Class 6 𝐓𝐡𝐞 𝐌𝐨𝐨𝐧 , 𝐀𝐬𝐭𝐞𝐫𝐨𝐢𝐝𝐬 , 𝐌𝐞𝐭𝐞𝐨𝐫𝐨𝐢𝐝𝐬 , 𝐄𝐱𝐞𝐫𝐜𝐢𝐬𝐞𝐬

### 𝐓𝐡𝐞 𝐌𝐨𝐨𝐧

color{green}(•) Our earth has only one satellite, that is, the moon.

color{green}(•) Its diametre is only one-quarter that of the earth.

color{green}(•) It appears so big because it is nearer to our planet than other celestial bodies.

color{green}(•) It is about 3,84,400 km away from us.

color{green}(•) Now you can compare the distance of the earth from the sun and that from the moon.

color{green}(•) The moon moves around the earth in about 27 days.

color{green}(•) It takes exactly the same time to complete one spin.

color{green}(•) As a result, only one side of the moon is visible to us on the earth.

color{green}(•) The moon does not have conditions favourable for life.

color{green}(•) It has neither water nor air. It has mountains, plains and depressions on its surface.

color{green}(•) These cast shadows on the moon’s surface. Look at the full moon and observe these shadows.

### 𝐀𝐬𝐭𝐞𝐫𝐨𝐢𝐝𝐬

color{green}(•) Apart from the stars, planets and satellites, there are numerous tiny bodies which also move around the sun.

color{green}(•) These bodies are called asteroids.

color{green}(•) They are found between the orbits of Mars and Jupiter (Figure 1.2). Scientists are of the view that asteroids are parts of a planet which exploded many years back.

### 𝐌𝐞𝐭𝐞𝐨𝐫𝐨𝐢𝐝𝐬

color{green}(•) The small pieces of rocks which move around the sun are called meteoroids.

color{green}(•) Sometimes these meteoroids come near the earth and tend to drop upon it.

color{green}(•) During this process due to friction with the air they get heated up and burm.

color{green}(•) It causes a flash of light.

color{green}(•) Sometimes, a meteor without being completely burnt, falls on the earth and creates a hollow.

color{green}(•) Do you see a whitish broad band, like a white glowing path across the sky on a clear starry night?

color{green}(•) It is a cluster of millions of stars.

color{green}(•) This band is the Milky Way galaxy (Figure 1.6).

color{green}(•) Our solar system is a part of this galaxy.

color{green}(•) In ancient India, it was imagined to be a river of light flowing in the sky.

color{green}(•) Thus, it was named Akash Ganga.

color{green}(•) A galaxy is a huge system of billions of stars, and clouds of dust and gases.

color{green}(•) There are millions of such galaxies that make the Universe.

color{green}(•) It is difficult to imagine how big the universe is. Scientists are still trying to find out more and more about it.

color{green}(•) We are not certain about its size but we know that all of us – you and I belong to this universe.

### 𝐄𝐱𝐞𝐫𝐜𝐢𝐬𝐞𝐬

color{green}(•) 𝟏. 𝐀𝐧𝐬𝐰𝐞𝐫 𝐭𝐡𝐞 𝐟𝐨𝐥𝐥𝐨𝐰𝐢𝐧𝐠 𝐪𝐮𝐞𝐬𝐭𝐢𝐨𝐧𝐬 𝐛𝐫𝐢𝐞𝐟𝐥𝐲.

(a) How does a planet differ from a star?

(b) What is meant by the ‘Solar System’?

(c) Name all the planets according to their distance from the sun.

(d) Why is the Earth called a unique planet?

(e) Why do we see only one side of the moon always?

(f) What is the Universe ?

color{green}(•) 𝟐. 𝐅𝐢𝐥𝐥 𝐢𝐧 𝐭𝐡𝐞 𝐛𝐥𝐚𝐧𝐤𝐬.

(a) A group of ________ forming various patterns is called a ________.

(b) A huge system of stars is called________.

(c) ________is the closest celestial body to our earth.

(d) ________is the third nearest planet to the sun.

(e) Planets do not have their own________ and ___________________.