NCERT Class 11 Geography Practical Chapter 3: Longitude, Latitude and Time

Earth is Oblate Spheroid or Geiod

• Equatorial radius and the polar radius of the earth is not the same
• Rotation on axis produces bulge at equator
• network of imaginary lines is drawn on a globe or a map to locate various places – geographical grid
• The grid consists of two sets of horizontal and vertical lines, which are called parallels of latitudes and the meridians of longitudes

Latitude or Parallel – Drawing Them

• Horizontal lines parallel to each other and appear as circles
• Angular distance, in degrees, minutes and seconds of a point north or south of the Equator
• Midway between north & south pole is equator
• Divide globe in 2 equal half – great circle
• Rest are smaller – called parallels or latitude
• If parallels of latitude are drawn at an interval of one degree, there will be 89 parallels in the northern and the southern hemispheres each. The total number of parallels thus drawn, including the equator, will be 179.
• If earth was perfect sphere – length of one degree would be 111 km and would be same as longitude.
• But the degree of latitude changes slightly in length from the equator to the poles. While at the equator, it is 110.6 km at the poles, it is 111.7 km.
• Latitude of a place may be determined with the help of the altitude of the sun or the Pole Star.
• Draw Parallels: Draw a circle and divide it into two equal halves by drawing a horizontal line in the center. This represents the equator. Place a protractor on this circle in a way that 0° and 180° line on the protractor coincide with the equator on the paper. Now to draw 20°S, mark two points at an angle of 20° from the equator, east and west in the lower half of the circle. The arms of the angle cut the circle at two points. Join these two points by a line parallel to the equator. It will be 20⁰S.

Longitude or Meridian – Drawing Them

• Run N-S
• Join the poles
• Called meridians
• Angular distance, in degrees, minutes, and seconds, of a point east or west of the Prime (Greenwich) Meridian
• Farthest at equator and converge at poles
• Help in coordinates, location, distance and direction
• Infinite number of these can be drawn – but we draw selected ones
• Latitudes and longitudes are measured in degrees (°) because they represent angular distances. Each degree is further divided into 60 minutes ( ′ ) and each minute into 60 seconds ( ″ ) .
• Unlike the parallels of latitude which are circles, the meridians of longitude are semi-circles that converge at the poles – (if opposite are taken, they complete circle and are valued as 2 meridians)
• The meridians intersect the equator at right angles
• Greenwich is zero-degree meridian passing through London
• The longitude of a place is its angular distance east or west of the Prime Meridian. It is also measured in degrees.
• The rotation of the earth over its axis takes 24 hours to complete one circle or 360° of longitudes. As 180° of longitudes fall both east and west of the Prime Meridian, the sun, thus takes 12 hours՚ time to traverse the eastern and western hemispheres. In other words, the sun traverses 150 of longitudes per hour or one degree of longitude in every four minutes of time
• Distance b/w 2 longitude is maximum at equator 111.3 km and at 45 degrees it is 79 km, converging at poles.
• Determine local time

Solving Problems on Latitude & Longitude

• Determine the local time of Thimpu (Bhutan) located at 90° east longitude when the time at Greenwich (0°) is 12.00 noon.
• Difference between Greenwich and Thimpu = 90° of longitudes
• Total Time difference = 90 x 4 = 360 minutes
• = 360/60 hours
• = 6 hours or Local time of Thimpu is 6 hours more than that at Greenwich, i.e.. 6.00 p. m.
• If the location is 90° west of Greenwich it would be 6 hours behind. We take standard time to maintain uniformity across country
• The Indian Standard Time is calculated from 82°30 ′ E meridian passing through Mirzapur. Therefore, IST is plus 5.30 hours from the GMT
• The world is divided into 24 major time zones

International Date Line

• The 180° line of longitude is approximately where the International Date Line passes
• The time at this longitude is exactly 12 hours from the 0-degree longitude, irrespective of one travels westward or eastward from the Prime Meridian
• Cross eastward <- it is loss a day from Thursday to Friday
• Crossing westward -◊ it is gaining a day Thursday to Wednesday.