CBSE Class 8 Science Chapter 11: Keeping Time with the Skies — Assertion & Reason
CBSE Class 8 Science Assertion & Reason
Expert crafted · Instant PDF download · 2026-27
The following Assertion and Reason questions are based on Chapter 11: Keeping Time with the Skies from the NCERT Class 8 Science textbook Curiosity. Each question has four options — read both the Assertion (A) and Reason (R) carefully before selecting your answer.
How to attempt Assertion & Reason questions:
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is NOT the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is NOT the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Assertion & Reason Questions
1
Assertion (A): The Moon appears different on different days.
Reason (R): We can only see the illuminated portion of the Moon that faces the Earth.
Reason (R): We can only see the illuminated portion of the Moon that faces the Earth.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. As the Moon revolves around Earth, different parts of its illuminated half face us, causing the changing appearance we call phases.
2
Assertion (A): The phases of the Moon are caused by Earth's shadow falling on the Moon.
Reason (R): The Moon revolves around the Earth in about a month.
Reason (R): The Moon revolves around the Earth in about a month.
Answer: (c)
A is false, but R is true. Moon phases are NOT caused by Earth's shadow (that would be a lunar eclipse). Phases occur because we see different portions of the Moon's illuminated half as it revolves around Earth.
3
Assertion (A): On a full Moon day, the Moon is nearly opposite the Sun in the sky.
Reason (R): When the Sun rises in the East on a full Moon day, the Moon is almost setting in the West.
Reason (R): When the Sun rises in the East on a full Moon day, the Moon is almost setting in the West.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The full Moon occurs when the entire illuminated half faces Earth, which happens when the Moon is on the opposite side of Earth from the Sun.
4
Assertion (A): The Moon takes about 29.5 days to cycle through all its phases.
Reason (R): The cycle of Moon's phases forms the basis for a month in calendars.
Reason (R): The cycle of Moon's phases forms the basis for a month in calendars.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The regular 29.5-day cycle from one new Moon to the next provides a natural time period that was used to define the month.
5
Assertion (A): During the waning period, the bright portion of the Moon decreases.
Reason (R): The waning period is also called Krishna Paksha in India.
Reason (R): The waning period is also called Krishna Paksha in India.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. While both statements are true, the name Krishna Paksha is just what this period is called in India—it doesn't explain why the bright portion decreases.
6
Assertion (A): The Moon rises about 50 minutes later each day.
Reason (R): The Moon moves ahead in its orbit while Earth completes one rotation in 24 hours.
Reason (R): The Moon moves ahead in its orbit while Earth completes one rotation in 24 hours.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. As the Moon progresses in its orbit around Earth, Earth needs to rotate a bit more than 24 hours for the Moon to appear in nearly the same spot in the sky.
7
Assertion (A): A waxing Moon is easiest to spot at sunset.
Reason (R): During the waxing phase, the Moon appears closer to the Sun in the sky.
Reason (R): During the waxing phase, the Moon appears closer to the Sun in the sky.
Answer: (c)
A is true, but R is false. A waxing Moon is easiest to spot at sunset, but during waxing the Moon actually appears FARTHER from the Sun in the sky compared to the new Moon position.
8
Assertion (A): The mean solar day is 24 hours.
Reason (R): This is the average time the Sun takes to go from its highest position in the sky on one day to the highest position the next day.
Reason (R): This is the average time the Sun takes to go from its highest position in the sky on one day to the highest position the next day.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The rotation of Earth around its axis causes this regular cycle of the Sun's apparent motion, which defines the mean solar day of 24 hours.
9
Assertion (A): A lunar year consists of 12 lunar months totaling 354 days.
Reason (R): The seasons remain synchronized to the same lunar months every year in a lunar calendar.
Reason (R): The seasons remain synchronized to the same lunar months every year in a lunar calendar.
Answer: (c)
A is true, but R is false. While a lunar year is 354 days, seasons do NOT remain synchronized because the solar year (365 days) and lunar year differ by 11 days.
10
Assertion (A): The Gregorian calendar adds a leap day every four years.
Reason (R): Earth takes approximately 365 and a quarter days to complete one revolution around the Sun.
Reason (R): Earth takes approximately 365 and a quarter days to complete one revolution around the Sun.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The extra quarter day accumulates to approximately one full day every four years, so leap years add an extra day to keep the calendar synchronized with seasons.
11
Assertion (A): Luni-solar calendars add an intercalary month every few years.
Reason (R): This keeps both the lunar cycle and the solar year synchronized.
Reason (R): This keeps both the lunar cycle and the solar year synchronized.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The 11-day difference between the lunar year (354 days) and solar year (365 days) accumulates to nearly a full month every 2-3 years, requiring an extra month.
12
Assertion (A): The Indian National Calendar is a solar calendar.
Reason (R): It begins on 22 March, the day after the spring equinox.
Reason (R): It begins on 22 March, the day after the spring equinox.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Starting the year on the day after the spring equinox directly links the calendar to the Earth's position in its orbit around the Sun.
13
Assertion (A): Most Indian festivals fall on different dates in the Gregorian calendar each year.
Reason (R): These festivals are based on lunar or luni-solar calendars rather than the solar Gregorian calendar.
Reason (R): These festivals are based on lunar or luni-solar calendars rather than the solar Gregorian calendar.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Festivals like Diwali and Holi follow Moon phases in luni-solar calendars, so their Gregorian dates shift each year.
14
Assertion (A): Makar Sankranti occurs on almost the same date every year in the Gregorian calendar.
Reason (R): Makar Sankranti follows a solar sidereal calendar.
Reason (R): Makar Sankranti follows a solar sidereal calendar.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Solar sidereal calendar-based festivals remain tied to Earth's position relative to distant stars, resulting in nearly the same Gregorian date annually.
15
Assertion (A): Artificial satellites help us in communication, navigation, and weather monitoring.
Reason (R): Most artificial satellites orbit about 800 km above Earth's surface and take roughly 100 minutes to complete one orbit.
Reason (R): Most artificial satellites orbit about 800 km above Earth's surface and take roughly 100 minutes to complete one orbit.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. While satellites do serve these purposes and have these orbital characteristics, the orbital height and period don't explain their usefulness—that comes from the technology they carry.
❓ Frequently Asked Questions
What is covered in CBSE Class 8 Science Chapter 11 Keeping Time with the Skies?
This chapter covers all key topics from Keeping Time with the Skies as per CBSE 2026-27 syllabus.
Is this Assertion & Reason useful for CBSE board exams?
Yes, designed for CBSE Class 8 board exam preparation covering the complete syllabus.
Are these CBSE Class 8 Science Assertion & Reason updated for 2026-27?
Yes, all content at eBookPublisher is updated as per the latest 2026-27 CBSE syllabus.
How many chapters are in CBSE Class 8 Science?
All chapters of CBSE Class 8 Science are covered at eBookPublisher with free Assertion & Reason for each chapter.
Can I study Keeping Time with the Skies online for free?
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