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

The Earth is approximately spherical, although it’s not a perfect sphere due to differences in its equatorial and polar radii. Rotation on its axis causes bulging at the equator, giving it the shape of an oblate spheroid. This shape poses challenges in positioning surface features, so a network of imaginary lines is used to locate points.

The geographical grid is based on the North and South Poles, which serve as natural reference points. It consists of two sets of intersecting lines: parallels of latitude and meridians of longitude.

Parallels of latitude are horizontal lines drawn parallel to the equator, dividing the Earth into two unequal halves. The equator, the largest circle, divides it into equal halves, while other parallels decrease in size toward the poles. These lines are referred to as parallels of latitude.

Meridians of longitude are vertical lines joining the poles. They are farthest apart at the equator and converge at the poles. Together with parallels of latitude, they form a systematic network of lines, known as geographical coordinates, used to represent the positions of Earth’s surface features.

Geographical coordinates, represented by latitudes and longitudes, facilitate determining the location, distance, and direction of various points on Earth’s surface. While an infinite number of parallels and meridians can be drawn, maps typically display a selected number of them. These coordinates are measured in degrees, minutes, and seconds, providing angular distances for accurate positioning.

Parallels of Latitudes

1. Definition of Latitude: Latitude is the north-south position of a point on the Earth’s surface. It is measured in degrees north or south of the Equator, the imaginary line dividing the Earth into the Northern and Southern Hemispheres.

2. Heat Zones: The Earth is divided into different heat zones based on latitude. These include the Torrid Zone (near the Equator), the Temperate Zones (between the Tropics and the Arctic/Antarctic Circles), and the Frigid Zones (near the North and South Poles).

3. Parallels of Latitude: Parallels of latitude are the imaginary east-west lines that run parallel to the Equator. They are used to measure the position of a location north or south of the Equator.

Drawing the Parallels of Latitudes

To draw parallels of latitude, begin by drawing a circle representing the Earth’s surface. Divide the circle into two equal halves with a horizontal line to indicate the equator. Position a protractor on the circle so that the 0° and 180° lines align with the equator on the paper.

Next, to draw a parallel such as 20°S, mark two points on the lower half of the circle at an angle of 20° from the equator, one east and one west, as demonstrated in Figure 3.2. The arms of this angle will intersect the circle at two points.

Connect these two points by drawing a line parallel to the equator. This line represents the parallel of latitude at 20°S. Repeat this process for drawing other parallels of latitude as needed.

Meridians of Longitude

1. Definition of Longitude: Longitude is the east-west position of a point on the Earth’s surface. It is measured in degrees east or west of the Prime Meridian, an imaginary line that passes through Greenwich, England.

2. Meridians of Longitude: Meridians of longitude are the imaginary north-south lines that run from the North Pole to the South Pole. They are used to measure the position of a location east or west of the Prime Meridian.

3. Prime Meridian: The Prime Meridian is the line of longitude that passes through Greenwich, England, and is used as the starting point for measuring longitude.

4. International Date Line: The International Date Line is an imaginary line in the Pacific Ocean that marks where the date changes by one day. It is roughly opposite the Prime Meridian.

Drawing the Meridians of Longitude

To draw lines of longitude, start by drawing a circle representing the Earth’s surface with its center indicating the North Pole. The circumference of the circle corresponds to the equator. Draw a vertical line through the center of the circle, intersecting the North Pole. This line represents the 0° and 180° meridians, which converge at the North Pole, as illustrated in Figure 3.4.

When observing a map, typically, east is on the right and west is on the left. However, to draw longitudes, imagine yourself at the North Pole, positioned at the center of the circle depicted in Figure 3.4. From this perspective, the directions of east and west would be reversed, with east to your left and west to your right.

To draw a specific longitude, such as 45° E and W, envision yourself at the North Pole, and place your protractor along the vertical line, aligning it with the 0° and 180° meridians. Then, measure 45° on both sides of the vertical line, denoting 45° E meridian to your left and 45° W meridian to your right, as shown in Figure 3.5.

This diagram represents the Earth’s appearance when viewed directly from above the North Pole.

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.

Parallels of Latitude vs Meridians of Longitude

S. No.	Parallels of Latitude	Meridians of Longitude
1.	Latitude is the angular distance of a point north or south of the equator, measured in degrees.	Longitude is the angular distance along the equator measured in degrees. It is measured east or west of Greenwich (0°), from 0° to 180°.
2.	All latitudes are parallel to the equator.	All meridians of longitude converge at the poles.
3.	On a globe, parallels of latitudes appear as circles.	All meridians of longitude appear as circles running through the poles.
4.	The distance between two latitudes is approximately 111 km. Maximum at the equator (111.3 km) and minimum at the poles (0 km). Midway, at 45° of latitude, it is 79 km.	The distance between two longitudes varies. It is maximum at the equator and decreases towards the poles.
5.	The 0° latitude is referred to as the equator, and the 90° latitude as the poles.	There are 360° of longitude, 180° each in the east and west of the Prime Meridian.
6.	The latitudes from the equator to the poles are used to demarcate temperature zones: 0° to 23 ½° north and south as the torrid zone, 23 ½° to 66 ½° as the temperate zone, and 66 ½° to 90° as the frigid zone.	The longitudes are used to determine local time with reference to the time at the Prime Meridian.

International Date Line

The world is divided into 24 time zones, but there needs to be a designated place where the day officially changes on the planet. This place is approximately along the 180° line of longitude, known as the International Date Line. At this longitude, the time is exactly 12 hours ahead or behind the time at the Prime Meridian (0° longitude), regardless of whether one travels eastward or westward.

For someone traveling eastward from the Prime Meridian, the time would be 12 hours less than at 0° longitude, while for someone traveling westward, the time would be 12 hours more. For instance, if a person moves eastward and crosses the International Date Line on a Tuesday, they would consider it Wednesday. Conversely, someone starting their journey on the same Tuesday but traveling westward would consider it Monday once they cross the line.

Conclusion

The understanding of latitude, longitude, and time is crucial for navigation, communication, and the coordination of global operations. This knowledge underpins many aspects of modern life and continues to be an important foundation for geographical and scientific inquiry.

Latitude, Longitude and Time- FAQs

What is latitude?

Latitude is the north-south position of a point on the Earth’s surface, measured in degrees north or south of the Equator.

What are the heat zones based on latitude?

The Earth is divided into the Torrid Zone (near the Equator), the Temperate Zones (between the Tropics and the Arctic/Antarctic Circles), and the Frigid Zones (near the North and South Poles).

What is longitude?

Longitude is the east-west position of a point on the Earth’s surface, measured in degrees east or west of the Prime Meridian.

What is the Prime Meridian?

The Prime Meridian is the line of longitude that passes through Greenwich, England and is used as the starting point for measuring longitude.

Why do we need standard time?

Standard time is necessary to coordinate activities, transportation, and communication across different locations, as it ensures consistency within a region.