The earth rotates from west to east over its axis. It makes the sun rise in the east and set in the west. 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 15° of longitudes per hour or one degree of longitude in every four minutes of time. The time decreases when we move from west to east and increases with our westward movement. The rate of the time at which the sun traverses over certain degrees of longitudes is used to determine the local time of an area with respect to the time at the Prime Meridian (0°Longitude). For example when it is 2 pm in Greenwich, it will be 3 pm in 15° east. (15 × 4 = 60 minutes = 1 hour).
