Keeping Time with the Skies – NCERT Solutions for Class 8 Science (2025–26)

1. State whether the following statements are True or False.

1. We can only see that part of the Moon which reflects sunlight towards us.
2. The shadow of Earth blocks sunlight from reaching the Moon causing phases.
3. Calendars are based on various astronomical cycles which repeat in a predictable manner.
4. The Moon can only be seen at night.

• Answer:
• 1. True
• 2. False
• 3. True
• 4. False

2. Amol was born on 6th of May on a full Moon day. Does his birthday fall on the full Moon day every year? Explain.

Answer: No, Amol’s birthday will not fall on a full Moon day every year because the date of the full Moon changes each year based on the lunar calendar, while his birthday is fixed as per the solar (Gregorian) calendar. The two cycles do not match exactly in length.

3. Name two things that are incorrect in Fig. 11.10.

Answer:

• The illuminated part of the Moon is not facing the Sun (in the illustration).
• The sequence of phases shown is not as per the actual lunar cycle.

4. Look at the pictures of the Moon in Fig. 11.11, and answer:

1. Write the correct panel number for the phases:
   • Picture label (A–F) | Phase of Moon
2. List picture labels of the phases of the Moon never seen from Earth.

Answer:

• (i) The correct panel number depends on the actual images provided in Fig. 11.11. (Refer to textbook for exact mapping.)
• (ii) The phases showing the far side of the Moon (not illuminated as seen from Earth) are never visible from Earth.

5. Malini saw the Moon overhead in the sky at sunset.

1. Draw the phase.
2. Is the Moon waxing or waning?

Answer:

• (i) The phase is exactly half (the first quarter or waxing phase), so it would look like a half-moon (right side bright for waxing in Northern Hemisphere).
• (ii) The Moon is waxing.

6. Ravi saw a crescent Moon, rising in the East as the Sun was setting. Kaushalya saw a gibbous Moon during the afternoon in the East. Who is correct?

Answer: Kaushalya is correct. A gibbous Moon is visible in the afternoon rising in the East, while a crescent Moon is seen before sunrise or after sunset, but not usually rising at sunset.

7. Scientific studies show the Moon is getting farther away and slower in its revolution. Will luni-solar calendars need an intercalary month more often or less often?

Answer: Luni-solar calendars will need an intercalary (extra) month less often, because the lunar months will get longer, and fewer extra months will be needed to keep the calendar in sync with the solar year.

8. In 3 years, 37 full Moons occur in a solar calendar. Show that at least two full moons must happen in the same month of the solar calendar.

Answer: There are 36 months in 3 years. With 37 full Moons, by the pigeonhole principle, at least one month will have two full Moons, since the number of full Moons exceeds the number of months.

9. Vaishali saw the Moon from sunset to sunrise. Which phase would she have noticed?

Answer: She would have noticed the full Moon phase, as only the full Moon rises at sunset and sets at sunrise, remaining visible throughout the night.

10. If we stopped having leap years, in approximately how many years would Indian Independence day occur in winter?

Answer: The calendar would shift about 1 day every 4 years. To shift from 15 August (monsoon) to winter (around mid-January), which is approximately 153 days, it would take 153 × 4 = 612 years.

11. What is the purpose of launching artificial satellites?

Answer: Artificial satellites are launched for purposes such as weather forecasting, telecommunications, earth observation, scientific research, navigation, remote sensing, and exploring outer space.

12. On which periodic phenomenon are (i) day (ii) month (iii) year based?

• Answer:
• Day: Rotation of the Earth on its axis
• Month: Revolution of the Moon around the Earth (lunar phases)
• Year: Revolution of the Earth around the Sun

NCERT Solutions for Class 8 Science Chapter 11: Keeping Time with the Skies (2025-26)

Understanding phases of the Moon, the origin of calendars, and the role of artificial satellites is essential for Class 8 Science Chapter 11. With structured learning, you can master these key astronomical concepts for exams and real-life observations.

This chapter builds your foundation in understanding time, months, and years through natural phenomena. Regular practice of Class 8 Science NCERT solutions helps you clarify doubts and boost your confidence for the Science 2025-26 exam.

Review important sections like lunar phases and calendar systems to improve your retention. Consistent revision using exercise-based learning will enhance your performance in school assessments and deepen your scientific understanding.