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

Start by reviewing these Class 8 Science Curiosity Solutions Chapter 11 Keeping Time with the Skies Question Answer to strengthen your knowledge.

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 (InText)

Question 1.
Have you ever seen the Moon during the day? Why do you think it is sometimes visible when the Sun is up? (Page 170)
Answer:
Yes, the Moon can be seen during the day because it reflects sunlight and can be bright enough to be visible against the blue sky. Its visibility depends on its position relative to the Sun and Earth.

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:
On the Moon, one day (from sunrise to the next sunrise) would be about 29.5 Earth days. A month would be the time taken for one full rotation and revolution (same 29.5 Earth days), while a year would still be the time taken by the Earth to orbit the Sun about 365 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, we would see two bright objects in the sky with different phases. Their combined gravity would affect tides more strongly, and the night sky would look brighter and more dynamic.

Question 4.
If we didn’t have clocks or calendars, how else could we measure time? (Page 170)
Answer:
We could measure time using natural events like the position of the Sun (shadows), the phases of the Moon, the rising and setting of stars, or seasonal changes.

Question 5.
Why does the illuminated portion of the Moon seen from the Earth decrease when it appears closer to the Sun ? (Page 174)
Answer:
The illuminated portion of the Moon seen from Earth decreases when it appears closer to the Sun because of the changing positions of the Sun, Earth and Moon. As the Moon moves closer to the Sun in the sky (near the new Moon phase), the sunlit side of the Moon faces away from us, and we can only see a small part of its illuminated surface. This makes the visible bright portion appear smaller, resulting in waning phases.

Question 6.
Why do most Indian festivals fall on different dates every year? (Page 183)
Answer:
Most Indian festivals are based on the lunar calendar, which is about 11 days shorter than the solar year. This difference causes the festival dates to shift each year when compared to the Gregorian calendar.

Question 7.
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:
Those “moving stars” are satellites. Yes, their motion is periodic because they orbit Earth at regular intervals.

Keeping Time with the Skies Class 8 Questions and Answers (Exercise)

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 in a predictabel manner.
(iv) The Moon can only be seen at night.
Answer:
(i) True We can only see that part of the Moon which reflects sunlight towards us.
(ii) False Phases of the Moon are not caused by Earth’s shadow, but by the changing view of its sunlit part.
(iii) True Calendars are based on various astronomical cycles.
(iv) False The Moon can also be seen during the day.

Question 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 your answer.
Answer:
No, Amol’s birthday will not always fall on a full Moon day because the lunar month (29.5 days) and the solar calendar month do not match. The full Moon day changes each year with respect to calendar dates.

Question 3.
Name two things that are incorrect in figure.

Answer:
The stars are shown in front of the Moon, but stars are always behind the Moon. The Moon is shown as partly covered by clouds and stars, which is unrealistic because stars cannot appear near the bright Moon like that.

Question 4.
Look at the pictures of the Moon in 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 1 or figure on topic 11.1 as reference.
Answer:
(i) Three days after new Moon – C
Full Moon – E
Three days after full Moon – F
A week after Full Moon – A
Day of new Moon – B

(ii) The far side of the Moon (the side not visible from Earth) is never seen, but all the phases shown (A, B, C, D, E, F) represent visible phases. Hence, none of these labels are phases that cannot be seen from Earth.

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) The phase would be full moon
(ii) The Moon is neither waxing nor waning on a full Moon day.

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. A crescent Moon is never seen rising in the East at sunset; it is seen near sunrise or early evening. A gibbous Moon can be seen during the afternoon.

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 more often or less often?
Answer:
More often, because a slower Moon will take longer to complete its phases, increasing the difference between lunar months and the solar year.

Question 8.
A total of 37 full moon happens 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 calender.
Answer:
A year has 12 months × 3 years = 36 months.
There are 37 full Moons in 3 years.
Thus, 37 – 36 = 1 extra full Moon must occur in the same month as another full Moon.
So, at least two full Moons will be in one month.

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:
It must have been a full Moon because only a full Moon rises at sunset and sets at sunrise.

Question 10.
If we stopped having leap years, in approximately how many years would the Indian Independence day happen in winter?
Answer:
The difference between the solar year (365.25 days) and a 365 day calendar is about 0.25 days per year.
To shift by 6 months (≈ 183 days),
183 ÷ 0.25 = 732 years.

Question 11.
What is the purpose of launching artificial statellites?
Answer:
Artificial satellites are launched for purposes like communication, weather forecasting, navigation, research, Earth observation, and scientific experiments.

Question 12.
On which periodic phenomenon are the following measures of time based: (i) day (ii) month (iii) year?
Answer:
Day : Rotation of the Earth on its axis.
Month : Revolution of the Moon around the Earth (phases of Moon).
Year : Revolution of the Earth around the Sun.

Class 8 Science Chapter 11 Question Answer (Activities)

Activity 1 (Page 171)

Aim
To observe and record the changes in the visible portion of the Moon over a month.

Materials Required
Notebook and pencil, calendar, open area to observe the Moon.

Procedure

1. Begin observations on the day after a full Moon.
2. Spot the Moon at sunrise in the western sky as shown in Fig a.
3. Note the date, time and shape of the Moon in your notebook.
4. Shade the bright portion of the Moon in a circle diagram.
5. Repeat the observation daily for 15 days during sunrise and the next 15 days during sunset.
6. Observe whether the bright portion is increasing (waxing) or decreasing (waning).

Observation

1. Date and time of Moon sighting.
2. Sketch of the bright portion (waxing/waning).
3. Note if the Moon appears closer or farther from the Sun.

Conclusion
The Moon’s visible shape changes from full to new and back due to its revolution around Earth, which makes us see different portions of its sunlit half.

Viva Questions

1. Why does the Moon appear to change its shape?
2. What is the time period of the Moon’s revolution around Earth?
3. Which phase of the Moon occurs 15 days after a new Moon?
4. When does the moon appear closer to the Sun in the sky?

Activity 2 (Pages 174 and 175)

Aim
To demonstrate how Moon phases are formed using a ball and a lamp.

Materials Required
Soft ball, stick to hold the ball, torch or lamp, dark open space.

Procedure

1. Insert a stick into the ball to hold it firmly as shown in Fib b.
2. Go to a dark open place or a dark room.
3. Place a lamp or torchlight at about 3 m distance.
4. Hold the ball at arm’s length above your head, facing the lamp.
5. Slowly rotate your body anti-clockwise, keeping the ball towards the lamp.
6. Observe the changing shape of the illuminated part of the ball.

Observation

1. Bright portion of the ball changes shape when rotated.
2. The line separating light and dark portion is curved.

Conclusion
The phases of the Moon are caused by our changing view of its sunlit half as it moves around Earth.

Viva Questions

1. What does the ball represent in this activity?
2. What does the lamp represent?
3. Why does the ball show phases when rotated?
4. Is the dark part of the ball actually dark?
5. Which Moon phase is seen when the ball is fully illuminated?

Activity 3 (Pages 178 and 179)

Aim
To find the time between two consecutive shortest shadows of a stick, i.e., the duration of a solar day.

Materials Required 1 m vertical stick, chalk/markers, watch/clock, open sunny area

Procedure

1. Fix the stick vertically on the ground in an open area as shown in Fig c.
2. Start observing around 11:00 am.
3. Every 10 minutes, mark the tip of the stick’s shadow with chalk.
4. Continue until around 1:10 pm. when the shadow starts increasing again.
5. Identify the time when the shadow was shortest (solar noon).
6. Repeat this for two consecutive days and note the difference in time.

Observation

1. Time at which the shadow is shortest each day.
2. Time difference between two consecutive days (approx. 24 hours).

Conclusion
The duration between two solar noons is about 24 hours, defining a solar day.

Viva Questions

1. Why is the shadow shortest at noon?
2. Why does the length of the shadow change during the day?
3. Which direction does a shadow point at noon?
4. What is solar noon?

Activity 4 (Pages 185 and 186)

Aim
To observe artificial satellites moving across the night sky.

Materials Required
Open sky view, notebook, watch/clock, Binoculars (optional)

Procedure

1. Go to an open area just before sunrise or after sunset.
2. Look for moving points of light in the sky that are not twinkling.
3. Record the time, direction and path of the moving object.
4. Use a mobile app or website to confirm satellite sightings.

Observation

1. Moving point of steady light across the sky.
2. Start and end time, direction of movement.

Conclusion
Satellites are visible as moving bright points because they reflect sunlight, unlike stars which appear stationary.

Viva Questions

1. What is an artificial satellite?.
2. Why are satellites visible after sunset or before sunrise?
3. How can you distinguish a satellite from a star?.
4. Name two Indian satellites.
5. What is space debris?