1 The Universe The universe means everything that exists. It consists of the whole space in which we live, that is, the earth together with all the planets and stars. The origin of the universe is explained by the Big Bang Theory. According to this theory, everything in the universe was initially hot and dense and slowly it started cooling and condensing. The systems that were formed thus are called galaxies. There are millions of galaxies in the universe. The Milky Way and Andromeda are examples of galaxies. Night sky Big Bang We see the sky decorated with moon, planets and stars at night. But why do we not see these glittering stars during the day time? The sun s bright light makes them disappear during the day. Try This Sketch the sky and other heavenly bodies you observe at night. Milky Way A galaxy is a massive cluster of hundreds and millions of stars orbiting around a centre. All the stars which we see from the earth belong to the earth s galaxy 1
or the Milky Way. The Milky Way is the name given to the faint band of light that stretches across the sky that we see at night. The heavenly bodies in the Milky Way are the sun, the moon, the stars, the planets and the comets. Stars The Milky Way Stars are big balls of fire that give out heat and light. The flames of fire that come out of the stars make them twinkle. The sun is one of the stars in the milky way which gives out its own light and heat. Many of the stars are much bigger than the sun, but they appear very small, as they are very far away from the earth. In the sky, stars are grouped in a particular way. The formation of stars in groups is called a constellation. Satellites or Moons These are heavenly bodies that revolve around a planet in the solar system. These satellites are known as followers as they follow the planets in their orbits around the sun. 2
Planets Planets are heavenly bodies that revolve around the sun. The planets are also known as wanderers. They move around the sun on a set path known as orbit. They do not produce heat or light but reflect the light of the sun. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune are the eight planets that move around the sun. Planets are different from the stars. While planets revolve around the sun, the stars are stationary and they produce their own light and heat. Mercury Mercury is the smallest planet. It is also the nearest to the sun. Mercury has no moons or satellites. Earth Venus Venus is known as the twin planet of the earth, as it is almost of the same size as the earth. It is the brightest and the hottest among all planets. It is also known as morning star or evening star, as it is seen either just before the sunrise or just after the sunset. Venus has no moons. The earth is the third planet from the sun and the only planet that supports life. Two-thirds of the earth s surface are covered with water. The earth is also known as the blue planet. It has only one moon. Mars Mars is known as the red planet and is the fourth planet from the sun. It has two moons. 3
Jupiter Jupiter is the largest of all planets. It has faint rings around it. It has many moons. Uranus Saturn Saturn is known as the ringed planet and is as large as Jupiter. There are many bright rings around Saturn making it the loveliest of all planets. It also has many moons. Uranus is a very unique planet. It is the seventh planet from the sun. It is the only planet which rolls on its sides, on its axis. The other planets spin upright. Uranus is also encircled by many thin rings and moons. Comets Neptune Neptune is the farthest planet from the sun. It has faint rings and moons around it. The tailed stars are called comets. Comets are lumps of ice and dust. They travel around the sun. As the comet approaches the sun, some of its frozen gases evaporate creating a tail of dust and ice which we can see from the earth. Asteroids Asteroids are small planetary bodies seen mostly between the orbits of Mars and Jupiter. They are also called planetoids. 4
The Solar System The sun is the nearest star to our earth. The sun and all the planets along with satellites form the solar system. The word solar means of the sun. neptune saturn uranus mars mercury sun venus earth jupiter Do you know? 1. There are millions of galaxies in the universe. 2. The rays of the sun take 8 minutes to reach the earth s surface. 3. Pluto, which was the ninth planet in the solar system, lost its position and has been declared as a dwarf planet or Pluton since September 2006. 4. The constellation helped farmers in ancient period to decide seasons for planting and reaping crops. Let s Recall The universe is a vast open space that contains billions of clustered stars. A galaxy is a massive cluster of hundreds and millions of stars orbiting around a centre. Stars are big balls of fire. They produce heat and light. The sun and all the planets along with their satellites form the solar system. 5
Planets are heavenly bodies that revolve around the sun on a set path known as orbit. Satellites are heavenly bodies that revolve around the planets. Now I Can Answer A. Tick the correct answer. 1. The Milky Way is: earth s orbit fireball of gases a galaxy 2. The largest among the planets in the solar system is: Saturn Jupiter Earth 3. The earth is known as: the red planet the ringed planet the blue planet 4. The farthest planet in the solar system is: Neptune Uranus Mercury 5. Stars give out: B. Fill in the blanks. only heat only light both heat and light 1. The set path along which the planets move around the sun is known as their. 2. The are heavenly bodies. They do not produce heat and light. 3. The earth receives heat and light from the. 4. The is the only natural satellite of the earth. 5. A tailed star is called a. C. Give one word/few words answers. 1. What are comets called? 2. What are stars? 6
3. What is the other name of planets? 4. What explains the origin of the universe? 5. Which planet does not spin upright? 6. Name the galaxy we see in the sky. D. Answer the following questions. 1. What do you mean by the universe? 2. What is a galaxy? 3. Which planets revolve around the sun? 4. What is solar system? 5. Differentiate between the stars and the planets. E. Match the following planets with the names they are also known by. Column A Column B 1. Uranus (a) Ringed Planet 2. Venus (b) Red Planet 3. Earth (c) Twin Planet 4. Mars (d) Blue Planet 5. Saturn (e) Farthest planet from the sun F. Give reasons. (HOTS) 1. We do not see any heavenly body other than the sun during the day. 2. The sun is a star. 3. All stars look very small except the sun. 4. Planets do not twinkle like stars. Activity Draw the picture of the solar system and name all the members of the solar family. 7