Horizontal lines drawn on a globe or a map are called lines of latitude. Since these lines run parallel to each other they are called parallels of latitudes. The latitude of a place on the Earth’s surface is its angular distance in the north or in the south of the equator. It is measured as an angle subtended at the centre of the earth. The latitudes are always expressed in degrees. They are numbered from 0° to 90° North and South. Equator is located at 0°. Each degree of latitude is divided into 60 minutes and a minute is further sub-divided into 60 seconds. Suppose the latitude of a place is 8 degrees 4 minutes and 25 seconds, we can express it as 8°, 4’, 25. The lines of latitude are the imaginary lines which encircle the earth. All of them are parallel to the equator. All places having the same value of latitude to the north or the south of the equator lie on the same latitude. For example, 30° N latitude line joins all places situated at an angular distance of 30° north of the equator. The equator, being in the middle of the two poles of the earth is the longest line of latitude.Its length is equal to the circumference of the earth which is about 40,075.16 km.
As we move away from the equator, the circumference of the circle decreases. The two poles are, however, only points. While writing the parallels of latitudes, it is essential to write letter N or S with them. Letter ‘N’ is written with the latitudes of the Northern Hemisphere and ‘S’ with the latitudes of the Southern Hemisphere. For example, Kerala (in India) is situated between 8°18’N to 12°48’N of equator. The number of latitudes, when drawn at 1° interval, are 90 in the Northern Hemisphere and 90 in the Southern Hemisphere. The latitude of the Equator is 0°. Besides the equator and two poles, other important lines of latitude are: 1. The Tropic of Cancer (231⁄2° N) - It lies north of the equator in the Northen Hemisphere. 2. The Tropic of Capricorn (231⁄2° S) - It is located south of the equator in the Southern Hemisphere. 3. The Arctic Circle (661⁄2° N) - This important line of latitude is above the Tropic of Cancer in the Northern Hemisphere. 4. The Antarctic Circle (661⁄2° S) - It is below the Tropic of Capricorn in the Southern Hemisphere.
Parallels of latitude
The meridians of longitude are a set of imaginary vertical lines. They are in the form of semi¬circles which converge towards the two poles and are the widest at the equator. Unlike the parallels of latitudes, they are all equal in length. The lines of longitudes are drawn all around the globe at an interval of an angle of 1°. As all these lines of longitudes are equal, one particular line of longitude was to be selected for numbering them. The line of longitude passing through the British Royal Observatory at Greenwich, London, has been adopted as the Prime Meridian or 0° Longitude. There are 180° longitudes each drawn on both sides of the Prime Meridian. The value of the meridians of longitude starts from 1° to 180° towards the east as well as towards the west side of the Prime Meridian. The half part of the earth on the east to the Prime Meridian is called Eastern Hemisphere and the other half to the west is called the Western Hemisphere. Thus, in each hemisphere there are 180 longitudes. The total number of longitudes is, thus, 360. Meridians to the east of Prime Meridian are marked as ‘E’, whereas to the west of Prime Meridian as ‘W’. However, 180° is a common line and form International date line in the Pacific Ocean
Some parts of the earth receive more heat than other parts because of the variation in the angle of the rays of the sun. Depending on the heat received, the zones are named differently. These are-Torrid Zone, Temperate Zone and Frigid Zone. Let us discuss them one by one
THE TORRID ZONE
The Tropic of Cancer and the Tropic of Capricorn mark the limits of this zone. In this zone, the rays of the sun are exactly overhead once a year except on the equator, where the mid-day sun is overhead twice a year. Hence, it receives maximum heat from the sun and is very hot.
THE TEMPRATE ZONE
The zone between the Tropic of Cancer and the Arctic Circle is called the North Temperate Zone. The zone between the Tropic of Capricorn and the Antarctic Circle is called the South Temperate Zone. The sun rays in both these zones are never directly overhead. The angle of the sun rays decreases as we go towards the poles. That is way these zones are neither very hot nor very cold. They have moderate temperature.
THE FRIGID ZONE
It lies from Arctic Circle to the North Pole and from Antarctic Circle to the South Pole. This zone remains covered with ice and snow for the most part of the year because the rays of the sun are always slanting. Hence, it is the coldest zone of the earth.