Great circles are circles that are drawn on the surface of the Earth in a way that the centre of the Earth also becomes the centre of the circle.
Main characteristics of great circles
- A great circle is the largest circle which can be drawn on the surface of the Earth.
- Many great circles can be drawn on the surface of the Earth.
- All great circles divide the Earth into two hemispheres.
- Intersecting great circles always bisect each other.
- The Equator is the only latitude which is a great circle.
Difference Between Great Circles and Small Circles
| Great Circles | Small Circles |
|---|---|
| The radius of the great circle is equal to the radius of the Earth. | The radii of small circles are smaller than the radius of the Earth. |
| All meridians of longitude are great circles. | All latitudes except the Equator are small circles. |
| All the great circles divide the Earth into halves. | Small circles are circles whose centre point is not the centre of the Earth. |
Uses of Great Circles
- Great circles help in navigation and aviation.
- Navigators use great circles to find the shortest distance between two places on the Earth’s surface.
- Ships crossing the oceans and aircraft flying in the air follow the great circles to save time and fuel.
Limitations of Great Circles
- Aeroplanes are not always able to follow great circles as some countries do not permit them to fly over their country zones.
- At times, great circles may not touch large cities from where the air traffic may originate.
Major Heat Zones of the Earth
Latitudes divide the Earth into three different heat zones. Because the Earth is spherical, different parts of the Earth get heated differently. Based on the heat received from the Sun, the Earth is divided into three heat zones. They are
Torrid Zone: It is a region between the Tropic of Cancer and the Tropic of Capricorn. This region receives the direct vertical rays of the Sun for almost the whole year. Therefore, this zone gets maximum heat from the Sun. This zone is known as the torrid or tropical zone.
Temperate Zone: This zone lies between the Tropic of Cancer and the Arctic Circle in the Northern Hemisphere and between the Tropic of Capricorn and the Antarctic Circle in the Southern Hemisphere. This zone gets the slanting rays of the Sun as the angle of the Sun’s rays goes on decreasing towards the poles. Thus, this zone experiences moderate temperature.
Frigid Zone: The Frigid Zone lies between the Arctic Circle and the North Pole and between the Antarctic Circle and the South Pole. This zone is also known as the polar region. Because it receives the extreme slanting rays of the Sun, the temperature is extremely low throughout the year. This is the reason the polar regions are generally covered with ice.
Northern and Southern Hemispheres
- The Equator divides the Earth into two equal parts. The part lying to the north of the Equator is known as the Northern Hemisphere and the part lying to the south of the Equator is known as the Southern Hemisphere.
- The North Pole (90°N) is located in the Northern Hemisphere at the extreme end of the Earth. The South Pole (90°S) is located to the south of the Equator in the Southern Hemisphere.
- The length of the Equator is equal to the circumference of the Earth which is 40,077 km. Because the Equator is a great circle and the circumference of a circle is equal to 360°, 1° angular distance is approximately equal to 111 km.
- Latitudes help us to find the distance of any place from the Equator based on its degree of latitude. Example: Chennai is located at 13°N. Because 1° latitude = 111 km, the distance of Chennai from the Equator will be 13 × 111 = 1443 km.
Main characteristics of longitudes
- The vertical lines which run from the North Pole to the South Pole are called longitudes or the meridians of longitudes.
- It is not possible to find the exact location of a place only on the basis of latitude. We also have to take into account the longitudes.
- The distance between two longitudes is measured in terms of degrees. Longitudes are semi-circular and the distance between them decreases as they go towards the poles. The distance between two lines of longitude is maximum at the Equator (111 km). The two diametrically opposite lines which make a full circle are also known as a great circle.
- The Prime Meridian is a 0° longitude which passes through the British Royal Observatory in London. It divides the Earth into the Western Hemisphere and the Eastern Hemisphere.
- When the latitudes and longitudes criss-cross each other at right angles, they form a geographical grid or coordinate which helps us to find the exact location of a place.
Also, Read The Earth’s Grid