Class 6 𝐓𝐇𝐄 𝐒𝐎𝐋𝐀𝐑 𝐒𝐘𝐒𝐓𝐄𝐌 - 𝐓𝐡𝐞 𝐒𝐮𝐧 , 𝐏𝐥𝐚𝐧𝐞𝐭𝐬 , 𝐓𝐡𝐞 𝐄𝐚𝐫𝐭𝐡

### 𝐓𝐇𝐄 𝐄𝐀𝐑𝐓𝐇 𝐈𝐍 𝐓𝐇𝐄 𝐒𝐎𝐋𝐀𝐑 𝐒𝐘𝐒𝐓𝐄𝐌

color{green}(•) How wonderful it is to watch the sky after sunset! One would first notice one or two bright dots shining in
the sky.

color{green}(•) Soon you would see the number increasing. You cannot count them any more.

color{green}(•) The whole sky is filled with tiny shining objects- some are bright, others dim.

color{green}(•) It seems as if the sky is studded with diamonds.

color{green}(•) They all appear to be twinkling. But if you look at them carefully you will notice that some of them do not twinkle as others do.

color{green}(•) They simply glow without any flicker just as the moon shines.

color{green}(•) Along with these bright objects, you may also see them on on most of the days.

color{green}(•) It may, however, appear at different times, in different shapes and at different positions.

color{green}(•) You can see the full moon only once in about a month's time; It is 𝐅𝐮𝐥𝐥 𝐦𝐨𝐨𝐧 night or Poornima.

color{green}(•) A fortnight later, you cannot see it at all. It is a 𝐍𝐞𝐰 𝐌𝐨𝐨𝐧 night or Amavasya.

color{green}(•) On this day, you can watch the night sky best, provided it is a clear night.

color{green}(•) Do you wonder why can't we see the moon and all those right tiny objects during day time? It is because the very bright light of the sun does not allow us to see all these bright objects of the night sky.

color{green}(•) The sun, the moon and all those objects shining in the night sky are called celestial bodies.

color{green}(•) So e celestial bodies are very big and hot. They are made up of gases.

color{green}(•) They have their own heat and light, which they emit in large amounts.

color{green}(•) These celestial bodies are called 𝐬𝐭𝐚𝐫𝐬.The sun is a star.

color{green}(•) Countless twinkling stars in the night sky are similar to the sun.

color{green}(•) But we do not feel their heat or light, and they look so tiny because they are very very far from us.

color{green}(•) You must have noticed. that all objects look smaller when seen from a distance.

color{green}(•) How small an aeroplane looks when it is flying at a great height!

color{green}(•) While watching the night sky, you may notice various patterns formed by different groups of stars.

color{green}(•) These are called 𝐜𝐨𝐧𝐬𝐭𝐞𝐥𝐥𝐚𝐭𝐢𝐨𝐧𝐬.

color{green}(•) Ursa Major or Big Bear is one such constellation.

color{green}(•) One of the most easily recognisable constellation is the Saptarishi (Saptaseven, rishi-sages).

color{green}(•) It is a group of seven stars ( Figure 1.1 ) that forms a part of Ursa Major Constellation.

In ancient times, people used to determine directions during the night with the help of stars.

color{green}(•) The North star indicates the north direction.

color{green}(•) It is also called the Pole Star. It always remains in the same position in the sky.

color{green}(•) In ancient times, people used to determine directions during the night with the help of stars.

color{green}(•) The North star indicates the north direction.

color{green}(•) It is also called the Pole Star. It always remains in the same position in the sky.

color{green}(•) We can locate the position of the 𝐏𝐨𝐥𝐞 𝐒𝐭𝐚𝐫 with the help of the Saptarishi.

color{green}(•) Look at Figure 1.1. You will notice that, if an imaginary line is drawn joining the pointer stars and extended further, it will point to the Pole Star.

color{green}(•) Some celestial bodies do not have their own heat and light.

color{green}(•) They are lit by the light of the stars. Such bodies are called planets.

color{green}(•) The word ‘planet’ comes from the Greek word “Planetai” which means ‘wanderers’.

color{green}(•) The earth on which we live is a planet. It gets all its heat and light from the sun, which is our nearest star.

color{green}(•) If we look at the earth from a great distance, say the moon, it will appear to be shining just as the moon.

color{green}(•) The moon that we see in the sky is a satellite. It is a companion of our earth and moves round it.

color{green}(•) Like our earth, there are eight other planets that get heat and light from the sun.

color{green}(•) Some of them have their moons too

### 𝐓𝐇𝐄 𝐒𝐎𝐋𝐀𝐑 𝐒𝐘𝐒𝐓𝐄𝐌

color{green}(•) The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system.

color{green}(•) We often call it a solar family, with the sun as its Head.

### 𝐓𝐡𝐞 𝐒𝐮𝐧

color{green}(•) The sun is in the centre of the solar system.

color{green}(•) It is huge and made up of extremely hot gases.

color{green}(•) It provides the pulling force that binds the solar system.

color{green}(•) The sun is the ultimate source of heat and light for the solar system.

color{green}(•) But that tremendous heat is not felt so much by us because despite being our nearest star, it is far away from us.

color{green}(•) The sun is about 150 million km away from the earth.

### 𝐏𝐥𝐚𝐧𝐞𝐭𝐬

color{green}(•) There are eight planets in our solar system.

color{green}(•) In order of their distance from the sun, they are :

color{green}(•) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

color{green}(•) All the eight planets of the solar system move around the sun in fixed paths.

color{green}(•) These paths are elongated. They are called orbits.

color{green}(•) Mercury is nearest to the sun.

color{green}(•) It takes only about 88 days to complete one round along its orbit.

color{green}(•) Venus is considered as 'Earth's-twin' because its size and shape are very much similar to that of the earth.

color{green}(•) Till recently (August 2006). Pluto was also considered a planet.

color{green}(•) However, in a meeting of the International Astronomical Union, a decision was taken that Pluto like other celestial objects (Ceres, 2003 UB_(313)) discovered in recent past may be called 'dwarf planets."

### 𝐓𝐡𝐞 𝐄𝐚𝐫𝐭𝐡

color{green}(•) The earth is the third nearest planet to the sun.

color{green}(•) In size, it is the fifth largest planet.

color{green}(•) It is slightly flattened at the poles.

color{green}(•) That is why, its shape is described as a 𝐆𝐞𝐨𝐢𝐝 . Geoid means an earth-like shape.

color{green}(•) Conditions favourable to support life are probably found only on the earth.

color{green}(•) The earth is neither too hot nor too cold .

color{green}(•) It has water and air, which are very essential for our survival.

color{green}(•) The air has life-supporting gases like oxygen.

color{green}(•) Because of these reasons, the earth is a unique planet in the solar system.

color{green}(•) From the outer space, the earth appears blue because its two - thirds surface is covered by water.

color{green}(•) It is therefore , called a blue planet.