geo chap 2

• Geographic Grid


  Imaginary lines drawn on the globe to locate places

  
• Latitudes


  Imaginary lines running east to west, parallel to the Equator

  
• Latitudes


  • Used to find location of a place, measure distance from Equator, divide earth into heat zones

  
• Main latitudes


  • Equator (0°)
  • North Pole (90°N)
  • South Pole (90°S)
  • Tropic of Cancer (23.5°N)
  • Tropic of Capricorn (23.5°S)
  • Arctic Circle (66.5°N)
  • Antarctic Circle (66.5°S)

  
• Hemispheres


  Northern and Southern hemispheres divided by the Equator
• Longitudes


  • Used to calculate time differences, divide earth into Eastern and Western hemispheres

  
• Prime Meridian


  Line of longitude at 0° defining the start of longitude measurements

  
• Greenwich Mean Time (GMT)


  Time at the Prime Meridian

  
• International Date Line (IDL)


  180° longitude, opposite the Prime Meridian

  
• Calculating time using longitudes

  1. Each 1° longitude = 4 minutes time difference

  2. East - Gain - Add

  3. West - Lose - Subtract

  
• Only the Equator is a Great Circle, other parallels of latitude are not full circles

  
• EGA-WLS formula


  Used for memorising, where EGA stands for East-Gain-Add and WLS means West-Lose-Subtract. This means that for each 1° longitude towards the East, 4 minutes are to be added and each 1° longitude towards the West, 4 minutes are to be subtracted.
• Longitude


  The angular distance of a place east or west of the Prime Meridian

  
• Longitude


  • All meridians of longitude converge at the poles
  • Individually all lines of longitude are semicircles and of equal length
  • Longitude degrees are measured from the Prime meridian to its east or west
  • The distance between two lines of longitude is maximum at the Equator (111 km) and goes on decreasing towards the poles (0° at the poles)

  
• Local time


  Obtained by the overhead sun at noon. For each degree of longitude, the local time varies by 4 minutes.

  
• Standard Time


  The uniform time based on a central meridian, which must always be divisible by 7.5° to allow time to be reckoned by a unit of half-an-hour

  
• Greenwich Mean Time (GMT)


  The time at Greenwich (0° longitude) has been selected as the mean time, which is used to fix the Time Zones

  
• Indian Standard Time (IST)


  India's central meridian is 82°30'E, which is 5.5 hours ahead of GMT

  
• Calculating time at a place


  Find the longitude of the place

  2. Calculate the time difference from GMT based on the longitude

  3. Add/subtract the time difference from the GMT time to get the local time

  
• International Date Line (IDL)


  The 180° line of longitude, which causes a time difference of a full day on crossing it. When crossing from the east, time will be 12 hours ahead, and when crossing from the west, time will be 12 hours behind.

  
• Locating places on a map/globe


  Identify the latitude and longitude of the place

  2. Find the intersection of the relevant latitude and longitude lines on the map/globe

  
• Great Circle


  A circle that is drawn on the surface of a sphere (such as the earth) that has a radius equal to the radius of the sphere, and whose centre is also the sphere's centre. The Equator is the only latitude that is a great circle, and all longitudes are a part of a great circle.
• Great Circles


  • Infinite number of circles that touch the two opposite ends of the sphere can be drawn on a sphere

  Intersecting great circles always bisect each other
• Small Circles


  Circles which do not pass through the centre of the earth, such as all the parallels of latitudes other than the Equator