Longitude and Time
We are all aware that the Earth rotates from west to east on its axis, causing the sun to rise in the east and set in the west. This rotation takes approximately 24 hours to complete a full circle or 360° of longitudes. Since there are 180° of longitudes both east and west of the Prime Meridian, the sun requires 12 hours to traverse each hemisphere. Therefore, the sun moves across 150° of longitudes per hour or one degree of longitude every four minutes.
The rate at which the sun moves over specific degrees of longitudes is utilized to determine the local time of an area relative to the time at the Prime Meridian (0° Longitude). To illustrate this concept, let’s consider the following examples:
Example 1: Determining the local time of Thimphu (Bhutan) situated at 90° east longitude when the time at Greenwich (0°) is 12:00 noon. Solution: Since the time increases by 4 minutes for every degree of longitude east of the Prime Meridian, the total time difference for Thimphu is 6 hours. Therefore, the local time of Thimphu is 6:00 p.m.
Example 2: Determining the local time of New Orleans (the location severely affected by Hurricane Katrina in October 2005) situated at 90° west longitude when the time at Greenwich (0°) is 12:00 noon. Solution: Since the time decreases by 4 minutes for every degree of longitude west of the Prime Meridian, the total time difference for New Orleans is also 6 hours. Thus, the local time of New Orleans is 6:00 a.m.
Similarly, this method can be applied to determine the time for any location worldwide. However, to maintain uniformity of time within a country, the standard time at the central meridian of the country is adopted as the Standard Time for the entire nation. The Indian Standard Time (IST) is calculated from the 82°30’E meridian passing through Mirzapur. Therefore, IST is 5 hours 30 minutes ahead of GMT. Other countries around the world also establish their standard meridians within their territories to determine time zones within their administrative boundaries, especially in countries with significant east-west spans like Russia, Canada, and the United States of America. The world is divided into 24 major time zones, each covering 15° of longitude.
Latitude, Longitude and Time| Class 11 Geography Practical Work
The geographic coordinate system, consisting of latitude and longitude, is essential for locating and identifying positions on the Earth’s surface. This system, along with the concept of time zones, allows for the standardization of time and the organization of global activities.
Let us learn more about the latitude, longitude, and time!
Latitude, Longitude and Time| Class 11 Geography Practical Work
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