What is the Universe?
The universe is a vast infinite space which includes the earth and all the heavenly bodies in the sky. The sky contains the Sun, Planets (their moons), Stars, Galaxies, Comets, Asteroids, and Satellites.
Star is a heavenly body which has the light of its own. You can see stars twinkling in the sky at night. At the moonless night and try to count the number of stars which you can see with your naked eye. You may be able to count around 2000 to 3000 stars in your naked eye. But the help of a small telescope you can see around 100,000 stars and most powerful one you can see more than millions (1,000,000) & trillions (1,000,000,000,000) stars.
The stars are the very large object and several times bigger than our earth. Some are very small and some are even bigger than the sun. They appear so small because they are very far away from us.
The Sun is also a star and it gives off light all the time.
Planets are the heavenly bodies which revolve around the sun. They do not produce their own light but reflect the light of the sun that falls on them. Planets are disc shaped. The planets are not twinkle, brighter than stars. There are eight planets comprised in our universe.
A vast collection of stars, dust, and gas held together by the gravitational attraction between its components. Galaxies are usually classified as Elliptical, Spiral or Irregular shape.
Milky Way System
The Milky Way System is a galaxy that belongs to our Solar System. There are some 300 billion stars in the system. The age of the system is more than 13 billion years. Most of the stars in the Milky Way lie in the galactic disk close to the nucleus. Our Solar System lies about 28,000 light years from the center.
A light year means for “The Distance Travelled by Light in One Year”. The speed of the light is 300,000 km per second. Therefore one light year is 9.5 X 1,000,000,000,000 (10 Trillion) kilometers.
The sun is nearly 8 light minutes away from the earth. It means that light from the sun takes nearly 8 minutes to reach the earth.