CBSE Class 8 Science Chapter 11 Keeping Time With The Skies MCQs Set 03

Science Objective Questions and Answers: Chapter 11 Keeping Time With The Skies

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Question: When the Moon moves ahead in its orbit while Earth completes one rotation, why does the Moon appear roughly 50 minutes later in the sky on the next day when observed at the same time?
A. The Moon's orbital speed is faster than Earth's rotation speed
B. Earth must rotate additional degrees beyond one complete rotation before the Moon returns to nearly the same position in the sky
C. The Moon's gravity slows Earth's rotation slightly each day
D. Atmospheric refraction shifts the Moon's apparent position westward
Show Answer & Explanation

Answer: (B) Earth must rotate additional degrees beyond one complete rotation before the Moon returns to nearly the same position in the sky

Explanation:
As shown in Fig. 11.6, while Earth rotates once in 24 hours returning a viewer to the same location, the Moon has moved further along its orbit. For the Moon to appear in roughly the same spot, Earth needs to rotate somewhat more, which takes an extra 50 minutes.

Question: According to Activity 11.1, which pair of observations together indicates when the Moon is at its closest position to the Sun in the sky?
A. The bright portion increases and the Moon appears at sunrise
B. The bright portion decreases to a crescent and the Moon appears closer to the Sun
C. The bright portion reaches full circle and the Moon is visible all night
D. The Moon cannot be seen because it has moved directly overhead
Show Answer & Explanation

Answer: (B) The bright portion decreases to a crescent and the Moon appears closer to the Sun

Explanation:
The chapter describes that as the Moon's illuminated portion shrinks after a full Moon day, the Moon appears closer and closer to the Sun in the sky, finally appearing as a crescent just before the new Moon day when it is closest to the Sun.

Question: In Activity 11.2, the ball-and-stick simulation represents which concept that helps explain why the Moon's appearance changes?
A. How Earth's shadow causes lunar eclipses
B. The changing visibility of the illuminated half of the Moon as the observer's viewpoint shifts relative to the light source
C. Why the Moon revolves around Earth in an elliptical rather than circular orbit
D. How the Moon's rotation causes different features to face toward Earth
Show Answer & Explanation

Answer: (B) The changing visibility of the illuminated half of the Moon as the observer's viewpoint shifts relative to the light source

Explanation:
Activity 11.2 directly models how the fraction of the illuminated portion visible from the observer's position changes as the ball moves to different positions relative to the lamp, mirroring how different Moon phases appear from Earth as the Moon orbits.

Question: Based on the chapter's explanation of solar calendars, the Gregorian calendar adds a leap day every four years primarily to address which astronomical fact?
A. Earth's orbital speed varies seasonally
B. The Moon's orbit gradually moves farther from Earth
C. Earth takes approximately 365.25 days to orbit the Sun rather than exactly 365 days
D. The tilt of Earth's axis causes seasonal variations in day length
Show Answer & Explanation

Answer: (C) Earth takes approximately 365.25 days to orbit the Sun rather than exactly 365 days

Explanation:
The chapter states that Earth takes nearly an extra quarter of a day (0.25 days) to complete one revolution, and these fractional days accumulate to roughly one full day every four years, requiring the leap year adjustment.

Question: Which astronomical observation described in the chapter most directly proves that the Moon does not emit its own light but reflects sunlight?
A. The Moon is visible during the day
B. Only the side facing the Sun is illuminated, and we can only see the illuminated portion facing Earth
C. The Moon passes through different phases in a predictable monthly cycle
D. The Moon rises and sets at different times each day
Show Answer & Explanation

Answer: (B) Only the side facing the Sun is illuminated, and we can only see the illuminated portion facing Earth

Explanation:
The chapter emphasizes that half the Moon always faces the Sun and becomes illuminated, while the other half remains non-illuminated. We can only observe the illuminated portion of the side facing us, directly demonstrating that the Moon reflects sunlight rather than producing its own light.

Question: In the context of the chapter's discussion of calendars and the Indian National Calendar, why does the new year begin on 22 March rather than any other date?
A. This date marks the moment when Earth reaches its closest point to the Sun
B. This date is the day after the spring equinox, when day and night are roughly equal length
C. This date was chosen arbitrarily by the Calendar Reform Committee in 1952
D. This date ensures the calendar aligns with the sidereal year used by ancient astronomers
Show Answer & Explanation

Answer: (B) This date is the day after the spring equinox, when day and night are roughly equal length

Explanation:
The chapter states that 22 March is the day after the spring equinox, and the Indian National Calendar is based on the tropical year, which is tied to the seasonal cycle beginning at this astronomical event.

Question: According to the chapter, if a person observed the Moon overhead at sunset, which of the following describes the Moon's phase and position in its cycle?
A. Full Moon in the waxing phase
B. Half-illuminated Moon in the waning phase, roughly halfway between full and new Moon
C. Crescent Moon in the waxing phase
D. New Moon invisible except for the thin crescent
Show Answer & Explanation

Answer: (B) Half-illuminated Moon in the waning phase, roughly halfway between full and new Moon

Explanation:
• When Moon is overhead at sunset, it is near the first quarter position
• At this position, half of the illuminated portion faces Earth
• The Moon is in the waning phase after passing full Moon
• The Moon appears roughly 90 degrees away from the Sun in the sky

Question: The chapter describes luni-solar calendars adding an intercalary month (Adhika Maasa). What problem does this practice solve?
A. It ensures that lunar months align with weeks
B. It prevents the 354-day lunar year from drifting away from the 365-day seasonal cycle
C. It corrects for the Moon's orbit becoming more elliptical over time
D. It maintains the same number of Sundays throughout each month
Show Answer & Explanation

Answer: (B) It prevents the 354-day lunar year from drifting away from the 365-day seasonal cycle

Explanation:
Lunar months total only 354 days per year, falling short of the solar seasonal year by roughly 11 days. Without adjustment, seasons would gradually shift away from the same months year after year. Adding an extra month every few years brings the lunar and seasonal cycles back into synchronization.

Question: Based on the chapter's description of the mean solar day, which observation from Activity 11.3 would provide direct evidence that the mean solar day is 24 hours?
A. The shadow length is identical on two consecutive days at the same time of day
B. The time of the shortest shadow on successive days differs by approximately 24 hours
C. The shadow points in the same direction throughout each day
D. The length of the longest shadow equals the height of the stick
Show Answer & Explanation

Answer: (B) The time of the shortest shadow on successive days differs by approximately 24 hours

Explanation:
Activity 11.3 involves finding when the shadow is shortest (when the Sun is highest in the sky). If the shortest shadow occurs at approximately the same time each day, and students measure the time difference between these moments on consecutive days, that interval should be close to 24 hours, defining the mean solar day.

Question: Which statement best explains why many Indian festivals occur on different dates in the Gregorian calendar from year to year?
A. The Gregorian calendar intentionally shifts festival dates to balance religious observance
B. The festivals are tied to lunar phases or luni-solar calendar months, which do not correspond to fixed Gregorian calendar dates
C. Earth's orbital speed varies, causing the calendar to adjust automatically
D. Festival dates are calculated differently in each region of India
Show Answer & Explanation

Answer: (B) The festivals are tied to lunar phases or luni-solar calendar months, which do not correspond to fixed Gregorian calendar dates

Explanation:
The chapter explicitly states that festivals based on lunar or luni-solar calendars shift because these calendar systems follow Moon phases rather than fixed solar calendar dates. The luni-solar calendar's intercalary month keeps seasonal alignment but not Gregorian alignment, causing festivals to fall on different Gregorian dates.

Question: According to the chapter's discussion of artificial satellites, most satellites orbiting Earth at approximately 800 km altitude complete one orbit in roughly 100 minutes. What does this tell us about the Moon's orbit compared to satellite orbits?
A. The Moon orbits much faster than satellites because it is closer to Earth
B. The Moon takes much longer to complete its orbit because it is much farther from Earth
C. The Moon and satellites have identical orbital periods despite different altitudes
D. The Moon's orbital speed is decreasing while satellite speeds remain constant
Show Answer & Explanation

Answer: (B) The Moon takes much longer to complete its orbit because it is much farther from Earth

Explanation:
Satellites at 800 km altitude take about 100 minutes to orbit, while the Moon, much farther away, takes about 29.5 days to orbit Earth. This demonstrates that objects farther from Earth have longer orbital periods, consistent with gravitational principles discussed implicitly through the chapter's astronomical observations.

Question: How do the waxing and waning periods of the Moon, as described in the chapter, differ in terms of when they are most easily visible from Earth?
A. Both periods are equally visible at all times of night
B. The waxing period is easiest to see at sunset; the waning period at sunrise
C. The waning period is easiest to see at sunset; the waxing period at sunrise
D. Neither period is particularly easy to observe due to the Moon's position near the Sun
Show Answer & Explanation

Answer: (B) The waxing period is easiest to see at sunset; the waning period at sunrise

Explanation:
The chapter states plainly: 'A waxing Moon is easiest to spot at sunset, and a waning Moon at sunrise.' This is because during waxing the Moon is on the opposite side of Earth from where it is during waning, affecting which time of day it is visible and how far it has moved from the Sun.

Question: The Taittirīya Saṁhitā, mentioned in the chapter's 'Our scientific heritage' section, records observations that the Sun appears to move northward for six months and southward for six months. What are these apparent movements called?
A. Precession and nutation of Earth's axis
B. Uttarayan and Dakshinayan
C. Aphelion and perihelion shifts
D. Lunar nodes and Moon's ecliptic
Show Answer & Explanation

Answer: (B) Uttarayan and Dakshinayan

Explanation:
The chapter explicitly names these observed patterns: Uttarayan is the Sun's apparent northward movement from December to June, and Dakshinayan is its apparent southward movement from June to December. These ancient Indian observations directly correspond to the solstices and the seasons, demonstrating sophisticated early astronomical knowledge.

Question: Which of the following best describes why eclipses do not occur during every full Moon and every new Moon despite the chapter's explanation that lunar eclipses require full Moon and solar eclipses require new Moon?
A. Earth's shadow is too small to reach the Moon at these distances
B. The Moon's orbit is slightly tilted relative to Earth's orbit around the Sun, so alignment sufficient for an eclipse occurs only at certain orbital positions
C. The Moon's distance from Earth varies so greatly that sometimes it passes above or below Earth's shadow
D. Eclipses are rare events that happen roughly once every few years regardless of Moon phase
Show Answer & Explanation

Answer: (B) The Moon's orbit is slightly tilted relative to Earth's orbit around the Sun, so alignment sufficient for an eclipse occurs only at certain orbital positions

Explanation:
The chapter's 'A step further' box on lunar and solar eclipses explains clearly that the Moon's slightly tilted orbit means eclipses can only happen when the Moon reaches specific 'positions favourable for eclipses.' At most full and new Moon days, the alignment is not favorable, so no eclipse occurs even though the phase would otherwise allow it.

Question: Considering the relationship between the sidereal year and tropical year mentioned in the chapter, which consequence would result if the Indian National Calendar were based on the sidereal year instead of the tropical year?
A. Festivals would occur on the same Gregorian dates every year
B. The calendar would lose synchronization with seasonal cycles because the sidereal year is slightly longer
C. The calendar would remain synchronized with seasons because both years measure the same phenomenon
D. Leap years would need to be added every 3 years instead of every 4
Show Answer & Explanation

Answer: (B) The calendar would lose synchronization with seasonal cycles because the sidereal year is slightly longer

Explanation:
The chapter explains that the tropical year (365.2422 days) measures the time between spring equinoxes and aligns with seasons, while the sidereal year is about 20 minutes longer. Using the sidereal year would cause the calendar to drift backward relative to seasons over centuries, eventually placing spring equinox in winter months.

Question: When Meera observed the Moon during daylight at the Patang Mahotsav, she noticed it did not appear as a full circle. Based on the chapter's explanation of Moon phases, what does this observation reveal about the relative positions of the Sun, Moon, and Earth at that moment?
A. The Moon was between the Earth and Sun, so only a small portion of its illuminated side faced Earth
B. The Moon was directly opposite the Sun, making most of its illuminated portion visible
C. The Moon had moved farther from Earth, making it appear smaller and less bright
D. Clouds were blocking part of the Moon's surface from view during daytime
Show Answer & Explanation

Answer: (A) The Moon was between the Earth and Sun, so only a small portion of its illuminated side faced Earth

Explanation:
At any given time in the lunar cycle, Earth observes only the illuminated portion of the Moon that happens to face toward us. When the Moon appears as a crescent or thin phase during the day, it indicates the Moon is positioned closer to the Sun in the sky—meaning only a small sliver of the sun-facing side is oriented toward Earth. This is consistent with Activity 11.1's finding that the Moon moves closer to the Sun as its bright portion decreases.

Question: In Activity 11.2, when a student holds the ball opposite the lamp direction while their head (representing Earth) faces the lamp, what does the illuminated portion of the ball resemble?
A. A thin crescent, similar to the crescent Moon phase
B. A full bright circle, matching the full Moon phase
C. A half-circle, corresponding to the quarter Moon
D. A gibbous shape, showing more than half illumination
Show Answer & Explanation

Answer: (B) A full bright circle, matching the full Moon phase

Explanation:
Position A in Activity 11.2 places the ball opposite to the lamp's direction. From the observer's viewpoint (the head), the entire sunlit hemisphere of the ball becomes visible, producing a full, completely illuminated circle—exactly matching the appearance of the full Moon when it is positioned opposite the Sun in Earth's orbit.

Question: According to the chapter, the waning period of the Moon is referred to as Krishna Paksha in India. During which portion of the lunar month does this period occur?
A. From new Moon through the first week toward full Moon
B. From full Moon as the bright portion decreases back toward new Moon
C. Only during the first crescent phase after new Moon
D. Throughout the entire month regardless of the Moon's position
Show Answer & Explanation

Answer: (B) From full Moon as the bright portion decreases back toward new Moon

Explanation:
The chapter explicitly defines the waning period as the time when the bright portion of the Moon decreases—beginning after the full Moon and continuing until the new Moon day. This two-week interval, when less and less of the illuminated portion is visible, is called the Krishna Paksha or waning period in India.

Question: Based on the chapter's discussion of locating the Moon, if you observe the Moon at the same time each morning and it appears progressively closer to the Sun over several days, which phase of the lunar cycle are you witnessing?
A. The waxing phase, when the Moon's bright portion grows
B. The waning phase, when the Moon's bright portion shrinks
C. The transition from new Moon to full Moon
D. A lunar eclipse occurring during the cycle
Show Answer & Explanation

Answer: (B) The waning phase, when the Moon's bright portion shrinks

Explanation:
The chapter states that during the waning phase, as the Moon's bright part continues to decrease, the Moon appears to move closer in the sky to the Sun. If observations at the same time each day show the Moon drifting progressively nearer the Sun's direction, this indicates the waning phase when the illuminated portion is shrinking.

Question: The chapter explains that a lunar calendar year contains 12 lunar months, totaling approximately 354 days. What problem does this create for agricultural societies that depend on seasonal planting?
A. The lunar year is longer than the solar year, causing crops to grow too long
B. The lunar year is shorter than the solar year of 365 days, causing seasons to drift backward through the months each year
C. The lunar months are too short for crops to mature properly
D. Lunar months have inconsistent lengths, making planting schedules unpredictable
Show Answer & Explanation

Answer: (B) The lunar year is shorter than the solar year of 365 days, causing seasons to drift backward through the months each year

Explanation:
• The lunar year spans about 354 days while seasons repeat every ~365 days
• This 11-day shortfall accumulates, so seasons gradually shift to earlier lunar months year after year
• After several years, planting seasons end up in the wrong months relative to actual seasonal conditions
• This mismatch is why luni-solar calendars add intercalary months to realign the lunar and solar cycles.

Question: According to the chapter's explanation of the Gregorian calendar's leap year system, why is a leap day added every four years?
A. To account for the extra quarter day that accumulates each year as Earth revolves around the Sun
B. To ensure that February always has the same number of days as other months
C. To match the Indian National Calendar's structure
D. To correct for the gradual slowing of Earth's rotation
Show Answer & Explanation

Answer: (A) To account for the extra quarter day that accumulates each year as Earth revolves around the Sun

Explanation:
The chapter states that Earth takes nearly 365 and a quarter days to complete one revolution around the Sun. These extra quarter days accumulate to approximately one full day every four years, which the Gregorian calendar accommodates by adding a leap day every four years.

Question: The chapter mentions that at certain times during a lunar month, the Moon rises in the eastern sky during afternoon hours around 2:00–4:00 p.m., even though the Sun is still visible. What does this observation demonstrate about the Moon's position relative to the Sun?
A. The Moon is always closer to Earth during these hours
B. The Moon and Sun can occupy different parts of the sky simultaneously because the Moon is much closer to Earth than the Sun
C. The Moon is in its waxing phase and has moved ahead of the Sun in its orbit
D. The Moon's orbit causes it to pass in front of the Sun every few weeks
Show Answer & Explanation

Answer: (B) The Moon and Sun can occupy different parts of the sky simultaneously because the Moon is much closer to Earth than the Sun

Explanation:
Because the Moon orbits Earth at a much closer distance than the Sun, the two bodies can appear in different directions from Earth even when the Sun illuminates our daytime sky. Afternoon moonrise visibility shows the Moon has shifted its position independent of the Sun's apparent location, highlighting the geometric separation between their positions.

Question: Based on the chapter's description of luni-solar calendars and the intercalary month system, approximately how often must an extra month be added, and what triggers this timing?
A. Every year, because the lunar and solar cycles differ by exactly one month annually
B. Every 2 to 3 years, when the accumulated difference between 12 lunar months and the solar year grows close to a full month
C. Every 7 years, matching the seven-phase cycle of the Moon
D. Only when a lunar eclipse occurs, as indicated by celestial alignment
Show Answer & Explanation

Answer: (B) Every 2 to 3 years, when the accumulated difference between 12 lunar months and the solar year grows close to a full month

Explanation:
The chapter states that twelve lunar months sum to 354 days, falling short of the 365-day solar year by about 11 days. Over 2 to 3 years, these deficits accumulate to nearly a full month's worth of difference, at which point an intercalary month (Adhika Maasa) is inserted to synchronize the calendar with seasons.

Question: The chapter notes that the mean solar day—the time for the Sun to return to its highest point in the sky—is based on which periodic phenomenon?
A. The Moon's revolution around Earth
B. The rotation of Earth around its own axis
C. Earth's revolution around the Sun
D. The precession of Earth's axis over centuries
Show Answer & Explanation

Answer: (B) The rotation of Earth around its own axis

Explanation:
The chapter explicitly defines the mean solar day as originating from Earth's rotation around its own axis. This rotation causes the Sun to appear to rise in the east and set in the west each day, creating the natural cycle of day and night that forms the foundation for the 24-hour day measurement.

Question: In Activity 11.1, observers documented that the Moon became invisible for several days partway through the observation period. According to the chapter, on which day of the lunar cycle does this occur, and what astronomical condition creates this invisibility?
A. On the full Moon day, when the entire illuminated side faces away from Earth
B. On the new Moon day, when only the non-illuminated side of the Moon faces Earth
C. During the waxing crescent phase, when moonlight is too faint to see at night
D. During solar eclipses, when Earth's shadow blocks all sunlight from the Moon
Show Answer & Explanation

Answer: (B) On the new Moon day, when only the non-illuminated side of the Moon faces Earth

Explanation:
The chapter identifies the new Moon day (Amavasya) as the time when the Moon is not visible from Earth. At this point in the lunar cycle, the Moon is positioned between the Earth and Sun, so only the non-illuminated hemisphere faces our planet, rendering the Moon invisible against the bright daytime sky.

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