Complete Solutions and Summary of Keeping Time with the Skies – Curiosity Class 8 Science Chapter 11 – Summary, Questions, Answers, Extra Questions
Detailed summary, explanations, question answers, and extra solved questions for Curiosity Class VIII Science Chapter 11 ‘Keeping Time with the Skies’
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Keeping Time with the Skies
Chapter 11: Astronomy and Time Measurement
Complete Study Guide with Interactive Learning
Chapter Overview
What You'll Learn
Moon's Phases
Understanding how and why the Moon's appearance changes over a month.
Calendars Evolution
Exploring lunar, solar, and luni-solar calendars and their basis.
Festivals & Astronomy
Linking Indian festivals to astronomical events like Moon phases.
Artificial Satellites
Role of satellites in communication, navigation, and science.
Historical Context
This chapter explores how ancient observations of the Moon, Sun, and seasons led to calendars. In India, texts like Taittirīya Saṁhitā and Surya Siddhanta noted solar movements. The Indian National Calendar, based on Saka Era, starts on March 22, syncing with equinoxes. ISRO's satellites like Cartosat and AstroSat continue this heritage of sky observation.
Key Highlights
The Moon's phases cycle every 29.5 days, defining months. Solar year is 365.25 days, with leap years adjusting calendars. Festivals like Diwali tie to lunar phases. Artificial satellites orbit at 800 km, aiding weather and research.
Comprehensive Chapter Summary
1. Introduction to Moon's Appearance
The chapter begins with Meera observing the Moon during daytime at Patang Mahotsav. It questions why the Moon's shape changes, not due to eclipses but its position relative to Sun and Earth. Definition: Phases of the Moon are changing shapes of its bright portion as seen from Earth.
2. Observing Moon's Changes
Activity 11.1
Document Moon at sunrise/sunset, shading bright portion, noting size changes and Sun separation. Waning: Bright portion decreases from full to new Moon. Waxing: Increases from new to full. Cycle: ~29.5 days.
Definition: Waning period (Krishna Paksha) - bright part shrinks; Waxing period (Shukla Paksha) - bright part grows.
Phases Explained
Full Moon (Purnima): Entire illuminated portion visible. New Moon (Amavasya): Illuminated portion not visible. Gibbous: More than half illuminated. Crescent: Less than half.
More details: Moon revolves around Earth; half facing Sun illuminated, but view from Earth varies.
Locating the Moon
Moon position shifts; waning Moon at sunrise, waxing at sunset. Moonrise delays ~50 minutes daily due to orbital motion.
Definition: Moonrise - time Moon appears above horizon, varies daily.
3. Understanding Observations
Activity 11.2
Use ball (Moon), torch (Sun), head (Earth) to simulate phases. Illuminated portion changes with position; curved boundary separates lit/dark parts.
Phases Mechanism
Moon doesn't change shape; view of illuminated half varies. On full Moon, entire lit side faces Earth; new Moon, dark side faces Earth.
More: Earth’s shadow causes eclipses, not phases. Eclipses rare due to Moon’s orbital tilt.
Moon's Delay
Moon advances in orbit during Earth's rotation, so appears 50 minutes later daily.
4. Calendars Evolution
Solar Day
Activity 11.3: Measure shortest shadow for Sun's highest point. Mean solar day: 24 hours.
Definition: Mean solar day - average time for Sun to return to highest position.
5. Lunar and Solar Calendars
Lunar Calendars
Based on Moon phases; 12 months ~354 days. Seasons shift as not synced with solar year.
More: Amant/Purnimant variants; months like Chaitra, Vaisakha.
Solar Calendars
Based on seasons; 365 days + leap year every 4 years (Gregorian). Adjusts for 365.25-day tropical year.
Definition: Tropical year - time between spring equinoxes; Sidereal year - star-based, 20 min longer.
6. Luni-Solar and Indian Calendars
Luni-solar: Lunar months with extra (Adhika Maasa) every 2-3 years to sync seasons. Indian National Calendar: Solar, starts March 22, 365 days.
More: Surya Siddhanta principles; CRC in 1952 unified calendars.
7. Festivals and Astronomy
Many tied to Moon: Diwali (new Moon Kartika), Holi (full Moon Phalguna). Solar: Makar Sankranti ~same Gregorian date, shifts due to precession.
Definition: Precession - Earth's axis wobble, shifts festival dates over centuries.
8. Artificial Satellites
Man-made, orbit ~800 km, ~100 min per orbit. ISRO: Cartosat (mapping), AstroSat (astronomy). Activity 11.4: Spot moving points in sky.
More: Space debris issue; Vikram Sarabhai pioneered Indian space program.
9. Additional Notes
Tides linked to Moon; rise/fall ~50 min delay like Moonrise.
Key Concepts and Definitions
Phases of the Moon
Changing shapes of Moon's bright portion from Earth, due to relative positions of Sun, Moon, Earth.
Waxing/Waning
Waxing: Bright part increases (Shukla Paksha). Waning: Decreases (Krishna Paksha).
Mean Solar Day
Average 24 hours for Sun to return to highest sky position.
Lunar Month
~29.5 days for Moon's phase cycle.
Solar Year
~365.25 days for Earth's revolution around Sun.
Leap Year
Extra day every 4 years to sync calendar with seasons.
Luni-Solar Calendar
Lunar-based with extra month (Adhika Maasa) to align with solar year.
Indian National Calendar
Solar calendar starting March 22, with 30/31-day months.
Artificial Satellite
Man-made object orbiting Earth for communication, navigation, etc.
Important Facts and Figures
Questions and Answers from Chapter
Short Questions
Q1. State whether the following statements are True or False. (i) We can only see that part of the Moon which reflects sunlight towards us.
Q2. State whether the following statements are True or False. (ii) The shadow of Earth blocks sunlight from reaching the Moon causing phases.
Q3. State whether the following statements are True or False. (iii) Calendars are based on various astronomical cycles which repeat in a predictable manner.
Q4. State whether the following statements are True or False. (iv) The Moon can only be seen at night.
Q5. 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?
Q6. What is the purpose of launching artificial satellites?
Q7. On which periodic phenomenon are the following measures of time based: (i) day
Q8. On which periodic phenomenon are the following measures of time based: (ii) month
Q9. On which periodic phenomenon are the following measures of time based: (iii) year?
Q10. Name two things that are incorrect in Fig. 11.10.
Q11. If we didn’t have clocks or calendars, how else could we measure time?
Q12. Have you ever seen the Moon during the day?
Q13. What would happen if Earth had two moons instead of one?
Q14. Imagine you lived on the Moon instead of Earth. What would you mean by a day, a month or a year?
Q15. On a particular night, Vaishali saw the Moon in the sky from sunset to sunrise. What phase of the Moon would she have noticed?
Medium Questions
Q1. 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.
Q2. 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?
Q3. 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?
Q4. 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.
Q5. If we stopped having leap years, in approximately how many years would the Indian Independence day happen in winter?
Q6. Look at the pictures of the Moon in Fig. 11.11, and answer the following questions. (i) Write the correct panel number corresponding to the phases of the Moon shown in the pictures above.
Q7. Name two things that are incorrect in Fig. 11.10.
Q8. 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?
Q9. On a particular night, Vaishali saw the Moon in the sky from sunset to sunrise. What phase of the Moon would she have noticed?
Q10. What would happen if Earth had two moons instead of one? How would that change the night sky?
Q11. If we didn’t have clocks or calendars, how else could we measure time?
Q12. Have you ever seen the Moon during the day? Why do you think it is sometimes visible when the Sun is up?
Q13. Imagine you lived on the Moon instead of Earth. What would you mean by a day, a month or a year?
Q14. 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?
Q15. 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?
Long Questions
Q1. 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.
Q2. Name two things that are incorrect in Fig. 11.10.
Q3. Look at the pictures of the Moon in Fig. 11.11, 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.
Q4. 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?
Q5. 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?
Q6. 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?
Q7. 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.
Q8. On a particular night, Vaishali saw the Moon in the sky from sunset to sunrise. What phase of the Moon would she have noticed?
Q9. If we stopped having leap years, in approximately how many years would the Indian Independence day happen in winter?
Q10. What is the purpose of launching artificial satellites?
Q11. On which periodic phenomenon are the following measures of time based: (i) day (ii) month (iii) year?
Q12. The Moon’s crescent always faces towards the Sun (Fig. 11.12). On days when you see the crescent Moon, point your finger towards the Sun, and slowly move it across the sky towards the Moon taking as short a path as you can. Note how your finger always crosses the illuminated part of the Moon first and clearly shows us that we see sunlight reflected off the Moon.
Q13. Most of the dates in the Indian National Calendar always map to the same dates in the Gregorian calendar. Can you find out which ones may differ for certain years?
Q14. Different states in India celebrate the New Year according to their local cultures. Find out the names of the New Year festival celebrated in any 10 states of India. Also find out whether it is based on the lunar calendar or the solar calendar or the luni-solar calendar.
Q15. Collect Gregorian calendars for the last five years... try to guess which year might have included an intercalary month (Adhikamaasa).
Interactive Knowledge Quiz
Test your understanding of Keeping Time with the Skies
Quick Revision Notes
Moon Phases
- Waxing: Increases
- Waning: Decreases
- Cycle: 29.5 days
Calendars
- Lunar: 354 days
- Solar: 365 days
- Luni-solar: Extra month
Festivals
- Diwali: New Moon
- Holi: Full Moon
- Sankranti: Solar
Satellites
- Orbit: 800km
- Time: 100 min
- ISRO: Cartosat
Exam Strategy Tips
- Draw phases diagrams
- Explain activities
- Compare calendars
- Use figures
- Link to heritage
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