STD-5, CHAPTER-12, OBSERVING THE SKY, EXTRA QUESTION ANSWERS

1.      The sun rises in the _____.

Ans: East

2.      The sun sets in the _____.

Ans: West

3.      State the cause of the apparent motion of the sun from east to west?

Ans: As the earth rotates from west to east, the sun appears to move from east to west.

4.      Name the morning star.

Ans: Mercury or venus

5.      Name the evening star.

Ans: Mercury or venus

6.      In which part of the sky are we likely to find Venus when it is visible as an evening star?

Ans: Venus is seen very low near the horizon in the sky.

7.      Name the brightest and most recognisable object in the night sky.

Ans: The moon is the brightest and most recognisable object in the night sky.

8.      Name the brightest object in the sky after the sun and the moon.

Ans: Venus is the brightest object in the sky after the sun and the moon.

9.      Name the planets which can be seen in the night sky even with the unaided eye.

Ans: Mars, venus, Jupiter and Saturn are the planets that can be seen in the night sky even with the unaided eye.

10.  Why cannot we see Uranus and Neptune with unaided eye?

Ans: We cannot see Uranus and Neptune with unaided eye, because they are very faint.

11.  Name the first planet discovered by using a telescope.

Ans: Saturn was the first planet discovered by using a telescope.

12.  How can we know about the temperature of stars from their colours?

Ans: The hottest stars shine with a whitish-blue light.

The other stars shine with a yellowish white light.

13.  The sun shines with a ______ light.

Ans: Yellowish-white light.

14.  Name the star nearest to the Earth.

Ans: The nearest star to the Earth is the Sun.

15.  Why do stars appear as points to us?

Ans: Stars appear as dim points in the night sky. This is due to their very large distances from us.

16.  Why the sun appears like a ball, while other stars appear points to us?

Ans: Almost all the stars are million of times farther away from us as compared to the distance of the sun from us. It is for this reason that the sun appears like a ball to us, but the other stars appear only as points or dots.

17.  Why do, we usually not see the stars during the day?

Ans: The stars are not visible during day-time due to sun’s brightness.

18.  Define the term ‘constellation’.

Ans: A constellation is a group of stars that appear to form some recognisable pattern or shape in the sky.

19.  Why was the concept of constellations important?

Ans: The concept of constellations was important as ancient people were dependent on these stars to find directions and to measure time.

20.  Name some constellations.

Ans: Some constellations are, Ursa Major (Big Dipper), Orion, Ursa Minor (Small Dipper) and Cassiopeia.

21.   Give a short description about Ursa Major.

Ans: i) Ursa Major is seen during the spring, in the early part of night.

ii) Ursa Major is also known as the Great Bear (or Big Dipper).

iii) There are seven prominent stars in Ursa Major.

iv) The two stars, at the top of this constellation, help to locate the Pole Star.

22.  How can we locate the Pole Star with the help of Ursa Major?

Ans: The two stars, at the top of Ursa Major, are called pointers. The line joining those points directs the position of the Pole star (North Star).

23.  In what respects is, the pole star, different from other stars?

Ans:i) The pole star, unlike other stars, appears to remain fixed at one place.

ii) This is so because it lies along the axis of rotation of the earth.

iii) Because of this special feature, this star has been useful to travellers. It defines the North direction.

24.  Write the difference between a planet and a star.

Ans:i) Planets appear like tiny discs whereas stars appear as points.

ii) Stars appear to twinkle. Planets do not twinkle.

iii) Stars appear to be almost stationary. Planets change their relative position with respect to each other.

25.  Planets appear as tiny discs whereas stars appear as points. Why?

Ans: A planet is closer to us than the stars. That is why, planets appear like tiny discs whereas stars appear as points.

26.  Why planets (wandering stars) are so named?

Ans: i) Planets change their relative position with respect to each other.

ii) They appear to move against the background of stationary stars.

iii) This was the reason why ancient people named them as planets i.e. wandering stars.

27.  A star appear to rise four minutes earlier every day. Give reason.

Ans: i) The earth revolves around the sun.

ii) Alongwith this revolution around the sun, the earth also rotates about its own axis.

iii) These two motions of the earth cause the same star to appear to rise four minutes earlier every day.

28.  We see a whole different set of stars in the sky after every six months. Give reason.

Ans: The earth revolves around the sun and, in six months time, moves to the other side of the sun. Therefore, we see a whole different set of stars in the sky after every six months.