Chapter - Review:

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• The sun is considered the "head" of the solar system.
• Moon diameter is just about a quarter of earth's diameter. 
• The galaxy we live in is called the milky way.
• Small pieces of rocks which move around the sun are called meteoroids.
• Asteroids are the numerous tiny celestial bodies which revolve around the sun and are mainly found between the orbits of mars and Jupiter.
• The Moon takes approximately 27 days to revolve once around the earth.
• Earth appears blue from when seen from the outer space since it has over 2/3^rd water.
• A sphere with its ends flattened at poles (just like earth) is called the geoid.
• venus is called "Earth twin" because it is similar to earth in its shape and size.
• The orbits of plants are elliptical in shape.

 

 Exercise - Question:

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Q1. Answer the following questions briefly :

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

Ans. 

Stars	Planets
- stars emit a large amount of heat and light.   - they are big heavenly bodies.     - there are many stars which we cannot see with our naked eyes.	- they do not have heat and light of their own. They only reflect the light of the sun - planets are called 'wanderers' because they revolve around the sun in their fixed orbits. - planets can be seen with the help of the telescope.

 

(b) What is meant by the 'solar system' ?

Ans. The sun, the planets and satellites together with other minor bodies make up the solar system. The Sun is at the centre of the solar system. The planets revolve around the Sun in their fixed orbits. The satellites revolve around the planets.

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

Ans. The planets according to their distance from the Sun are :

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

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

Ans. Earth is called a unique planet because

(i) Conditions favourable to support life are found only on the earth; it is neither too hot nor too cold.

(ii) Earth has surface water, which is very necessary for our survival.

(iii) It has life giving oxygen and the ozone layer, which protect us from the harmful rays of the sun.

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

Ans. The moon revolves round the earth in about 27 days. It takes exactly the same time to rotate on its axis. To complete both the movements, the Moon takes the same time. This is the reason why we see only one side of the Moon.

(f) What is the universe ?

Ans. The universe is the whole body of stars, planets, satellites and gases. It is endless. Stars are huge bodies of glowing gases e.g. sun. Planets and satellites do not have heat and light of their own, they are lit by the light of the stars.

Q2. Tick the correct answer -

(a) The planet know as the "Earth is twin" is.......

(i) Jupiter (ii) Saturn (iii) Venus

(b) Which is the third nearest planet to the Sun.......

(i) Venus (ii) Earth (iii) Mercury

(c) All the planets move around the Sun in a........

(i) Circular path (ii) Rectangular path (iii) Elliptical path

(d) Asteroids are found between the orbits of.......

(i) Saturn and Jupiter

(ii) Mars and Jupiter

(iii) The Earth and Mars

Ans. (a) (iii), (b) (ii), (c) (iii), (d) (ii), (e) (ii).

Q3. Fill in the blanks:

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

(b) A huge system of stars is called ........

(c) ..........is closest celestial body to our Earth .

(d) ........ is the third nearest planet to the Sun.

(e) Planets do not have their own ......... and ..........

Ans. (a) stars/constellation, (b) galaxy, (c) Moon, (d) Earth, (e) heat/light.

Additional Question:

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Que: Name two celestial bodies visible only in the night sky.

Ans: The moon qand the stars are celestial bodies visible in the night sky.

Que: Why do we not feel the heat and light of the stars, even throught they are so big and hot?

Ans: We do not the heat and light of the stars snice they are very far away.

Que: From which Greek word is the word 'planet' derived?

Ans: The word 'planet' is derived from rthe Greek word 'Planetai'.

Que: What does the solar family of?

Ans: The solar family consists of the sun, planets, their satellites, and asteroids and meteoroids.

Que: What is the shape of the orbits in which plants revolve around the sun?

Ans: The orbits of planets are elliptical in shape.

Que: which planet is called "Earth's twin" and why?

Ans: Venus is called "Earth's twin" because it is similar to earth in its shape and size.

Que: What is "Geoid".

Ans: A sphere with its ends flattened at poles is called the geoid.

Que: Why is earth called "blue planet".

Ans: Earth appears blue from when seen from the outer space since it has over 2/3^rd water. So it is called the blue plants.

Que: What is the difference between the moon and INSAT?

Ans: The moon is a natural satellite of the earth while INSAT is an artifical satellite.

Que: What are meteoroid?

Ans: Small pieces of rocks which which move around the sun are called meteoroids.

Que: What are asteroids?

Ans: Asteroids are numerous tiny celestial bodies which revolve around the sun and are mainly found between the orbits of mars and jupiter.

Que: Name the two extreme shapes of the moon. When and at what intervals do they occur?

Ans: The moon is seen in its two extreme shape on the Full Moon night arid the New Moon night. The Full Moon. The full Moon means the moon in its full circular shape. The New Moon. The New Moon means the moon that can not be a seer. The New Moon occurs on the last day of the hindi calendar month.

Que: What is the pole star? How can the saptarishi be used to locate it?

Ans: The Pole satar is the star that is known to retain its postition in rthe sky always. We can locate the positional of the Pole star with the help of the constellation Saptarishi. If an imaginary line is drawn joining the "pointer stars" of the Saptarishi and extended further, it will point the pole star. The Pole star the pointer stars lie on the same line.

Que: Write a short note on the two plants nearest to the sun.

Ans: Mercury It is the nearest plants to the sun. It takes just about 88 earth days to revolve once aroun the sun. It is extremely hot since it is close to the sun. It is also the smallest plants. Venus, It is the second closest plants to the sun. It is similar to earth in shape and size. It is called "Earth's twin".

Que: How does earth support life?

Ans: The earth has conditions that support life/. It is neither too hot nor too cold. It was both water and air, which are both indispensable for life. Presence of oxygen in the air in an appropriate proportion supports life. These factors make the earth a unique planst.