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Important Questions Chapter 11 Class 8 Science Curiosity CBSE Board

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Keeping Time with the Skies


Short Questions

1. Why can we see the Moon during the day?
Answer: The Moon reflects sunlight and can be visible when it’s above the horizon during daylight.

2.What causes the Moon’s phases?
Answer: The changing angle of sunlight on the Moon as it orbits Earth.

3.What is a full Moon day called in India?
Answer: Purnima.

4.What is a new Moon day called in India?
Answer: Amavasya.

5.What is the waning period of the Moon?
Answer: When the Moon’s bright portion decreases.

6.What is the waxing period of the Moon?
Answer: When the Moon’s bright portion increases.

7.How long is a lunar month?
Answer: About 29.5 days.

8.What is a solar day?
Answer: The time the Sun takes to reach its highest point in the sky, about 24 hours.

9.Why do lunar calendars have 354 days in a year?
Answer: Because 12 lunar months of 29.5 days add up to 354 days.

10.What is a leap year?
Answer: A year with an extra day added to keep the calendar in sync with seasons.

11.What is the Indian National Calendar based on?
Answer: The solar year, starting after the spring equinox.

12.What is Uttarayana?
Anwer: The Sun’s apparent northward movement from December to June.

13.What is Dakshinayana?
Answer: The Sun’s apparent southward movement from June to December.

14.Why are artificial satellites launched?
Answer: For communication, navigation, weather monitoring, and research.

15.What is the name of ISRO’s satellite for mapping?
Answer: Cartosat.


Long Questions

1. Why does the Moon appear to change shape every night?
Answer: The Moon’s shape changes due to the angle of sunlight it reflects as it orbits Earth. These changes are called phases, seen differently each day from Earth.

2.How does the Moon’s position in the sky change over a month?
Answer: The Moon moves closer to or farther from the Sun in the sky daily. It rises about 50 minutes later each day due to its orbit around Earth.

3.Why don’t lunar eclipses happen every full Moon?
Answer: Lunar eclipses only occur when the Moon passes through Earth’s shadow, which requires a specific alignment. The Moon’s orbit is slightly tilted, so this alignment is rare.

4.How do solar calendars differ from lunar calendars?
Answer: Solar calendars are based on Earth’s revolution around the Sun (365 days), syncing with seasons. Lunar calendars follow the Moon’s phases (354 days), causing seasons to shift.

5.What is a luni-solar calendar, and how does it work?
Answer: A luni-solar calendar uses the Moon’s phases for months but adds an extra month every few years. This keeps it aligned with the solar year and seasons.

6.Why do Indian festivals like Diwali fall on different Gregorian dates each year?
Answer: Many Indian festivals follow lunar or luni-solar calendars, which don’t align with the Gregorian solar calendar. This causes dates to shift annually, sometimes by about 11 days.

7.How does the Indian National Calendar differ from the Gregorian calendar?
Answer: The Indian National Calendar is a solar calendar starting on March 22, with fixed month lengths. The Gregorian calendar has varied month lengths and starts on January 1.

8.What role did Meghnad Saha play in calendar reform?
Answer: Meghnad Saha chaired the Calendar Reform Committee, which created the Indian National Calendar. It was adopted in 1956 to unify timekeeping in India.

9.How do tides relate to the Moon’s position?
Answer: Tides rise and fall due to the Moon’s gravitational pull, following its position. High or low tides occur about 50 minutes later each day, matching the Moon’s movement.

10.Why do festivals like Makar Sankranti shift slightly in the Gregorian calendar?
Answer: Makar Sankranti follows the solar sidereal calendar, which differs slightly from the tropical year. This causes a gradual shift of about one day every 11 years.

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