Keeping Time with the Skies Class 8 Question Answer Science Chapter 11

Go through BSE Odisha Class 8 Science Solutions Chapter 11 Keeping Time with the Skies Question Answer to understand textbook questions more clearly.

Class 8 Science Curiosity Chapter 11 Question Answer

Class 8 Science Ch 11 Keeping Time with the Skies Question Answer

Class 8 Science Chapter 11 Keeping Time with the Skies Question Answer

Probe and Ponder Questions

Question 1.
Have you ever seen the Moon during the day? Why do you think it is sometimes visible when the sun is up?
Answer:
Yes, the Moon can often be seen during the day, especially in its waxing and waning phases. This happens because the Moon reflects sunlight and during certain phases it is high enough in the sky while the Sun is also above the horizon, so the bright part of the Moon is visible to us.

Question 2.
Imagine you lived on the Moon instead of Earth. What would you mean by a day, a month or a year?
Answer:

• A day on the Moon (from one sunrise to the next) would be about 29.5 Earth days.
• A month might be defined by one complete orbit around Earth (which is also about 27.3 Earth days).
• A year is the time the Earth takes to complete one orbit around the Sun, which you could still observed from the Moon in about 365 days.

Question 3.
What would happen if Earth had two moons instead of one? How would that change the night sky?
Answer:
If Earth had two moons:

• The night sky would be brighter and more dynantic.
• There could be more frequent eclipses.
• The gravitational pull on Earth would be different, possibly affecting tides.
• The two moons might cross paths, creating fascinating views or even risks of collision over long periods.

Question 4.
If we didn’t have clocks or calendars, how else could we measure time?
Answer:
We could measure time by:

• Observing the position of the Sun (sunrise, noon, sunset).
• Using the phases of the Moon to count months.
• Tracking stars and constellations that change with the seasons.
• Using natural events, like plant flowering or animal behaviour to mark the passage of time.

Question 5.
Share your questions …………
Answer:
Here are some fun questions from the chapter.

• Why does the Moon change shapes?
• How do festivals link to Moon phases?
• Can we see statellites at night?
• Why do some calendars add extra days?

InText Questions

Question 1.
Why does the illuminated portion of the Moon seen from the Earth decrease when it appears closer to the Sun?(Page 174)
Answer:
The Moon does not have its own light; it shines because it reflects sunlight that falls on it. When the Moon appears closer to the Sun in the sky, the side of the Moon that is illuminated by the Sun faces away from the Earth. As a result, from Earth we can see only a smaller part of the bright portion and most of the Moon’s surface visible to us is dark. That is why the illuminated portion of the Moon seen from Earth decreases when it comes closer to the Sun – it appears as a cresent Moon and finally becomes invisible on the new Moon day.

Question 2.
So, changing phases of the Moon is a natural periodic event, with a cycle of almost a month, which can also be used for time keeping. Yes, along with the natural periodic events of day and night and the changing seasons about which we learnt earlier. But how are these periodic events used for keeping time? (Page 178)
Answer:
The natural periodic events – like day and night, phases of the Moon and changing seasons – helps measure time because they repeat regularly after fixed intervals.

• Day and Night: The rotation of the Earth on its axis causes day and night. One complete rotation takes 24 hours which is used to define one day.
• Phases of the Moon: The Moon revolves around the Earth and completes one full cycle of phases (from one full Moon to the next) in about 29.5 days, which forms the basis of a month.
• Changing Seasons: The Earth revolves around the Sun once in about 365 days. This regular change in the position of the Earth causes seasons and gives us a year.
• Thus, these periodic motions of celestial bodies – the Earth and the Moon acts as natural clocks and calendars that humans have used for keeping time since ancient times.

Question 3.
Why do most Indian festivals fall on different dates every year? (Page 183)
Answer:
Many Indian festivals are linked to the phases of the Moon and hence are based on either lunar or luni-solar calendars, not the regular Gregorian solar calendar that we use daily. A lunar month is about 29.5 days and a lunar year (12 lunar months) has about 354 days, which is 11 days shorter than the solar year of 365 days.

Because of this difference, festivals like Diwali, Holi, Eid-ul-Fitr and Buddha Purnima which follow the Moon’s phases appear on different Gregorian calendar dates each year. To adjust this difference, the luni-solar calendars sometimes add an extra month called Adhika Maasa (extra month) every few years which helps keep the festivals in the same season.

Question 4.
When I look at the night sky in early evening, I see some moving stars. What are they? Is their motion also periodic? (Page 185)
Answer:
The moving ‘stars’ seen in the night sky are actually artificial satellites, not real stars. These are man-made objects launched into space that revolve around the Earth. They reflect sunlight which is why they appear as small moving points of light in the sky. Yes, their motion is periodic. Each satellite orbits the Earth in a fixed path and takes about 100 minutes to complete one round. Artificial satellites are used for communication, weather forecasting, navigation, disaster management and scientific research.

Keeping Time with the Skies Class 8 Questions and Answers

Keep the Curiosity Alive (Pages 187-188)

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 can only see the part of the Moon that reflects sunlight towards Earth.
(ii) False: The Earth’s shadow causes lunar eclipses, not the regular phases of the Moon.
(iii) True: Calendars are based on repeating astronomical events like day-night, Moon phases, and seasons.
(iv) False: The Moon can also be seen during the daytime, depending on its phase and position 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 does not fall on a full Moon Day every year. This is because the Moon’s phases follow a lunar cycle of about 29.5 days, while the calendar year follows the solar cycle of about 365 days. So, the date of the full Moon changes 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 11.1 or Figure as reference.
Answer:
(i)

Picture label	Phase of Moon
C	Three days after New Moon
E	Full Moon
F	Three days after the Full Moon
A	A week after the Full Moon
B	Day of New Moon

(ii) Picture B (New Moon phase) is never seen from Earth because the illuminated side of the Moon is facing 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 overhead only during the first quarter (a week after New Moon), when the right half is illuminated. So, we need to draw a half Moon (right half bright, left half dark).
(ii) Waxing phase (because it occurs after New Moon and the bright part is increasing).

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 telling the truth because gibbous Moons can be seen in the East during the afternoon. Ravi’s statement is incorrect because Crescent Moons do not rise in the East at sunset. A crescent Moon appears just after the New Moon (waxing crescent) or just before the New Moon (waning crescent). Waxing crescent is visible after sunset in the western sky, not rising in the east, and waning crescent rises just before sunrise, not at sunset.

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:
Luni-solar calendars will need an intercalary month more often as the Moon moves farther and slower, and it takes longer to complete a cycle. So, a lunar year becomes even shorter compared to the solar year.

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, at least two full Moons must happen in the same solar month.

• A solar calendar has 12 months × 3 years =36 months.
• 37 full Moons in 36 months, at least one month must have 2 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:
As the Moon is visible all night long only on a Full Moon, it is 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:
One leap year adds ∼1 day every 4 years.
Without leap years, the calendar shifts by 1 day every 4 years.
There are roughly 183 days between 15 August (monsoon) and winter (mid-February).
183 days × 4=732 years
In approximately 730-732 years, 15 August would occur in winter.

Question 11.
What is the purpose of launching artificial satellites?
Answer:
Artificial satellites are launched for:

• Communication
• Navigation
• Weather monitoring -Scientific research
• Disaster management
• Earth observation

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.

Class 8 Science Chapter 11 Question Answer

Activity 1

Activity 1.

Let us explore
Aim: To observe the shape of the moon from full moon day to new moon day.

Procedure:
1. Observe the Moon at sunrise in the western direction starting from the first day after the full Moon.
2. Construct a table same as Table -1 in your notebook. Complete the following details:

• Date
• When you saw the Moon (at sunrise or sunset)?
• Shade the corresponding Circle with pencil to show the bright portion of the Moon as shown in figure.

Table 1: Documenting changes in the Moon’s appearance

Answer:

Observations:

1. From the second day onwards also document the following:

• Is the size of bright portion of the Moon increasing or decreasing from the previous day.
• Yes, there is a change in shape of the moon everyday. Bright portion goes on decreasing.
• Whether the Moon appears closer to or farther from the Sun in the sky than the day before.

2. After about 15 days, you may not be able to see the Moon at sunrise or sunset. For the next 15 days, carry out this activity at sunset.

Inferences:

• Moon appear different each day.
• No, after 15 days, you may not be able to see the moon at sunrise or sunset.
• After the full moon, the bright face of the moon goes on decreasing every night. By another fifteen days again new moon is formed.
• The crescent moon goes on increasing everyday, till on the fifteenth day (from the new moon), the full face of the moon is visible.
• Each morning at sunrise, moon appears closer to the sun’s position in the sky.

Activity 2.

Let us explore
Aim: To show the Moon’s phases with a simple model.
Materials Required: A soft ball, a stick, a torch or lamp as the sun, your own head as the Earth.

Procedure:

• Take a small soft ball and insert a stick into it [(Figure (a)]. This represents the Moon.
• Move to a dark open place (at night), and ask your teacher or guardian to shine a torchlight towards you from about 3 m which will represent that light is coming from the Sun or stand near an electric lamp. Your head represents the Earth.
• Hold the ball in your hand, slightly above your head.
• Shine the torch toward the ball to represent sunlight.
• As you turn in a circle, the ball (“Moon”) shows a changing illuminated portion to your eyes.

Observations:

What does the model show

• Full Moon: When the ball is held opposite the lamp (behind you compared to the Sun), the side facing you is fully lit-just like a full Moon.
• New Moon: When the ball is held between your head and the lamp (towards the Sun), you see only the dark side-like a new Moon.
• Crescent and Gibbous Phases: Turning the ball slowly, the visible portion transitions. Sometimes you see a crescent (less than half lit), other times gibbous (more than half lit).
• The line between the bright and dark parts is always curved-this matches what we see in the real Moon.

Inference:
The Science behind the phasses

• Half illuminated, Half Dark: At every moment, half the Moon is lit by sunlight and half is in darkness.
• Moon’s Revolution: As the Moon revolves around the Earth, the angle between Earth, Moon and Sun changes. The part of the Moon we see as bright changes accordingly.

Activity 3.

Let us measure a day!

Aim: To find the duration of a day by observing the length of the shadow.
Materials Required: A 1m stick.

Procedure:

• Choose a small flat and open area in a ground which receives sunlight during the day. Fix a 1 m stick vertically in it as shown in figure.
• Let us start observing the shadow at 11:00 a.m. Every minute, mark a dot on the ground at the tip of the stick’s shadow. Keep marking dots until around 1:10 p.m.
• Identify when the shadow was shortest and find out its time by counting the number of dots. Record this time in Table. Repeat this experiment for the next few days.
• Now calculate the duration of the solar day. This can be done by finding a difference in time on two consecutive days as shown in Table.

Observations:
Table1: Finding the duration of a solar day

Answer:

Date	Time of shortest shadow (hh:mm)	Duration of day (hh:mm)
22 March 2025 23 March 2025 24 March 2025 25 March 2025 26 March 2025	12:20 12:20 12:19 12:19 12:18	…………… 24:00 23:59 23:59 24:00

1. The shortest shadow during the day marks when the sun is at highest point in the sky (noon).
2. Measuring from one day’s noon to the next day gives the length of a day.
3. The average solar day i.e. average duration of the day is about 24 hours.

Inference:
The Month and the Moon

• The phases of the Moon create another natural cycleone complete phase cycle (from full Moon to next full Moon) takes about 29.5 days (approximately one month).
• This lunar cycle is the basis for measuring a month. (see figure)

The Year and the Seasons

• One year is the duration for Earth to make a full revolution around the Sun, which is about 365 \(\frac{1}{4}\) days.
• The repetition of seasons (spring, summer, autumn, winter) marks the annual cycle.
• The Earth undergoes one cycle of seasons during this time, which can be used to define a solar year (see figure).

Activity 4.

Let us identify
Aim: To observe artificial satellites.
Materials Required: A telescope.

Procedure:

• Go to a location that has a clear view of sky; along with an adult. There should not be any obstruction of trees or tall buildings.
• To identify satellites in the sky, look for a small, bright, continuously moving dot in the sky, typically before sunrise or after sunset.

Observations:

• Can be seen without a telescope or with binoculars.
• Satellite-tracking mobile apps or websites help identify visible satellites in your location and when they will be passing above you in the sky.

Keeping Time with the Skies Class 8 Extra Questions and Answers

Short Answer Type Questions

Question 1.
How does the Moon’s position in the sky change each day?
Answer:
The Moon’s position shifts slightly eastward each day, so it is not in the same place at the same time. This is why its rise and set times also change daily.

Question 2.
Why does the Moon sometimes appear in the daylight?
Answer:
The Moon can rise before sunset, sometimes in the afternoon. In such cases, it is visible in the sky while the Sun is still up.

Question 3.
What does the simple ball-and-lamp model of the Moon help us understand?
Answer:
The model shows how sunlight falls on the Moon and creates different phases. By turning with the ball, we can see changes in the illuminated portion, similar to what happens in reality.

Question 4.
Why is the line between the bright and dark portions of the Moon always curved ?
Answer:
The Moon is spherical, so the dividing line between sunlight and shadow is curved. This curve is visible from Earth during all phases.

Question 5.
Why are Moon phases not caused by Earth’s shadow ?
Answer:
Moon phases happen because we see varying parts of its sunlit side as it orbits. Earth’s shadow only causes a lunar eclipse, which is rare.

Question 6.
Why don’t we have eclipses every full Moon or new Moon?
Answer:
The Moon’s orbit is tilted compared to Earth’s orbit. This tilt means the Sun, Earth and Moon usually don’t line up perfectly.

Long Answer Type Questions

Question 1.
Explain the waxing and waning periods of the Moon and how they form a monthly cycle.
Answer:

• The waxing period is when the bright portion of the Moon increases, starting from the new Moon and becoming full in about two weeks. The waning period is when the bright portion decreases, starting from the full Moon and becoming new Moon in about two weeks.
• Together, waxing and waning make a repeating cycle every month. This cycle takes about 29.5 days from one full Moon to the next.
• These changes occur because of the Moon’s revolution around Earth and the changing angle between the Sun, Earth and Moon.

Question 2.
Explain how the motion of the Sun in the sky helps in measuring a day.
Answer:

• The Sun appears to rise in the east, move across the sky and set in the west because Earth rotates on its axis. The highest position of the Sun in the sky, when shadows are shortest, marks noon.
• The time from one noon to the next is called a mean solar day. This length is about 24 hours, which is the basic unit for measuring time in days. This daily cycle has been used since ancient times to keep track of time.

Case-Study Based Questions

1. Read the following passage carefully and answer the questions that follow :

Anita kept a Moon observation diary for a week. On Day 1, she saw a thin crescent on the right side. By Day 4, half of the Moon was visible. By Day 7, almost the full Moon was visible.

(a) Which phase did Anita observe on Day 1?
Answer:
Waxing Crescent

(b) What is the name of the phase on Day 4?
Answer:
First Quarter

(c) Was the Moon waxing or waning during these days?
Answer:
Waxing

Picture Based Questions

I. Look at the pictures and answer the following questions:

(a) Identify the pictures (i) and (ii).
Answer:
(i) Warli painting
(ii) Dhokra Brass Sculpture

(b) Write the name of painting given below and the state from given where it is associated ?
Answer:

Madhubani painting. It is a famous painting associated to Bihar.

Keeping Time with the Skies Class 8 MCQ

Multiple Choice Questions (Mcqs)

Question 1.
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 the Moon’s surface.
(d) The thickness of the Moon’s atmosphere is not constant.
Answer:
(a) We can see only that part of the Moon which reflects light towards us.

Question 2.
What do they call the Moon when it’s more than half lit but not full ?
(a) Crescent
(b) Gibbous
(c) Quarter
(d) Eclipse Moon
Answer:
(b) Gibbous

Question 3.
What is the sequence of phases starting from New Moon?
(a) New Moon → Full Moon → Waxing → Crescent → First quarter
(b) New Moon → Waxing Crescent → First Quarter → Full Moon
(c) Full Moon → Waxing Gibbous → New Moon
(d) First quarter → Full Moon → New Moon
Answer:
(b) New Moon → Waxing Crescent → First Quarter → Full Moon

Question 4.
What causes the phases of the Moon ?
(a) The Earth’s rotation
(b) The Moon’s rotation
(c) The Moon’s orbit around the Earth
(d) The Sun’s movement
Answer:
(c) The Moon’s orbit around the Earth

Question 5.
How long does one complete cycle of Moon phases take?
(a) 7 days
(b) 15 days
(c) 29.5 days
(d) 365 days
Answer:
(c) 29.5 days

Assertion and Reasoning

These questions consist of two statements, each printed as Assertion (A) and Reason (R). While answering these questions, you are required to choose any one of the following four responses.

(a) Assertion (A) and Reason (R) both are correct and reason is correct explanation for assertion.
(b) Assertion (A) and Reason (R) both are correct and reason is not correct explanation for assertion.
(c) Assertion (A) is correct but the Reason (R) is wrong.
(d) Assertion (A) is wrong but the Reason (R) is correct.

1. Assertion (A): The Moon appears to change shape throughout the month.
Reason (R): The Earth casts different shadows on the Moon each night.
Answer:
(c) Assertion (A) is correct but the Reason (R) is wrong.

2. Assertion (A): The full Moon rises at sunset and sets at sunrise.
Reason (R): The full Moon is directly opposite the sun in the sky.
Answer:
(a) Assertion (A) and Reason (R) both are correct and reason is correct explanation for assertion.

Fill in the blanks

1. The Moon does not have its own light, it………… the sunlight.
Answer:
reflects

2. The changing shapes of the Moon that we see from Earth are called ………….
Answer:
Phases

3. A full cycle of the Moon’s phases takes about ……….. days.
Answer:
29.5

4. Waxing Moon is best seen at ………….
Answer:
Sunset

5. Waning Moon is best seen at ………….
Answer:
sunrise.

True or False

1. A lunar eclipse occurs when the Moon comes between the Earth and the Sun.
Answer:
False

2. The Full Moon appears once every lunar cycle.
Answer:
True

3. A Moon’s surface is smooth and shiny.
Answer:
False

4. We can sometimes see the Moon during the daytime.
Answer:
True

5. The Moon always shows the same side to the Earth.
Answer:
True