Question Bank — Keeping Time with the Skies

NCERT Class 8 Science · Chapter 11 · CBSE Board Pattern

Class 8 Science Chapter 11 Question Bank CBSE Board Pattern

QUESTION BANK

Class VIII Science – Chapter 11: Keeping Time with the Skies
(Based strictly on NCERT text – fresh questions)

Section A — MCQs (1 mark each)

1. The changing shapes of the bright portion of the Moon as seen from the Earth are called
(a) eclipses (b) phases of the Moon (c) lunar months (d) solar days

2. On a full Moon day, the Moon is seen nearly
(a) in the same direction as the Sun (b) opposite the Sun (c) very close to the Sun (d) at the zenith at sunrise

3. Which of the following is the correct reason for the phases of the Moon?
(a) The Moon changes its shape every month.
(b) Earth’s shadow falls on the Moon.
(c) Different portions of the illuminated half of the Moon face the Earth as it revolves.
(d) The Moon emits its own light at different times.

4. A waxing Moon is easiest to observe at
(a) sunrise (b) sunset (c) midnight (d) noon

5. The Indian National Calendar is a
(a) purely lunar calendar (b) purely solar calendar (c) luni-solar calendar (d) sidereal calendar only

6. Assertion (A): We cannot see the Moon on a new Moon day.
Reason (R): On a new Moon day, the non-illuminated portion of the Moon faces the Earth.

7. Assertion (A): Festivals like Eid-ul-Fitr keep shifting earlier in the Gregorian calendar every year.
Reason (R): Purely lunar calendars do not add an intercalary month to match the solar year.

8. The cycle from one full Moon to the next takes approximately
(a) 24 hours (b) 29.5 days (c) 365 days (d) 50 minutes

9. Artificial satellites appear in the night sky as
(a) fixed stars (b) fast-moving points of light (c) flashing coloured lights (d) stationary bright objects

10. In the Gregorian calendar, an extra day is added every four years to
(a) match the Moon’s phases (b) keep the calendar in step with seasons (c) celebrate leap year festivals (d) adjust for the Moon’s revolution

Section B — Very Short Answer (2 marks each)

11. Why does the position of the Moon at sunrise appear shifted on successive days?

12. State two differences between the waning and waxing periods of the Moon.

13. What is the difference between a mean solar day and a lunar month?

14. Why do some Indian calendars add an Adhika Maasa every 2–3 years?

15. Name the two Indian luni-solar calendars on the basis of the start of the month (Amant and Purnimant).

16. How do artificial satellites help in disaster management? Give one example from the chapter.

Section C — Short Answer (3 marks each)

17. Using the ball-and-torch activity described in the chapter, explain why the line separating the illuminated and non-illuminated portions of the ball appears curved at certain positions.

18. Draw a simple labelled diagram showing the positions of the Sun, Earth and Moon on a full Moon day and on a new Moon day. Mark the illuminated and non-illuminated halves.

19. Explain why the same phase of the Moon is visible to people living on different parts of the Earth on any given day.

20. Differentiate between a solar calendar and a luni-solar calendar with one example of each used in India.

21. Why does the Moon rise about 50 minutes later each day? Explain with reference to the Earth’s rotation and the Moon’s revolution.

Section D — Long Answer (5 marks each)

22. Describe an activity to measure the duration of a solar day using a stick and its shadow. Draw a labelled diagram of the setup and explain how the shortest shadow helps identify the time when the Sun is at its highest point. (Diagram required)

23. “The phases of the Moon are caused by the revolution of the Moon around the Earth and not by the shadow of the Earth.” Justify this statement with the help of a labelled diagram showing at least four positions of the Moon in its orbit and the phases seen from the Earth. (Diagram required)

24. A luni-solar calendar has 354 days while a solar year has nearly 365 days. Calculate:
(a) the difference in days per year,
(b) after how many years the difference becomes nearly one month (30 days),
(c) why an intercalary month is added every 2–3 years. Show all steps.

Section E — Case/Source-Based (4 marks each)

Case 1

Ravi observed the Moon for 15 days starting from a full Moon day. He noted that the bright portion decreased daily and the Moon appeared closer to the Sun each morning. After 15 days he could not see the Moon at sunrise. He then observed it at sunset for the next 15 days.

(i) Name the period Ravi observed in the first 15 days and the next 15 days.
(ii) On which day of his observation would he have seen the crescent Moon?
(iii) Why did the Moon appear closer to the Sun each day in the first 15 days?
(iv) If Ravi continues the activity, after how many days approximately will he see the next full Moon?

Case 2

Meera read that many Indian festivals are linked to the phases of the Moon. Diwali falls on the new Moon of Kartika while Holi falls on the full Moon of Phalguna. She noticed that these dates keep changing in the Gregorian calendar but the shift is usually less than a month.

(i) Which type of calendar (lunar / solar / luni-solar) is used for these festivals?
(ii) Why do the Gregorian dates of Diwali and Holi change every year?
(iii) What adjustment is made in luni-solar calendars to keep festivals roughly aligned with seasons?
(iv) Name one festival that follows a solar sidereal calendar and therefore occurs on nearly the same Gregorian date every year.

Section F — HOTS and Application (3 marks each)

25. Predict-and-justify: What would happen to the visibility of Moon phases if the Moon did not revolve around the Earth but stayed at one fixed position? Justify your answer.

26. Analyse: In Activity 11.1, a student records that on Day 8 after full Moon the bright portion is decreasing but on Day 9 it suddenly appears larger. What could be the possible reason for this anomalous observation?

27. Apply to real-life: A farmer in Rajasthan wants to know the best time to look for the Moon to plan night irrigation. Using the concepts of waxing and waning phases, advise him when and in which direction he should look for the Moon on different days of the lunar cycle.

28. Compare and justify: Situation X – A purely lunar calendar is followed. Situation Y – A luni-solar calendar is followed. In which situation will the seasons remain synchronised with the months for a longer period? Justify with reasoning.

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Section A

  1. (b)
  2. (b)
  3. (c)
  4. (b)
  5. (b)
  6. Both A and R true; R explains A (1 mark)
  7. Both A and R true; R explains A (1 mark)
  8. (b)
  9. (b)
  10. (b)

Section B

  1. Moon moves ahead in orbit while Earth rotates once (1); Earth needs extra rotation to bring Moon to same sky position (1).
  2. Any two valid differences: bright portion increasing/decreasing, Krishna Paksha/Shukla Paksha, seen at sunrise/sunset (1+1).
  3. Mean solar day = 24 h (Earth’s rotation); lunar month ≈ 29.5 days (Moon’s phases) (1+1).
  4. To keep lunar months aligned with seasons (2).
  5. Amant (new Moon start), Purnimant (full Moon start) (1+1).
  6. Communication/weather monitoring/disaster images (any one with example) (2).

Section C

  1. Curved terminator seen when ball/Moon is at intermediate positions (1); only part of illuminated half faces observer (1); matches actual Moon observation (1).
  2. Correct diagram with Sun–Earth–Moon alignment for full Moon (opposite) and new Moon (same side) + labels (3).
  3. Earth’s rotation period (1 day) much shorter than Moon’s revolution (1 month) (1); all observers see nearly same relative position (2).
  4. Solar: follows seasons/365 days (Gregorian/Indian National) (1½); Luni-solar: Moon phases + intercalary month (1½).
  5. Moon revolves a little every day (1); Earth must rotate extra ~50 min to bring Moon overhead again (2).

Section D

  1. Setup diagram with vertical stick + shadow dots (2); shortest shadow marks highest Sun position (2); difference between consecutive days gives solar day duration (1).
  2. Diagram with 4–6 positions (A–H) showing illuminated half and visible portion from Earth (2); correct explanation that phases are due to changing orientation, not Earth’s shadow (3).
  3. (a) 11 days (1); (b) ≈ 2.7 years ≈ 2–3 years (2); (c) accumulated difference reaches one month, so Adhika Maasa added (2).

Section E

Case 1: (i) Waning (Krishna Paksha), waxing (Shukla Paksha) (1); (ii) around Day 11–12 after full Moon (1); (iii) Moon moves closer to Sun in sky as it revolves (1); (iv) ≈ 29–30 days (1).
Case 2: (i) Luni-solar (1); (ii) lunar year shorter than solar year (1); (iii) intercalary/Adhika Maasa added every 2–3 years (1); (iv) Makar Sankranti / Pongal / Bihu etc. (1).

Section F

  1. Phases would disappear / Moon would appear same shape daily (1); no change in relative orientation of Sun–Moon–Earth (2).
  2. Possible error in recording date/time, cloud cover, or wrong identification of day (any logical reason with reference to activity) (3).
  3. Waxing Moon – look west at sunset (1); waning Moon – look east at sunrise (1); crescent/gibbous accordingly (1).
  4. Situation Y (luni-solar) (1); intercalary month keeps lunar months aligned with seasons (2).
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All questions are answerable from the NCERT chapter text. Reviewed by GFIS faculty.