3rd Class Science Our Universe Our Universe

     Our Universe

Everything which we see in the sky, that is stars, moons, planets, comets, even the earth on which we are living and all other heavenly bodies make our universe.

In this chapter we will study in brief about the important components of universe.

           Solar System

Solar system is having Sun at the center and all the other eight planets with their moons. All these and also the smaller objects like comets, asteroids meteorites etc. revolves around the Sun. These celestial bodies don't fly away as the strong force of gravity of the sun continuously pull them towards itself.

Look at the following picture of our solar system:

         Star

Big ball of burning gas in the sky is called star. Star is a luminous object that produces light of its own. It is seen as a twinkling and shining object in the sky due to the earth's atmosphere. Sun is also a star that has light of its own.

There are about 10000 billions of stars in the universe. Sun is a medium sized and middle aged star nearest to us. People on the earth worship the Sun as it is the ultimate source of energy. No life could exists on this planet without the light and heat of the Sun.

The temperature on the surface of the Sun is almost 5500°c. Gamma rays, x-rays, UV rays, infrared rays and many harmful rays are released from the Sun.

When moon comes in between the earth and the sun, solar eclipse occurs.

Groups of stars are seen in different parts of the sky forming patterns. These patterns resemble to living or non living creatures. Such group of stars are called constellation. Ursa major resembling the shape of big bear, Ursa minor resembling little bear, Orion resembling hunter. Draco resembling dragon which are seen in the sky. Constellations help astronomer in locating things in the sky during night.

Collection of billions of stars in a particular shape is called galaxy. Milky Way is the name of our galaxy, the galaxy closest to us is andromeda. There are billions of galaxies in the universe.

Astronomy is the branch of science that deals with the studying of space and all heavenly bodies. People who study astronomy are called as astronomer.

Look at the following pictures of constellations in the night sky:

    Ursa major                                               Orion                                              Draco  

     I am the biggest member of the solar system. I have my own light and without me plants can't manufacture its food. Who am I?

(a) Earth

(b) Jupiter

(c) Sun

(d) Saturn

(e) Mercury

Answer: (c)

Explanation

Sun is a star that emits heat and light. Plants need sunlight to make its food from carbon dioxide and water. It is the biggest member of the solar system. Therefore, option (c) is correct and rest of the options is incorrect.

    Sun looks bigger and brighter than other stars, for which one of the following reasons?

(a) Because it is big ball of fire

(b) Because it is far away from us

(c) Because it is closest star to us

(d) Because it is young star

(e) All of these

Answer: (c)

Explanation

Sun is a medium sized, middle aged star which is close to us than other, stars. Hence it looks bigger and brighter. Therefore, option (c) is correct and rest of the options is incorrect.