The sun is in the centre of the solar system. There are eight planets in our solar system. In order of their distance from the sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Apart from the stars, planets and satellites, there are numerous tiny bodies which also move around the sun. These bodies are called asteroids.
They are found between the orbits of Mars and Jupiter The small pieces of rocks which move around the sun are called meteoroids.
1. How does a planet differ from a star?
Planets: They have no light or heat of their own. They are lit by the light of stars.
Star: They are hot. They are made up of gases. They have their own heat which they emit in large amounts.
2. Why is Earth called a unique planet?
The Earth is called a unique planet due to the following reasons:
- The Earth is neither too hot nor too cold. The Earth is a unique planet in the sense that it provides all things which are necessary for the growth and development of life.
- It contains water and air, which is essential for our survival.
- Air has life-supporting gases like oxygen.
3. Why do we see only one side of the moon always?
We see only one side of the moon as it revolves around the Earth in about 27 days and 8 hours and takes the same time to complete one spin.
4. What is the Universe?
The Universe is the whole body of stars, planets, dust and gases. It is an infinite space consisting of millions of galaxies.
5. Define celestial bodies.
The heavenly bodies which shine in the sky are called celestial bodies.
6. On what basis are stars classified?
The stars can be classified according to their physical characteristics like; (i) size (ii) temperature (iii) colour and (iv) brightness.
7. What are planets?
Some celestial bodies don’t have their own light and heat. They are lit by the light of the stars. Such bodies are called planets. These are eight planets in our solar system - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. They revolve around the Sun.
8. What are orbits?
All planets in solar system move around the sun in fixed path. These paths are elongated and they are called orbits.
9. Why is earth called blue planet?
From the outer space, the earth appears blue because its 2/3rd surface is covered by water. It is therefore, called a blue planet.