4th Class Science Our Universe

                                                                  Our Universe

Our Universe

Our universe consists of number of stars, planets including our earth and moons.

Solar System

The sun and the eight planets belong to a family called solar system. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. All of them revolve in fixed path called orbit. Planets rotate on their axis also. Most planets have their satellites which revolve around them. Satellite does not have its own light. Man has also made some satellites for weather forecasting and to help in communication which are known as artificial satellites, for example, Aryabhata, Rohini etc.

Stars and Planets

A star is a huge ball of hot gases. It gives out heat and light. Planets do not have any heat or light of their own. They appear bright because they reflect the light of the stars. They revolve around stars. The sun is actually a star because it has its own heat and light. It is a huge sphere of hot gases. The earth and other seven planets that revolve around the sun get heat and light from the sun.

The sun is the main source of energy in our solar system. The planet Mercury is closest of the sun, followed by Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. They revolve around the sun in fixed path called orbit. Stars are far apart from each other. Distance between stars is measured in light years. The distance travelled by light in one Year is called light year.

The planets also rotate on their axis. Most of the planets have satellites. A satellite is a heavenly body that revolves around planets. It does not have any light of its own. The moon is a natural satellite of the Earth. It shines as it reflects sunlight from its surface. The moon does not have an atmosphere to protect it from extreme heat or cold. Some satellites in the sky are artificial. They have been sent up by scientists of different countries to study space, to forecast weather or to help in communication. The first one of these was Sputnik 1. Some others are Aryabhata,

Rohini, INSAT, etc.