Introduction - The Globe
Look at the picture of the earth and observe:
It is spherical, like a ball.
You can see only one-half of it, you cannot see the other half.
Now look at the globe in your class and observe:
It is also spherical.
It is set on a stand at a slight angle.
You can see only one-half of it, you cannot see the other half.
If you want to see the other half, you have to rotate it.
The earth rotates on its axis, so a globe is set on a stand such that it can be rotated.
Main Features of the Earth
The earth’s surface is covered with land or water areas.
The large land areas are called continents. They are seven in number : Asia, Africa, North America, South America, Europe, Australia and Antarctica.
The large water areas are called oceans. They are five in number : Pacific Ocean, Atlantic Ocean, Indian Ocean, Arctic Ocean and Southern Ocean.
Axis, North Pole and South Pole
The enormity of the Earth prohibits a comprehensive study of the entire planet, hence it is divided into segments using imaginary lines drawn on the globe. These lines, which do not exist on Earth’s surface, are created by drawing horizontal and vertical lines. The horizontal lines are known as latitudes, while the vertical lines are commonly referred to as...
Latitudes
Latitudes are horizontal lines. The longest latitude is called the Equator. It is drawn midway between the North Pole and the South Pole. Thus, this line divides the earth into two parts. The part above the Equator is the northern part and is called Northern Hemisphere; and the part below the Equator is the southern part and is called Southern Hemisphere. Some more latitudes are drawn parallel to the Equator. As they are parallel to each other, they never meet as they have equal distance everywhere. They are also called Parallels of Latitude. A total of 90 latitudes are drawn in each hemisphere. Thus, there are 90 latitudes in the Northern Hemisphere and 90 latitudes in the Southern Hemisphere. The latitudes in the Northern Hemisphere are called North Latitudes, and those in the Southern Hemisphere are called South Latitudes.
All latitudes are marked in degrees. The Equator is marked 0°. The smallest latitudes are North Pole and South Pole, and both of them are marked 90°.
Latitudes in the Northern Hemisphere are designated with the label ‘N’, while those in the Southern Hemisphere are designated with the label ‘S’. To illustrate, a latitude of 45° in the Northern Hemisphere would be written as 45°N, while the same latitude in the Southern Hemisphere would be 45°S. The North Pole is identified as 90°N and the South Pole as 90°S.
The latitudes which are near the Equator are called low latitudes and those near the poles are called high altitudes.
Important Latitudes
The Equator is the most important latitude and is marked 0°. It divides the globe into two equal halves. Other important latitudes are the following:
Tropics: The latitudes drawn at 23½°N are called tropics. They are two in number: one in the Northern Hemisphere and the other in the Southern Hemisphere. The Tropic of Cancer lies at 23½°N. The Tropic of Capricorn lies at 23½°S.
Circles: The latitudes at 66½°N are called circles. They are two in number: one in the Northern Hemisphere and the other in the Southern Hemisphere. The Arctic Circle lies at 66½°N. The Antarctic Circle lies at 66½°S.
Poles: We have told you about the two poles. The North Pole lies at 90°N and the South Pole lies at 90°S. They are the smallest latitudes.
Latitudes and Heat Zones
You know that the sun is the source of heat and light on the earth.
Let us do a practical.
Light a candle and place it just in front of the globe. What do you see?
The candle light is brighter in the middle where the light falls direct, and it is not so bright on the sides where the light falls in a slanting manner. It is complete shade on the other side. Now, rotate the globe. You find that the light is shifting to the newer areas and lighted areas are going to the sides and shaded area.
Likewise, the sunlight falls perpendicularly at the Earth’s equator and at an angle towards the sides. Consequently, the regions around the equator experience direct and intense heat, while the poles receive slanted and dispersed sunlight leading to colder temperatures. This classification of temperature variations allows us to divide the Earth into three heat zones:
1. Very Hot Zone: The area around the Equator, within the two tropics (Tropic of Cancer and Tropic of Capricorn) receives direct sunlight. So, it is the hottest area on the earth.
2. Very Cold Zone: The areas around the two poles, within circles, receive very slanting sunlight. So, these are the coldest areas. In other words, the coldest areas on the earth
are located between the North Pole and the Arctic Circle in the Northern Hemisphere and between the South Pole and the Antarctic Circle in the Southern Hemisphere.
3. Moderate Zone : Certain regions receive moderate levels of sunlight, and thus, have a temperate climate that is neither excessively hot nor cold. These regions are located 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.
Longitudes
Latitudes are horizontal lines but longitudes are vertical lines. These lines touch the North Pole on one end and the South Pole on the other end. So, they all are semi-circles. They are also called meridians. All of them are of the same length.
A total of 360 longitudes are drawn and each is marked in degrees, just like latitudes. The longitude passing through Greenwich, an observatory near London, was marked as 0°. This longitude is called the Prime Meridian. This longitude divides the
Earth into two equal halves : Eastern Hemisphere and the Western Hemisphere.
The longitudes are not parallel, so the distance between them is not uniform. They all converge at the poles, and their distance increases towards the Equator. The maximum distance between any two longitudes is at the Equator, where it is about 111 km.
The longitudes lying in the Eastern Hemisphere are marked with ‘E’ and those lying in the Western Hemisphere are marked with “W’. For example, a longitude of 65° in the Eastern Hemisphere is written as 70°E, and in the Western Hemisphere it is written as 65°W.
Longitudes indicate the time, as the Earth’s rotation causes different longitudes to face the sun at different times. The longitude directly preceding the sun is designated as 12 o’clock noon. Moreover, when the sun is directly overhead at your location, it is also 12 o’clock noon at your place.
Grid of Latitudes and Longitudes
When we draw longitudes and latitudes on the globe, they all intersect each other at right angles. This forms a grid. We can locate a place with the help of this grid.