Earth is the home of all living things. Life is possible on it because it has air and water. Thousands of years ago, man believed that the Earth was flat and surrounded by sea. The sailors in those days did not go far from the coast, They were afraid of falling off the edge of the flat Earth. Today, there is no doubt about the shape of the Earth. It is spherical like a ball. The photographs taken from the spaceships have confirmed this.
More than seventy per cent of the Earth’s surface is covered with water, The large water bodies are called the oceans, while the large landmasses are called the continents. The surface of the landmasses is not smooth. It has plains, plateaus and mountains. The bottom of the oceans and seas is covered with silt and mud. On the ocean floor too there are plains, plateaus, valleys and mountains.
But it is not possible to see the whole Earth at a time. So man made a model of the Earth, A globe is a man-made model of the Earth showing the continents, countries, oceans and rivers in their correct shape and positions. Find the names of the oceans and continents with the help of a globe.
Look at the globe and locate the two end points. The one at the top is called the North Pole, while the one at the bottom is called the South Pole, The line joining these two end points is called the axis of the Earth.
It is an imaginary line. The Earth rotates on its axis from west to east. It is the rotation of the Earth on its axis which causes day and night.
If you look at the globe carefully you will see lines running from the North Pole to the South Pole. These are called meridians of longitude. You will see another set of parallel lines running horizontally in circles. These are called parallels of latitude.
Parallels of Latitude :
The Equator is the largest and most important line of latitude. It runs around the globe, mid-way between the two poles. It divides the globe into two equal parts—the Northern Hemisphere and the Southern Hemisphere. All other latitudes are parallel to the Equator. All the latitudes in the Northern Hemisphere are called ‘north latitudes’ and those in the Southern Hemisphere are called ‘south latitudes’. Whenever we mention a latitude, we must follow it by ‘N’ or 4S’ to show if it is north or south of the Equator.
Some lines of latitude are given special names.
1. The Equator which is at 00.
2. The Tropic of Cancer, which is at an angle of 23]/20 to the Equator, lies in the Northern Hemisphere.
3. The Tropic of Capricorn, also at an angle of 23]/20 to the Equator, is in the Southern Hemisphere.
A. The Arctic Circle is situated at 66Jfc°N and 5, The Antarctic Circle is situated at 66V2°S.
These lines of latitude are important because they help us in dividing the Earth into different heat zones.
The Lines of Longitude :
These semi-circular imaginary lines are drawn from the North Pole to the South Pole, The distance between each line is greatest at the Equator and keeps decreasing away from it till they meet at the Poles. The distance between the longitudes is measured in degrees. Each degree is further divided into minutes and seconds.
There are a total of 360 meridians. But as all longitudes are of the same length, the Meridian of Greenwich was chosen in 1884 by the nations of the world as the Prime or Chief Meridian. It is marked as 0°. The other meridians are marked from 0° to 180° East or West of the Prime Meridian. The lines of 0° and 180° join to form a full circle which divides the Earth into the Eastern and Western Hemispheres.
Location places on a map :
When we are on land we can locate the position of a place with respect to some landmarks or some prominent places.
But at sea, there are no such landmarks. It is difficult to know whether we are near land or far away from it. For this and for many other reasons, we need the Parallels and Meridians which help us find the exact location of a place. These two sets of lines intersect at right angle, resulting in the formation of a network, called grid. The grid helps us locate places on the globe1 or on the map.
Suppose, we want to find the location of Delhi on the map. The latitude of Delhi is about 28°N and the longitude is about 77°E. Delhi will be found at the point where the Parallel of 28°N and the Meridian of 77°E intersect.
This method helps us locate any place on the globe or on the map.
Earth is the home of all living things.
Life is possible on Earth because it has air and water.
More than seventy per cent of the Earth’s surface is covered with water.
A globe is a man-made model of the Earth.
The Earth is spherical in shape like a ball.
Lines running from the North Pole to the South Pole are called meridians of longitude.
Parallel lines running horizontally are called parallels of latitude.
The Equator divides the Earth into two hemispheres.
The Parallels are full circles, but not equal in length.
The Meridians are semicircles, equal in length.
The network of Parallels and Meridians is called the grid.
The grid helps us in locating places on the map.