11.7 Summary & Keep the Curiosity Alive
Key Points
- The Moon shines by reflecting sunlight. As it revolves around the Earth, we see different amounts of its sunlit half — giving the phases (new → crescent → gibbous → full and back), a cycle of about a month. The phases are not caused by the Earth’s shadow.
- Full Moon = Purnima, new Moon = Amavasya; waxing (Shukla Paksha) shows best at sunset, waning (Krishna Paksha) at sunrise. The Moon rises ~50 minutes later each day.
- Three sky cycles give three units: the day (Earth’s rotation, ~24 h), the month (Moon’s phases, ~29.5 days), and the year (Earth’s revolution, ~365¼ days).
- Lunar calendars follow the Moon (354-day year, so seasons drift); solar calendars follow the seasons (365 days, with a leap day every 4 years); luni-solar calendars combine both, adding an Adhika Maasa every few years. The Indian National Calendar is a solar calendar of the Shaka Era.
- Many festivals follow the Moon, so their Gregorian dates shift each year.
- The Moon is Earth’s natural satellite; artificial satellites (launched by ISRO and others) aid communication, navigation, weather and research.
A Closing Challenge: Keep the Curiosity Alive
Think It Through
- Moon by day. Explain how it’s possible to see the Moon in the afternoon sky.
- Bust the myth. A classmate insists the Moon’s phases are the Earth’s shadow. How would you correct them — and what does the Earth’s shadow cause?
- Two moons? Imagine Earth had two moons. How might that change the night sky and our idea of a “month”?
- Spot a satellite. Just after sunset, look for a steady point of light moving fast across the sky (use a satellite-tracker app). How is its motion different from a star’s or a plane’s?
- Leap-year hunt. Which of these are leap years: 2024, 2025, 1900, 2000? (Use the century-÷400 rule.)
We’ve read time in the sky. Next, we come back to Earth to see how every living thing is woven together — the web of life in Chapter 12.