Latitude and Longitude

Source: NCERT