8th Class Science Stars and the Solar System Solar System

     Solar System

The family of eight planets along with the Sun is called so/or system. In solar system, the Sun is at the nucleus, and all the other planets revolve around it in a fixed orbit. There are many small celestial bodies such as Asteroid, Comets and Meteoroids. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The ninth planet Pluto has just been removed from the family of the solar system. The smaller heavenly bodies, which revolves around the planets, as the planets revolve around the Sun, is called satellites.  Asteroids are small rocky bodies, which revolve around the Sun between the orbits of the planets Mars and Jupiter. The gravitational force of the Sun keeps the solar system together, and controls the movement of planets and other members of the solar system.

The Jupiter is the biggest planet and Mercury the smallest planet. The nearest planet is the Mercury and the farthest planet is Neptune. The planets do not have the light of their own. However, they shine because they reflect the light of the Sun falling on them. The best way to differentiate between the planet and stars is that, the stars have the light of their own and hence they twinkle, and the planets do not have the light of their own so do not twinkle. Also the planets keep changing their position with respect to stars in the night. Each planet has its own orbit,along which it revolves around the Sun. The first four planets Mercury, Venus, Earth and Mars are called the inner planets. The rest of the planet are called the outer planets. The four outer planets are mainly made up of hydrogen and helium gas. The inner planets are made up of rocks and metals.

                                                   Solar System  

Some Facts about the Planets

           Mercury

This planet is nearest to the Sun, therefore, it is hottest of all planets. It is also the smallest planet of the solar system. It is made up of rocks and has craters on its surface. It is known as the morning stars, as it can be seen only in the morning. It has no natural satellites and is also known as Budh graha.

            Venus

This is the closest planet to the earth. Its axis of rotation is opposite to that of the Earth. The Earth rotates from west to east, whereas Venus rotates from east to west. Hence, the Sun rises in the west and set in the east on Venus. The atmosphere of Venus mainly consists of carbon dioxide gas, so it is the brightest planet in our solar system. It is also the hottest planet in our solar system, as the large amount of carbon dioxide gas in its atmosphere traps the heat from the sunlight. It has no natural satellite. There is no life on the surface of the Venus, as there is no water and air.

          Earth

This is the third planet of our solar system and the only planet where life exists. The major factors responsible for supporting life on earth are:

(i) The temperature of the earth is optimum for the existence of lives.

(ii) The presence of life gases and water on the surface of earth helps the life to flourish.

(iii) Earth also has a protective layer of ozone, which protects harmful ultraviolet radiations coming from the Sun, to reach surface.

The atmosphere of earth consists of mainly Nitrogen (78%), Oxygen (21%), Carbon dioxide (0.3%) and remaining are the mixture of other gases. It takes almost 24 hours to complete one rotation around its own axis, and 365 days and 6 hours, to complete one revolution around the Sun. Certain consequence, such as causing of days and nights, is due to rotation of earth on its own axis. The change of season is due to the revolution of earth around the Sun. It has one natural satellites called Moon.

           Mars

This is the fourth planet of the solar system and also known as the red planet. It is far from the Sun, so is very cold. This planet is very similar to the earth, though its mass is smaller than that of the earth. It has rocks on its surface and atmosphere mainly consists of carbon dioxide gas, with small amount of nitrogen, oxygen, noble gases and water vapour. It is estimated that in near future the lives may be possible on the surface of the Mars, if its atmospheric condition changes. It has two natural satellites, Phobos and Deimos.

            Jupiter

This is the fifth planet of our solar system, and the biggest of all. The mass of Jupiter is more than the combined mass of the remaining planets. Its diameter is 11 times and mass 318 times, than that of the earth. It is so large that, about 1300 earth can be placed inside it. This planet mainly consists of hydrogen and helium gases. Its atmosphere also contains poisonous gases like methane and ammonia. It has 28 natural satellites. It is also known as Brihaspati graha. The four main satellites of the Jupiter are Amalthea, Lo, Europa, Ganymede and Callisto.

             Saturn

This is the sixth and the second largest planet of our solar system. Its atmosphere mainly consists of hydrogen and helium and density is less than any other planets, including water. It has a colourful ring around it. The rings of Saturn is made up of tiny particles. Its surface temperature is very low, so no life is possible on the Saturn. It has 30 natural satellites. Some of the natural satellites are Atlas, Calypso, Dione, Enceladus, Helene, Janus, etc.

             Uranus

This planet is the seventh member of our solar system. It was discovered with the help of telescope. It is the third biggest planet of our solar system. It rotates from east to west on its axis. It is mainly made up of hydrogen and helium. It has 21 satellites. Some of them are Miranda, Ariel, Umbriel, Titania and Oberon.

             Neptune

This is the eighth planet of our solar system. It was also discovered with telescope. It is mainly made up of liquid, frozen hydrogen and helium gas. It has 8 natural satellites. Some of them are Ring, Nereid, Proteus, Triton, Larrisa etc. Triton is the biggest satellite of Neptune.

           All the planets have their own natural satellites revolving around them in fixed orbit. Phobos and Diemos are also the natural satellite of one of the planets. Name the planet.

(a) Mercury

(b) Venus

(c) Mars

(d) Jupiter

(e) None of these

Answer: (c)

         We are familiar with the planets since early days. But in those days not much information was available about these planets. Some of the planets, which are far away from the earth came into light only after the invention of telescope. Which was the first planet to be discovered by the telescope?

(a) Venus

(b) Uranus    

(c) Pluto

(d) Saturn

(e) None of these

Answers: (b)

Explanation

The first planet to be discovered with the help of telescope is Uranus.