1. How does a planet differ from a star ?

2. What is meant by the solar system?

The term solar system refers to the " family" of the Sun. The Sun is a star around which eight planets, among other celestial objects, revolve in orbits. This whole system of bodies is called the solar system. The Sun is the "head" of this system.

3. Name all the planets according to their distance from the sun?

     The list of planets in the order of their distance from the Sun is as follows :

               (i)  Mercury

              (ii)  Venus

              (iii)  Earth

              (iv)   Mars

              (v)  Jupiter

             (vi)   Saturn

             (vii)  Uranus

            (viii)  Neptune

4. Why is the Earth called a unique planet?

The Earth is regarded as a unique planet because of the following reasons;

         * It is the only planet known to support life.It has oxygen and water present in proportions that allow life to thrive.

         * It also has a temperature range that supports life.

         * The proportion of water present is about two - thirds of the surface of earth when compared to land.

5. Why do we see only one side of the moon always ?

One revolution of the moon around the earth takes about 27 days. Incidentally, the moon's rotation about its own axis also takes nearly the same time. One day of the moon is equal to 27 Earth days. So only one side of the moon can be seen from the earth.

6. What is the Universe ?

The Universe is the largest unit in whch we live. It is a collection of galaxies. There is only one Universe, and everything that exists,in this Universe itself.   

8. Name two celestial bodies visible only in the night sky?

The moon and the stars are celestial bodies visible in the night sky.

9. Why do we not feel the heat and light of the stars, even though they are so big and hot ?

We do not feel the heat and light of the stars since they are very far away.

10. From which Greek word is the word 'planet' derived ?

The word 'planet ' is derived from the Greek word 'Planetai'.

11. What does the solar family consist of ?

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

12. What is the shape of the orbits in which planets revolve around the sun ?

The orbits of planets are elliptical (i.e. elongated) in shape.

13. Which planet is called "Earth's twin" and why ?

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

14. What is "Geoid" ?

A sphere with its ends flattended at poles (just like earth) is called geoid.

15. Why is earth called "blue planet"?

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

16. How much time does the moon take to revolve once around the earth?

The moon takes approximately 27 days to revolve once around the earth.

17. What is the difference between the moon and INSAT?

The moon is a natural satellite of the earth while INSAT is an artificial satellite.

18. What are asteroids ?

Asteroids are the numerous tiny celestial bodies which revolve around the sun and are mainly found between the orbits of Mars and Jupiter.

19. What is a meteoroid ?

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

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

The moon is seen in its two extreme shapes on the Full Moon night and 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 cannot be seen.

The New Moon occurs on the fifteenth day and the Full Moon occurs on the last  day of the Hindi calender month.

21.  What is the Pole Star ? How can the Saptarishi be used to locate it ?

The Pole Star is the star that is known to retain its position in the sky always. We can locate the position 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 to the Pole Star.

22.  Write a short note on the two planets nearest to the sun.

Mercury:  It is the nearest planet to the sun. It takes just about 88 earth days to revolve once around the sun. It is extremely hot since it is close to the sun. It is also the smallest planet.

Venus:  It is the second closest planet to the sun. It is similar to earth in shape and size. It is called "Earth's twin".

23. How does earth support life ?

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

24. Write short notes on the following:

       (a) The sun

       (b) The moon

       (c) Galaxy

(a) The sun is considered the "head of the solar system. It is a star, although it is smaller and less bright than most other  stars. It is a huge celestial body made up of extremely hot  gases. It provides heat and light for the whole of the solar system. Life on earth depends on many factors, and sunlight is one of them. The sun is about 150 million kilometers away from earth.

(b) The moon is the only natural satellite of our planet earth. Its diameter is just about a quarter of the earth's diameter. It is comparatively closer (3,84,400 kilometers away) to earth than all other celestial bodies. It does not support life. It revolves around the earth and rotates about its own axis in about the same time, due to which only one side of the moon is visible to us.

(c) Galaxy is a term that refers to billions of stars,clouds of dust and gases, and other celestial bodies considered as a single unit.The only bigger unit is the universe,i.e.galaxies make up the universe.The galaxy we live in is called the Milky Way.

25. Draw a diagram showing the eight planets of the solar system in their orbits around the sun. Also prepare a table mentioning the length of their days and years.

     Planet                                         Length of year                          Length of day              

     Mercury                                     59 days                                  88 days

     Venus                                        243 days                                255 days

     Earth                                         1 day (= 24 hours)                  1 year(= 365 days)

     Mars                                          1 day (= about 24 hours)         687 days

    Jupiter                                         9.93 hours                             11.92 years

    Saturn                                         10.67 hour                             29.42 years

    Uranus                                        17.23 hour                             84 years

    Neptune                                      16.12 hours                            164 years

     [ Remark :  1 day refers to 1 Earth day : 1 year refers to 1 Earth year. For example the table tells that 1 Jupiter year is as long as 11.92 Earth years, and that 1 Mars day is nearly as much as 1 Earth day.]