Earth and Other Planets - Class 4 Notes & Olympiad Questions

Solar System

Our Solar System is part of the Milky Way Galaxy, which has billions of stars. The Milky Way Galaxy is just one of many galaxies in our vast Universe.

Movements of the Earth

Rotation

a) Rotation is like when you spin a top and it goes round and round while staying in one spot. The Earth also revolves around an imaginary line that goes through its centre. We can't see this line, so we call it imaginary.
b) It is also known as Earth’s axis of rotation.
c) It takes the Earth 24 hours, or one day, to complete a rotation.
d) As the Earth rotates, different parts of it face the Sun, which gives us daylight. When your side of the Earth is facing away from the Sun, it's nighttime because it's dark.

Some key points about the rotation:

Axis: The axis is an imaginary straight line that goes through the centre of the Earth.

Poles: The North Pole and the South Pole are the two points on the Earth's surface where the axis comes out.

Solar Day: It takes Earth 24 hours to complete one full rotation, which we call a solar day.

How are Days and Nights Formed?

a) Day and night are formed because of the Earth’s rotation.
b) As the Earth spins, one side of it faces the sun, and that's when it's day there. The sun shines on that side, and it's bright and sunny.
c) But on the other side of the Earth, the part that's facing away from the sun, it's night there. It's dark because the sun is not shining on that side.

Revolution

a) The Earth not only spins but also moves around the Sun in a fixed path called an orbit. This movement is called revolution.
b) It takes the Earth 365 days, which we call a year, to complete one revolution around the Sun. This journey around the Sun is what gives us different seasons throughout the year.
c) The Earth's tilt, about 23.5 degrees, also plays a role. It makes the different parts of the Earth face the Sun at different angles, which affects the seasons. That's why sometimes it's warmer and sunny, and other times it's cooler and darker.

Planets of the Solar System

There are two groups of planets in our solar system: the Terrestrial Planets and the Gas Giants.

Terrestrial Planets

a) The Terrestrial Planets are also called the inner planets. They include Mercury, Venus, Earth, and Mars.
b) These planets are the ones closest to the Sun. They are made up of lots of rocks and soil. Earth is one of these planets.

Gas Giants

a) Gas Giants are also known as the outer planets of our solar system. They are Jupiter, Saturn, Uranus, and Neptune.
b) They are really big and have a lot of gas in their atmosphere. It's like they are made up of fluffy clouds. Some of these planets, like Saturn, even have beautiful rings around them.

Mercury

a) It's the smallest and closest planet to the Sun.
b) It doesn't have any moons.
c) It takes 88 days for Mercury to go around the Sun once.

Venus

a) It's the second planet from the Sun.
b) Venus has lots of volcanoes and is covered in clouds.
c) It's the brightest planet in the sky.
d) Venus doesn't have any moons.

Earth

a) It's the third planet from the Sun.
b) Earth is known as the Blue Planet because it's mostly covered in water.
c) It's the only planet known to have life.
d) Earth has one moon.

Mars

a) It's the fourth planet from the Sun.
b) Mars is called the Red Planet because its surface appears reddish.
c) It has two moons.
d) Mars experiences intense dust storms.

Jupiter

a) It's the fifth planet from the Sun and the largest planet in the solar system. It is so big that it can fit all the other planets inside it.
b) It rotates really fast, completing one rotation in 10 hours.
c) Jupiter has a special feature called the Great Red Spot. It's like a gigantic storm that's been going on for a very long time.
d) It's made mostly of gases.
e) Jupiter has 95 moons.

Saturn

a) It's the sixth planet from the Sun and the second largest planet.
b) Saturn has beautiful rings made of rocks and ice.
c) It has 146 moons.

Uranus

a) It's the seventh planet from the Sun.
b) It is very cold and windy.
c) It's known as the sideways planet because of its unique feature of orbiting on its side.
d) Uranus has 27 moons.

Neptune

a) It's the eighth and farthest planet from the Sun.
b) Neptune is icy, cold, and windy.
c) It has the slowest revolution speed in the solar system.
d) Neptune has 14 moons.

Why do Planets appear Bright?

a) The planets in our solar system appear bright because they are closer to us compared to the stars.
b) Even though the planets are smaller than the stars, they look almost the same size as the stars because they are closer to us.
c) Planets don't make their own light as stars do. Instead, they reflect the light from the Sun, just like how Moon reflects sunlight. This is why planets seem steady and don't twinkle as stars do.