Solar system, planets and satellites

Solar system

                    A part of the Milky way in which sun occupies a central position of the system holding together all planets, satellites and other heavenly bodies that revolve around it is called solar system.

Planets and satellites 

           The solar system consists of nine planets. They are Mercury,

Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Between Mars and Jupiter is a belt of minor planets called Asteroids. They revolve in elliptical orbits around the sun. The motion of planets in their orbits is due to the force of gravitation of the sun on them. The planet Mercury is nearest to the sun and Pluto is farthest from the sun. Jupiter is the largest of all the planets and Saturn is the second largest. Mercury and Venus are called inferior planets, as their orbits are smaller than that of the earth. The other planets are called superior planets whose orbits are lager than that of the earth.

              In solar system, only the sun emits its own light. The planets appear bright by reflecting the light falling on them from the sun. The planets have heavenly bodies called satellites revolving around them.

              The Kepler's laws of planetary motion and Newton's laws of gravitation along with radiation laws help us to determine various physical properties such as distance, size, period of revolution, mass, surface temperature and atmosphere of planets in solar system. The size of the solar system is equal to the radius of the orbit of Pluto which is about 5.6 x 10⁹ km.,

            In addition to the sun, nine planets and their satellites and asteroids, the solar system contains many bodies called comets and  meteors. These are other types of celestial bodies whose motion is also due to the gravitational force of the sun.

              It is believed that the sun has a total life of about 10 billion years. Out of which, nearby 5 billion years is already over. The sun is made up of extremely hot gases giving out huge flames. Also, sun is the only source of heat and light energy to all the heavenly bodies that revolve around it. The interior of the sun is called photosphere. The temperature of the core is of the order of 14 million kelvin. The outer region of the sun is called the chromosphere and its temperature is of the order of 6000 kelvin.