1. The term ‘universe’ implies to almost everything that exists in the outer space. It is still a mystery as to how it was formed, but the most prevalent theory is that the universe emerged after the Big Bang. It consists of a large number of galaxies, which further comprise planets, meteors, comets, satellites, etc.

2. The universe consists of a large number of galaxies. Our solar system is found in the Milky Way galaxy. It is also known as Akash Ganga, as it appears to be white in colour. It is believed that our galaxy is home to almost 10,000 stars.

3. Ordinary units of measurement are not used for measuring distance in the universe. Light-year is used as a measure of distance that is equal to the distance covered by light travelling at a speed of 3,00,000 kilometres per second in one year.

4. A cloud of gas and dust particles of which a star is made is known as a nebula. Nebulas are very large bodies that possess their own light. They appear to be dot-like figures in the night sky, as they are very far from the Earth’s surface.

5.The first four planets of the solar system, i.e. Mercury, Venus, Earth and Mars, are known as inner planets. They are made up of hard rock materials. Hence, they are also termed terrestrial planets.

6. Mars, Jupiter, Uranus and Neptune are known as outer planets or gas giants. They are called so because they are made up of gases. They have been categorised so because they share common properties.

7. The Earth is known as the Blue Planet or the Water Planet. It is called so because when the astronauts first saw the Earth from space, it appeared blue in colour because of the presence of water on it.

8. Asteroids are small solid objects that orbit the Sun. They are also known as planetoids or minor planets. There are millions of asteroids found between the orbits of Mars and Jupiter.

9. A meteor is a small piece of rock revolving around the Sun in its orbit. When it enters the Earth’s atmosphere, it lights up and start burning. Hence, it is also called a shooting star. It forms a crater when it hits the surface. One such crater was found in Arizona, USA.

10. Comets are huge masses of snow and rocks that orbit the Sun. They have huge glowing tails. Halley’s Comet was last seen in 1986; it appears after a period of every 76 years. There are around 200 crore comets in our solar system.

11. A constellation is a group of stars in a particular pattern. In ancient civilisations, people saw these constellations as figures of objects, animals, beasts, etc. These constellations had a considerable influence on the lives of the people. The positions of the constellations were used to direct the activities of the people like harvesting, planting and slaughtering.

12. The constellation that is most visible to our naked eyes is Saptarshi. It is a group of seven stars. It was used in ancient times to find directions. The Pole Star, which represents the north direction, can be easily located with the help of Saptarshi. Hence, in earlier times, it was easy to locate directions without the help of a compass.

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