Keeping Time with the Skies
Keep the curiosity alive
1. State whether the following statements are True or False.
(i) We can only see that part of the Moon which reflects sunlight towards us.
True
(ii) The shadow of Earth blocks sunlight from reaching the Moon causing phases.
False
(iii) Calendars are based on various astronomical cycles which repeat in a predictable manner.
True
(iv) The Moon can only be seen at night.
False
2. 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
Answer:- No, Amol’s birthday will not fall on a full Moon day every year. The lunar calendar, based on the Moon’s phases, has a year of about 354 days, while the Gregorian calendar, used for birthdays, has about 365 days. This 11-day difference causes the full Moon to occur on different dates each year in the Gregorian calendar. So, May 6 will not always align with a full Moon day.
3. Name two things that are incorrect in Fig. 11.10.
Answer:-
In Fig. 11.10, two things that are incorrect are:
1. The Moon is shown with stars behind it, which is not possible as the Moon is much closer to Earth than the stars.
2. The Moon appears to be partially covered by clouds, but clouds do not affect the Moon’s phases; the phases are caused by the changing angles of sunlight reflecting off the Moon.
4. 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. 
Answer:-
| Phase of Moon | Picture label |
|---|---|
| Three days after New Moon | A |
| Full Moon | E |
| Three days after Full Moon | F |
| A week after Full Moon | D |
| Day of New Moon | B |
(ii) List the picture labels of the phases of the Moon that are never seen from Earth. Hint: You can use your observations from Activity 11.1 or Fig. 11.2 as reference.
Answer:- B
5. Malini saw the Moon overhead in the sky at sunset.
(i) Draw the phase of the Moon that Malini saw.
Answer:-
(ii) Is the Moon in the waxing or the waning phase?
Answer:-The Moon is in the waxing phase.
6. 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?
Answer:-Ravi is telling the truth.
7. 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?
Answer :- As the Moon gets farther from Earth and its revolution slows, it takes longer to complete its orbit around Earth. This means the lunar month (about 29.5 days now) will become slightly longer. In a luni-solar calendar, 12 lunar months (about 354 days) are shorter than a solar year (365 days), so an intercalary month (Adhika Maasa) is added every 2-3 years to sync with the solar year. If lunar months get longer, the lunar year will be closer to the solar year, reducing the gap (currently about 11 days). This means the accumulated difference will take longer to reach a full month, so luni-solar calendars will need an intercalary month less often.
8. 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.
Answer :- In 3 years, a solar calendar has 36 months (3 × 12). With 37 full Moons, there are more full Moons than months. Therefore, at least one month must have two full Moons.
9. On a particular night, Vaishali saw the Moon in the sky from sunset to sunrise. What phase of the Moon would she have noticed?
Answer :- If the Moon is visible from sunset to sunrise, it rises as the Sun sets and sets as the Sun rises, which happens on a full Moon.
10. If we stopped having leap years, in approximately how many years would the Indian Independence day happen in winter?
Answer :- Without leap years, the calendar would drift backward by about 0.25 days per year because the Earth takes approximately 365.25 days to orbit the Sun, but a non-leap year calendar would only count 365 days. Indian Independence Day is on August 15, which is in summer in the Northern Hemisphere. Winter in India is typically around December to February, so shifting August 15 to, say, January (mid-winter) requires a drift of about 5 months, or roughly 150 days (5 months × 30 days). At a drift of 0.25 days per year, it would take approximately 150 ÷ 0.25 = 600 years for Indian Independence Day to occur in winter.
11. What is the purpose of launching artificial satellites?
Answer:- Artificial satellites are launched to help with communication, navigation, weather monitoring, disaster management, and scientific research. For example, they can improve maps, plan cities, monitor natural disasters, and study stars and other celestial objects.
12. On which periodic phenomenon are the following measures of time based: (i) day (ii) month (iii) year?
Answer:-
(i) Day: Based on the Earth’s rotation on its axis, which makes the Sun appear to rise and set every 24 hours.
(ii) Month: Based on the Moon’s phase cycle, which takes about 29.5 days to complete.
(iii) Year: Based on the Earth’s revolution around the Sun, which takes about 365.25 days to complete one cycle of seasons.
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