Chapter Notes: Earth and Solar System

The Solar System

The solar system is like a big family in space. 

• The Sun is at the centre and gives light and heat to the planets.
• The Sun's gravity keeps the planets and other bodies in their orbits.

The Sun - Our Bright Star

The Sun is a very large, hot ball of glowing gases and is the only star in our solar system. It gives us light and heat, which help plants grow and keep the Earth warm.

• The Sun helps plants make food using sunlight.
• We see the Sun rise in the east and set in the west.

The 8 Planets

There are eight planets that move around the Sun. They are different in size, colour and what they are made of. Below are short notes about each planet in their order from the Sun.

1. Mercury (The Nearest Planet)

Mercury is the closest planet to the Sun and the smallest of the eight planets. It is only a little bigger than Earth's Moon. Mercury has a rocky surface and gets very hot during the day and very cold at night.

2. Venus (The Hottest Planet)

Venus is the second planet from the Sun and is similar in size to Earth. Because of a thick, cloudy atmosphere that traps heat, Venus is the hottest planet in the solar system.

3. Earth (Our Home)

Earth is the third planet from the Sun and the only place we know where life exists. It has water, air and a suitable temperature for plants, animals and people.

4. Mars (The Red Planet)

Mars is the fourth planet from the Sun. It looks red because of rusty dust on its surface. Mars is cold, dry and dusty and has a thin atmosphere.

5. Jupiter (The Largest Planet)

Jupiter is the biggest planet in our solar system. It is a gas giant, which means it is mostly made of gases rather than solid rock. All the other planets could fit inside Jupiter many times over.

6. Saturn - The planet with rings

Saturn is famous for its bright rings made of ice and rock pieces. It is the second-largest planet and is also a gas giant.

7. Uranus (The Coldest Planet)

Uranus is the seventh planet from the Sun. It is very cold and appears blue-green because of gases in its atmosphere.

8. Neptune (The Farthest Planet)

Neptune is the eighth and farthest planet from the Sun. It is cold and blue and is also a large planet made mostly of gases.

The Moon - Earth's Friend

Earth has one natural satellite called the Moon.

• The Moon looks bright at night but it only reflects sunlight; it does not make its own light.
• The Moon's gravity affects the oceans and causes tides.
• The Moon shows different shapes called phases as it moves around Earth (for example, crescent and full moon).

Do you know?

• Inner planets: Mercury, Venus, Earth and Mars are called inner planets because they are nearer to the Sun and are rocky.
• Outer planets: Jupiter, Saturn, Uranus and Neptune are called outer planets. Many of them are very large and made mostly of gases.

How Earth Moves

(i) Rotation of Earth

• The Earth spins around an imaginary line through its centre called its axis. This spinning is called rotation.
• The Earth takes about 1 day (24 hours) to complete one rotation.
• Because of rotation we have day and night: one side of Earth faces the Sun (day) while the other side faces away (night).

(ii) Revolution of Earth

• While spinning, the Earth also moves around the Sun. This movement is called revolution.
• The Earth takes about 1 year to go once around the Sun.
• Because of Earth's movement around the Sun (and the tilt of its axis), we have different seasons and a new year every time Earth completes a revolution.

Fun Facts about the Solar System

• The Sun is a star and all the planets move around it.
• Jupiter is the largest planet and Mercury is the smallest.
• Some planets such as Jupiter and Saturn are mainly made of gases; these are called gas giants.
• Our solar system is part of a vast neighbourhood of stars called the Milky Way galaxy.
• Mars has ice at its poles and scientists think it may have had water long ago.
• Comets are icy space bodies that travel around the Sun and sometimes form bright tails.