The earth is round like a ball, and it is impossible to show the whole earth on a flat sheet of paper without distortion. That is why we use a globe – a small model of the earth. The globe shows the shape of the earth, its continents and oceans, and the lines drawn on it help us to locate any place precisely.
On a globe, we see lines drawn from top to bottom and from side to side. These are the lines of latitudes and longitudes. Together they form a network called a grid or the geographic grid, which helps us to find the exact location of any place on the earth.
In this chapter, we will learn about the globe, the equator, the important parallels of latitude, the heat zones of the earth, and the longitudes that help us to calculate time.
A globe is a three-dimensional model of the earth. It is smaller in scale than the earth, but it shows the true shape of the earth and the relative positions of the continents and oceans.
A globe is very useful for studying the earth's shape and the distribution of land and water. However, the globe is not convenient for detailed study because we cannot see the whole of it at one time. Only half of the globe can be seen at a time. For detailed study, we use maps, which are drawings of the earth or parts of it on a flat sheet.
The globe has certain important lines and points: - The earth's axis is an imaginary line passing through its centre, from the North Pole to the South Pole. - The earth rotates on its axis, which is tilted at an angle of 23.5 degrees. - The equator is an imaginary line drawn around the earth, halfway between the North Pole and the South Pole. It divides the earth into two equal halves: the Northern Hemisphere and the Southern Hemisphere.
Latitudes are imaginary lines drawn parallel to the equator, from east to west. They are measured in degrees, from 0 degrees at the equator to 90 degrees at the poles.
The latitude of a place tells us how far it is from the equator, towards the north or the south. Since the earth is a sphere, the parallels of latitude are full circles, but they decrease in size as we move from the equator towards the poles. The latitudes are measured from the equator, so all points on the same latitude are at the same distance from the equator.
There are some important parallels of latitude that we must remember:
These parallels divide the earth into different heat zones, which influence the climate and the lives of the people.
The earth is divided into three main heat zones, based on the amount of sunlight received:
Longitudes are imaginary lines drawn from the North Pole to the South Pole. They are also called meridians. Unlike latitudes, which are parallel circles, longitudes are half-circles that meet at the poles.
Longitudes are measured in degrees from 0 to 180 degrees, both east and west of the Prime Meridian. The Prime Meridian (0 degrees longitude) passes through Greenwich, near London in the United Kingdom. Longitudes help us to calculate time, because the earth rotates on its axis and different longitudes experience sunrise and sunset at different times.
The Prime Meridian (0 degrees longitude) passes through the Royal Observatory at Greenwich. Longitudes are measured east and west of this line, up to 180 degrees.
The earth rotates from west to east, and it takes 24 hours to complete one rotation (360 degrees). So the earth rotates 15 degrees of longitude in one hour. This means that the local time differs by 4 minutes for every 1 degree of longitude. To avoid confusion in time, countries use a standard meridian. The standard meridian of India is 82.5 degrees East, and the time based on it is called the Indian Standard Time (IST), which is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT).
The line of longitude at 180 degrees is called the International Date Line. Crossing this line changes the date by one day.
If we travel from east to west across the International Date Line, we gain a day, and if we travel from west to east, we lose a day. This is because the earth is round, and the calculation of time must be adjusted when we go around the world.
When latitudes and longitudes are drawn together on a globe or a map, they form a grid or a geographic grid. This grid helps us to locate any place precisely.
The location of any place is given by its latitude and longitude, for example, "New Delhi lies at about 28.6 degrees North latitude and 77.2 degrees East longitude". Using the grid, we can find the exact position of any city, country or any point on the earth's surface. This system of locating places is used by sailors, pilots, geographers and travellers all over the world.
| Parallel | Degrees | Position |
|---|---|---|
| Equator | 0 degrees | Divides earth into two hemispheres |
| Tropic of Cancer | 23.5 degrees N | In the Northern Hemisphere |
| Tropic of Capricorn | 23.5 degrees S | In the Southern Hemisphere |
| Arctic Circle | 66.5 degrees N | Near the North Pole |
| Antarctic Circle | 66.5 degrees S | Near the South Pole |
| Zone | Location | Climate |
|---|---|---|
| Torrid Zone | Between the Tropics of Cancer and Capricorn | Hottest, direct sunlight |
| Temperate Zones | Between the tropics and the Arctic/Antarctic circles | Moderate temperatures |
| Frigid Zones | Within the Arctic and Antarctic circles | Very cold, little sunlight |
The globe is a model of the earth that shows us the true shape of our planet and the lines of latitudes and longitudes drawn on it. Latitudes are parallel circles that run east-west, and the important parallels divide the earth into the Torrid, Temperate and Frigid heat zones. Longitudes are half-circles that run from pole to pole, and the Prime Meridian at Greenwich is their starting point.
Together, latitudes and longitudes form a grid that helps us to locate any place on the earth precisely. Longitudes are also used to calculate time, and the earth's rotation gives rise to different local times and the need for standard time. The study of latitudes and longitudes is therefore essential for understanding our planet and for navigation around the world.