NCERT Class 8 Science Stars And The Solar System

STARS AND THE SOLAR SYSTEM

Paheli and Boojho visited their grandparents’ village during summer break. After dinner, they went on to the roof of the house. It was a clear cloudless night. They were surprised to see a large number of bright stars in the sky. They had never seen such a beautiful scene in their city (Fig. 17.1). at a place where there are no bright lightsand the atmosphere is clear. Look at the sky on a dark, clear night. You see the entire sky dotted with countless stars, some bright and some not so bright. Observe them carefully. Do all of them appear to twinkle? Do you find any star-like object which does Paheli wondered, why the village sky was so different from the night sky in big cities? Her grandfather explained that due to bright light, smoke and dust, sky in big cities is rarely clear. Night sky watching can be a fascinating experience not twinkle? The objects which do not twinkle are planets. The moon is the brightest object in the night sky. The stars, the planets, the moon and many other objects in the sky are called celestial objects.

17.1 The Moon

Activity 17.1

Observe the moon continuously for several nights, preferably from one full moon to the next. Make a sketch of the moon every night in your note book and note from the day of the full moon. Also note everyday the part of the sky (east or west) in which the moon is seen. Is there a change in the shape of the moon everyday? Are there days when the shape of the moon appears to be perfectly round? Are there days when the moon cannot be seen at all even if the sky is clear? The day on which the whole disc of the moon is visible is known as the full moon day. Thereafter, every night the size of the bright part of the moon appears to become thinner and thinner. On the fifteenth day the moon is not visible. This day is known as the new moon day. The next day, only a small portion of the moon appears in the sky. This is known as the crescent moon. Then again the moon grows larger every day. On the fifteenth day once again we get a full view of the moon. The various shapes of the bright part of the moon as seen during a month

are called phases of the moon (Fig. 17.2). Let us try to understand why phases of the moon occur. You have studied in Chapter 16 that the moon does not produce its own light, whereas the Sun and other stars do. We see the moon because the sunlight falling on it gets reflected towards us (Fig. 17.3). We, therefore, see only that part of the moon, from which the light of the Sun is reflected towards us. these positions in your notebook. In which part of the sky would you lookfor the full moon?

The size of the illuminated part of the moon visible from the Earth increases each day after the new moon day. After the full moon day, the sunlit part of the moon visible from the Earth decreases in size every day. The Moon’s Surface The moon is a fascinating object for poets and story-tellers. But when  astronauts landed on the moon, they found that the moon’s surface is dusty and barren. There are many craters of different sizes. It also has a large number of steep and high mountains (Fig. 17.7) Some of these are as high as the highest mountains on the Earth.

17.2 The Stars

What other objects do you see in the night sky? There is a large number of stars in the sky. Observe carefully on a dark night and from a place away from a big city. Are all the stars equally In fact, the stars are present in the sky during the day-time also. However, they are not visible then because of the bright sunlight. Observe some prominent star or a group of stars in the sky for about two hours or more. What do you find? Do you find any change in the positions of stars in the sky? You will find that the stars appear to move from east to west. A star which rises in the east in the evening, sets in the west in the early morning. Why do stars appear to move from east to west? Let us find out.

Exercises

Choose the correct answer in Questions 1-3 :

1. Which of the following is NOT a member of the solar system?

(a) An asteroid

(b) A satellite

(c) A constellation

(d) A comet

2. Which of the following is NOT a planet of the sun?

(a) Sirius

(b) Mercury

(c) Saturn

(d) Earth

3. Phases of the moon occur because

(a) we can see only that part of the moon which reflects light towards us.

(b) our distance from the moon keeps changing.

(c) the shadow of the Earth covers only a part of moon’s surface.

(d) the thickness of the moon’s atmosphere is not constant.

4. Fill in the blanks:

(a) The planet which is farthest from the Sun is ____________ .

(b) The planet which appears reddish in colour is ____________ .

(c) A group of stars that appear to form a pattern in the sky is known as a ____________ .

(d) A celestial body that revolves around a planet is known as __________.

(e) Shooting stars are actually not ____________.

(f) Asteroids are found between the orbits of _________ and _________ .

5. Mark the following statements as true (T) or false (F):

(a) Pole Star is a member of the solar system. ( )

(b) Mercury is the smallest planet of the solar system. ( )

(c) Uranus is the farthest planet in the solar system. ( )

(d) INSAT is an artificial satellite. ( )

(e) There are nine planets in the solar system. ( )

(f) Constellation Orion can be seen only with a telescope. ( )

6. In which part of the sky can you find Venus if it is visible as an evening star?

7. Name the largest planet of the solar system.

8. What is a constellation? Name any two constellations.

9. Draw sketches to show the relative positions of prominent stars in

(a) Ursa Major and (b) Orion

10. Name two objects other than planets which are members of the solar system.

11. Explain how you can locate the Pole Star with the help of Ursa Major.

12. Do all the stars in the sky move? Explain.

13. Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?

14. The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accomodate?

Please refer to attached file for NCERT Class 8 Science Stars And The Solar System