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

Keeping Time with the Skies Class 8 Question Answer (InText)

Question 1. Have you ever seen the Moon during the day? Why do you think it is sometimes possible when the Sun is up? (Page 170)

Answer: Yes, the Moon is often visible during the daytime, particularly during its waxing and waning phases. It appears because it reflects sunlight, and at certain points in its orbit, it is positioned high in the sky while the Sun is also above the horizon, allowing us to see it clearly even in daylight.

Question 2. Imagine you lived on the Moon instead of Earth. What would you mean by a day, a month, or a year? (Page 170)

Answer:

A single day on the Moon—from one sunrise to the next—lasts about 29.5 Earth days.

A lunar month could be defined as one full orbit of the Moon around Earth, which takes about 27.3 Earth days.

A year, based on Earth’s orbit around the Sun, would still be observed from the Moon as roughly 365 Earth days.

Question 3. What would happen if Earth had two moons instead of one? How would that change the night sky? (Page 170)

Answer: If Earth had two moons:

• Nights would be brighter, with a constantly changing sky.

• Eclipses could occur more often.

• The combined gravitational pull could alter tides and might even influence weather patterns.

• The moons’ orbits might occasionally bring them close to each other, creating striking views and, over long periods, a potential risk of collision

Question 4. If we didn’t have clocks or calendars, how else could we measure time? (Page 170)

Answer: 

Time could be measured by:

• Watching the Sun’s movement—sunrise, midday, and sunset.

• Using the changing phases of the Moon to mark months.

• Noting the seasonal appearance and position of stars and constellations.

• Observing natural cues, such as when plants bloom or how animals behave, to track longer intervals of time.

Keep the Curiosity Alive (Pages 187-189)

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

(i) We can only see that part of the Moon which reflects sunlight towards us.
(ii) The shadow of Earth blocks sunlight from reaching the Moon, causing phases.
(iii) Calendars are based on various astronomical cycles which repeat predictably.
(iv) The Moon can only be seen at night.

Answer:

(i) True: We see only the portion of the Moon that reflects sunlight toward Earth.

(ii) False: The Moon’s phases are not caused by Earth’s shadow; only lunar eclipses occur due to Earth’s shadow.

(iii) True: Calendars are built on recurring astronomical patterns such as the day–night cycle, lunar phases, and seasonal changes.

(iv) False: The Moon is sometimes visible during the day, depending on its phase and location in the sky.

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

Answer: No, Amol’s birthday will not always coincide with a full Moon day. The Moon’s phases repeat every 29.5 days, while the calendar year is based on a 365-day solar cycle. As a result, the full Moon date shifts each year in the Gregorian calendar.

Question 3. Name two things that are incorrect in the Figure.

Answer:
Two incorrect things are:

• Stars are shown near the Moon during the daytime, which is incorrect because stars are not visible in the daytime sky.

• The Moon’s dark part is shaded incorrectly to show a phase. The shadow in the figure suggests it’s caused by Earth’s shadow, which is not true for regular Moon phases; they are caused by the Moon’s position relative to the Earth and Sun, not a shadow.

Question 4. Look at the pictures of the Moon in the figure, and answer the following questions.

(i) Write the correct panel number corresponding to the phases of the Moon shown in the pictures above.

(ii) List the picture labels of the phases of the Moon that are never seen from Earth.
[Hint: You can use your observations from Activity Fig. as a reference.]
Answer:
(i)

(ii) Picture B, which shows the New Moon phase, is never visible from Earth because the lit side of the Moon faces away from us.

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

(i) Draw the phase of the Moon that Malini saw.

(ii) Is the Moon in the waxing or the waning phase?

Answer:

(i) At sunset, the Moon is directly overhead only during the first quarter phase, which occurs about a week after the New Moon. In this phase, the right half of the Moon is lit. Therefore, the correct drawing should show the right half illuminated and the left half in shadow.

(ii) The Moon is in its waxing phase, as this comes after the New Moon and the illuminated portion is growing.

Question 6. Ravi said, “I saw a crescent Moon, and it was rising in the East when the Sun was setting.” Kaushalya said, “Once I saw the gibbous Moon during the afternoon in the East.” Who out of the two is telling the truth?

Answer: Kaushalya is correct because gibbous Moons can indeed be seen in the eastern sky during the afternoon. Ravi is wrong since crescent Moons do not rise in the east at sunset. A waxing crescent appears shortly after sunset in the western sky, while a waning crescent rises just before sunrise—neither occurs at sunset in the east.

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

Answer:  As the Moon gradually moves farther away and its orbital speed decreases, it takes longer to complete a cycle. This makes the lunar year even shorter than the solar year, causing luni-solar calendars to require an extra, intercalary month more frequently.

Question 8. A total of 37 full Moons happen during 3 years in a solar calendar. Show that at least two of the 37 full moons must happen during the same month of the solar calendar.

Answer: Yes, there must be at least two full Moons in the same solar month.

In three years, a solar calendar has 36 months, but there are 37 full Moons in this period. Since 37 full Moons cannot fit into 36 separate months, at least one month will contain two full Moons.

Question 9. On a particular night, Vaishali saw the Moon in the sky from sunset to sunrise. What phase of the Moon would she have noticed?

Answer: Since the Moon remains visible throughout the entire night only during the Full Moon phase, it must be a Full Moon.

Question 10. If we stopped having leap years, in approximately how many years would the Indian Independence Day happen in winter?

Answer: 

A leap year adds about one extra day every four years.

Without these leap years, the calendar would drift by one day every four years.

There are about 183 days between 15 August (monsoon season) and mid-February (winter).

183 days × 4 ≈ 732 years.

So, in roughly 730–732 years, 15 August would shift into the winter season.

Question 11. What is the purpose of launching artificial satellites?

Answer: 

Artificial satellites are used for:

• Communication

• Navigation

• Weather forecasting

• Scientific studies

• Disaster management

• Observing and monitoring Earth

Question 12. On which periodic phenomenon are the following measures of time based:

(i) day

(ii) month

(iii) year?

Answer:

(i) Day → Earth’s rotation

(ii) Month → Moon’s revolution (phases of the Moon)

(iii) Year → Earth’s revolution around the Sun.

Activity 11.1: Let us Explore (Pages 171-172)

Documenting Changes in the Moon’s Appearance

Analysis Questions:

Question 1. Did the Moon appear different each day?

Answer: Yes, its appearance or phase changed from day to day.

Question 2. Was the Moon visible on all days?

Answer: Yes, on those three days, it could be seen at sunrise.

Question 3. Did the Moon appear at the same position in the sky as on the previous day?

Answer: No, each day it appeared nearer to the Sun and lower in the sky.

Activity 11.2: Let us Measure a Day! (Pages 178-179)

Find the average duration of the day. Is it nearly equal to 24 hours?

Answer:

o find the average of 24:00 and 23:59:

1. Convert both to minutes:

• 24:00 = 1440 minutes

• 23:59 = 1439 minutes

2. Add them: 1440 + 1439 = 2879 minutes

3. Divide by 2: 2879 ÷ 2 = 1439.5 minutes

4. Convert back to hours:
   1439.5 minutes = 23 hours 59 minutes 30 seconds

So, the average length of the day is 23 hours 59 minutes 30 seconds, which is almost exactly 24 hours.

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.