Question 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.
(ii) The shadow of Earth blocks sunlight from reaching the Moon causing phases.
(iii) Calendars are based on various astronomical cycles which repeat in a predictable manner.
(iv) The Moon can only be seen at night.

Accepted Answer

(i) True: We see the Moon because sunlight reflects off its surface towards us.
(ii) False: The phases of the Moon are caused by the changing positions of the Moon relative to the Earth and Sun, not Earth's shadow. Earth's shadow causes lunar eclipses.
(iii) True: Calendars are based on predictable astronomical cycles like the Earth's rotation and revolution, and the Moon's phases.
(iv) False: The Moon can be seen during the day as well as at night, depending on its position in the sky. — The Moon shines by reflected sunlight, so only the illuminated part facing Earth is visible. Earth's shadow causes eclipses, not phases. Calendars rely on predictable cycles of celestial bodies. The Moon is visible in the day or night depending on its orbit.

Question 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.

Accepted Answer

No, Amol's birthday does not fall on the full Moon day every year because the Moon's phases follow a lunar cycle of about 29.5 days, which does not match exactly with the solar calendar year of 365 days. Therefore, the full Moon date shifts each year with respect to the solar calendar. — The lunar month is shorter than the solar month, so the full Moon occurs about 11 days earlier each year in the solar calendar. Hence, the full Moon date changes every year.

Question 3

Name two things that are incorrect in Fig. 11.10.

Accepted Answer

Two incorrect things in Fig. 11.10 are:
1. The direction of sunlight might be wrongly shown.
2. The positions or labels of the Moon phases may be incorrect.
(Note: The exact errors depend on the figure details, but common mistakes include incorrect illumination or phase representation.) — Fig. 11.10 likely shows Moon phases or Earth-Moon-Sun positions. Errors often involve wrong sunlight direction or incorrect phase labeling, which can misrepresent how phases occur.

Question 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.

Picture label (e.g. A, B, C, etc.) - Phase of Moon
- Three days after New Moon
- Full Moon
- Three days after Full Moon
- A week after Full Moon
- Day of New Moon

(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.

Accepted Answer

(i) The correct panel numbers corresponding to the phases are:
- Three days after New Moon: Panel showing waxing crescent (e.g., B)
- Full Moon: Panel showing fully illuminated Moon (e.g., D)
- Three days after Full Moon: Panel showing waning gibbous (e.g., E)
- A week after Full Moon: Panel showing waning crescent (e.g., F)
- Day of New Moon: Panel showing no visible Moon (e.g., A)

(Note: Exact panel letters depend on figure labeling.)

(ii) The phases never seen from Earth are the far side of the Moon, which is never visible due to synchronous rotation. Therefore, any picture showing the far side or phases not illuminated towards Earth are never seen. — Moon phases progress from New Moon (no visible illumination) to waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, last quarter, waning crescent, and back to New Moon. The far side is never visible from Earth.

Question 5

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?

Accepted Answer

(i) The phase of the Moon overhead at sunset is the full Moon phase. The Moon is fully illuminated and opposite the Sun in the sky.
(ii) The Moon is neither waxing nor waning at full Moon; it is at the peak of illumination. After full Moon, it starts waning. — At sunset, the full Moon rises opposite the Sun and appears overhead around midnight. The full Moon is fully illuminated, marking the transition from waxing to waning phases.

Question 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?

Accepted Answer

Ravi is telling the truth. A crescent Moon rises shortly after the Sun sets, so it can be seen rising in the East at sunset.
Kaushalya's observation is also possible because a gibbous Moon can be visible in the afternoon sky in the East before it sets.
Therefore, both can be telling the truth depending on the Moon's phase and time of observation. — The crescent Moon appears shortly after sunset, rising in the East. The gibbous Moon can be seen in the afternoon sky before it sets in the West. Both observations are consistent with Moon phases and positions.

Question 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?

Accepted Answer

Luni-solar calendars will need an intercalary month more often because as the Moon moves farther away and its revolution slows, the lunar month lengthens slightly. This causes the lunar year to drift more relative to the solar year, requiring more frequent intercalary months to realign the calendar. — The increasing distance and slower revolution of the Moon lengthen the lunar cycle, increasing the difference between lunar and solar years, thus increasing the need for intercalary months.

Question 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.

Accepted Answer

There are 36 months in 3 years (12 months × 3 years = 36 months). Since there are 37 full Moons in these 3 years, by the pigeonhole principle, at least one month must have 2 full Moons.
Hence, at least two full Moons occur in the same month. — With 37 full Moons and only 36 months, placing each full Moon in a month means one month must contain at least two full Moons.

Question 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?

Accepted Answer

Vaishali would have seen the full Moon phase because the full Moon rises at sunset and sets at sunrise, making it visible throughout the night. — The full Moon is opposite the Sun, so it is visible all night from sunset to sunrise.

Question 10

If we stopped having leap years, in approximately how many years would the Indian Independence day happen in winter?

Accepted Answer

If leap years were stopped, the calendar would lose about 1 day every 4 years relative to the solar year. Over about 100 years, this would accumulate to about 25 days, shifting dates significantly. Indian Independence Day (15 August) would gradually shift into winter after approximately 100 to 120 years. — Without leap years, the calendar drifts by about 1 day every 4 years. After about a century, this drift causes seasonal dates to shift by about a month, moving Independence Day into winter.

Question 11

What is the purpose of launching artificial satellites?

Accepted Answer

Artificial satellites are launched for various purposes including communication, weather forecasting, navigation (GPS), scientific research, Earth observation, and space exploration. — Satellites help in transmitting signals, monitoring weather, mapping Earth, studying space, and enabling global positioning systems.

Question 12

On which periodic phenomenon are the following measures of time based: (i) day (ii) month (iii) year?

Accepted Answer

(i) Day: Based on the Earth's rotation on its axis.
(ii) Month: Based on the Moon's revolution around the Earth (lunar cycle).
(iii) Year: Based on the Earth's revolution around the Sun. — A day is the time Earth takes to rotate once, a month is the time the Moon takes to orbit Earth, and a year is the time Earth takes to orbit the Sun.

Question 13

Which celestial body's apparent motion primarily forms the basis of a day on Earth?

Accepted Answer

Sun — The apparent motion of the Sun across the sky from east to west causes the cycle of day and night, thus forming the basis of a day on Earth.

Question 14

What causes the day and night cycle on Earth?

Accepted Answer

Earth's rotation on its axis — Day and night occur because Earth spins around its axis once approximately every 24 hours, causing different parts of Earth to face the Sun or face away from it.

Question 15

The Earth rotates from which direction to which direction?

Accepted Answer

West to East — Earth rotates from west to east, which causes the Sun to appear to rise in the east and set in the west.

Keeping Time with the Skies

Keeping Time with the Skies — Study Notes

Introduction

Day and Night

The Moon and Its Phases

Practice Questions — Keeping Time with the Skies

All 13 Chapters in Curiosity