Chapter Notes: The Earth

Have you ever wondered where we live? We live on a big, round planet called Earth. It is a giant home for people, animals, plants and even tiny insects. The Earth has land, water and air - everything we need to live. When seen from space, Earth looks like a beautiful blue and green ball because most of its surface is covered with water while land has mountains, forests and deserts. The Earth also moves around the Sun and this movement gives us day and night and different seasons. In this chapter we will learn about the Solar System, the shape of the Earth, and how the Earth moves. Let us begin our journey to understand our amazing planet.

Solar System

• The Solar System consists of the Sun, eight planets and their moons, along with asteroids and comets.
• The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
• All these planets move or revolve around the Sun because of the Sun's gravity.

Solar System

Among all these planets, Earth is the only one known to support life. This is because Earth has the right mixture of air, water and land at suitable temperatures. Let us learn more about our home planet.

The Earth

• Long ago, the Earth was formed when tiny pieces of dust and gas in space came together and joined to form our planet.
• Earth is the third planet from the Sun.
• In size, Earth is the fifth largest planet in the Solar System.
• Earth is the only planet that can support life, because it has air, water and suitable temperatures.
• The planet is made up of land, water and air. About two-thirds of its surface is covered by water; the rest is land.
• Surrounding the Earth is a layer of air called the atmosphere. The atmosphere protects living things and helps to keep the planet warm.
• The Earth does not produce its own light. It shines because it reflects light from the Sun.

Earth

Shape of the Earth

The Earth is not a perfectly round ball. It is slightly flattened at the top and bottom (the poles) and a little wider around the middle (the equator). Because of this shape, scientists call Earth an oblate spheroid. You can think of it as being a bit like an orange - mostly round but slightly squashed at the ends.

Here are some simple proofs that show the Earth is spherical in shape:

• During a lunar eclipse the shadow of the Earth falls on the Moon. This shadow is curved and always round, which shows the Earth is spherical.
• When a ship sails away on the sea, you see the top of the ship (the mast) first and the hull disappears last. This happens because the surface of the sea follows the curved shape of the Earth.
• Photographs taken from space by satellites and astronauts show the Earth as a round ball. These pictures give direct visual proof of the Earth's shape.

Viewing of ship

Movement of the Earth

The Earth is never still. It moves in two important ways that affect life on our planet:

1. Rotation - spinning on its own imaginary line called the axis. Rotation causes day and night.
2. Revolution - moving around the Sun along a path called an orbit. Revolution causes the seasons.

1. Rotation of the Earth

• The Earth spins on an imaginary line that passes through its centre from the North Pole to the South Pole; this line is called the axis.
• The spinning of the Earth on its axis is called rotation. The Earth rotates in the direction from west to east.
• The Earth completes one full rotation in about 24 hours. This period of rotation gives us one day.
• The rotation of the Earth causes day and night: the half of the Earth that faces the Sun has daylight and the half that faces away from the Sun has night.

How day and night are formed

• Because the Earth rotates, different parts of the Earth move into and out of sunlight.
• When your part of the Earth faces the Sun you see daylight; when it faces away you see night.
• Sunrise happens when your place on Earth turns towards the Sun. Sunset happens when your place turns away from the Sun.

But Earth does not only spin; it also moves around the Sun. Let us see how this second movement gives us seasons.

2. Revolution of the Earth

• The Earth moves around the Sun in a path called its orbit. This movement is known as revolution.
• It takes the Earth about 365 days and 6 hours to complete one full revolution. This period is called one year.
• Because the extra six hours each year add up, we have a leap year every four years when one extra day (29 February) is added to keep our calendars correct.
• The Earth's axis is slightly tilted. This tilt means that during different parts of the year different parts of the Earth get more sunlight. As a result we have seasons - summer, winter, spring and autumn.

Revolution of the Earth

Conclusion

The Earth is a wonderful planet that provides air, water and land for all living things. It is the third planet from the Sun and has a slightly flattened round shape. The Earth moves in two important ways: rotation (causing day and night) and revolution (causing the seasons). By learning about the shape and movements of the Earth we can better understand why different places have day and night at different times and why seasons change during the year.