Question 1. The apparent southward movement of the Sun from June to December is called:
A. Uttarayan
B. Dakshinayan
C. Shukla Paksha
D. Krishna Paksha
Answer: B. Dakshinayan
Question 2. Approximately how long does it take to complete one lunar cycle from one full moon to the next?
A. 30.5 days
B. 29.5 days
C. 365 days
D. 14 days
Answer: B. 29.5 days
Question 3. On which day is the Moon generally not visible from Earth?
A. Full moon day
B. Crescent moon day
C. New moon day
D. Half-moon day
Answer: C. New moon day
Question 4. When the visible illuminated portion of the Moon gradually increases, the Moon is said to be in the:
A. Waning phase
B. Waxing phase
C. Eclipse phase
D. Dark phase
Answer: B. Waxing phase
Question 5. As the Moon changes from a full moon towards a new moon, its illuminated portion:
A. Increases continuously
B. Remains unchanged
C. Decreases gradually
D. Becomes completely invisible immediately
Answer: C. Decreases gradually
Question 6. Which part of the Moon remains without sunlight at any given time?
A. The half facing away from the Sun
B. The half facing Earth
C. The upper half
D. The lower half
Answer: A. The half facing away from the Sun
Question 7. The natural event used as the basis for defining one day is primarily related to:
A. Earth's rotation
B. Earth's revolution around the Sun
C. The Moon's revolution around Earth
D. The changing seasons
Answer: A. Earth's rotation
Question 8. A mean solar day represents the time interval between:
A. Two consecutive moonrises
B. Two consecutive sunrises
C. The Sun reaching its highest position on two successive days
D. Two consecutive full moons
Answer: C. The Sun reaching its highest position on two successive days
Question 9. The cycle associated with the definition of a solar year is mainly connected with:
A. The rotation of the Moon
B. The revolution of Earth around the Sun
C. Earth's rotation about its axis
D. The phases of Venus
Answer: B. The revolution of Earth around the Sun
Question 10. The different shapes of the illuminated part of the Moon observed from Earth are known as:
A. Lunar positions
B. Moon cycles
C. Phases of the Moon
D. Solar patterns
Answer: C. Phases of the Moon
Question 11. The Earth takes approximately how much time to complete one revolution around the Sun?
A. 354 days
B. 365 days exactly
C. 365 days and about 6 hours
D. 29.5 days
Answer: C. 365 days and about 6 hours
Question 12. Calendars that mainly use the Moon's cycle for counting months are called:
A. Solar calendars
B. Seasonal calendars
C. Gregorian calendars
D. Lunar calendars
Answer: D. Lunar calendars
Question 13. Twelve lunar months together have a duration of approximately:
A. 354 days
B. 365 days
C. 400 days
D. 180 days
Answer: A. 354 days
Question 14. Which calendar is based on the tropical year?
A. Lunar calendar
B. Gregorian calendar
C. Seasonal calendar
D. Cartosat calendar
Answer: B. Gregorian calendar
Question 15. A calendar that uses lunar phases while also making adjustments to remain aligned with the seasons is known as a:
A. Solar calendar
B. Lunar calendar
C. Lunisolar calendar
D. Tropical calendar
Answer: C. Lunisolar calendar
Question 16. In the Indian context, the period during which the Moon's bright portion decreases is called:
A. Shukla Paksha
B. Uttarayan
C. Dakshinayan
D. Krishna Paksha
Answer: D. Krishna Paksha
Question 17. A lunar eclipse can occur only on a:
A. New moon day
B. Crescent moon day
C. Full moon day
D. Quarter moon day
Answer: C. Full moon day
Question 1. Why does the Moon appear bright even though it does not produce its own light?
Answer: The Moon appears bright because it reflects sunlight.
Question 2. What is meant by the phases of the Moon?
Answer: The different shapes of the illuminated portion of the Moon visible from Earth are called the phases of the Moon.
Question 3. Why does the visible shape of the Moon change during a month?
Answer: As the Moon revolves around Earth, its position relative to Earth and the Sun changes. Therefore, different portions of its illuminated half become visible from Earth.
Question 4. Approximately how long does the Moon take to complete one lunar cycle?
Answer: Approximately 29.5 days.
Question 5. What is a new moon?
Answer: It is the phase when the Moon is not visible from Earth because its illuminated side faces away from us.
Question 6. What is a full moon?
Answer: It is the phase in which the entire visible face of the Moon appears illuminated.
Question 7. How much time approximately passes between a new moon and a full moon?
Answer: About two weeks.
Question 8. What does the term waxing Moon mean?
Answer: It refers to the phase during which the illuminated portion of the Moon visible from Earth gradually increases.
Question 9. What does the term waning Moon mean?
Answer: It refers to the phase during which the visible illuminated portion of the Moon gradually decreases.
Question 10. During which phase does the Moon's bright portion increase?
Answer: During the waxing phase.
Question 11. During which phase does the visible bright portion of the Moon decrease?
Answer: During the waning phase.
Question 12. Name the main phases through which the Moon passes from the new moon to the full moon.
Answer: The Moon passes through waxing crescent, first quarter, waxing gibbous and finally reaches the full moon.
Question 13. What phases occur as the Moon moves from a full moon towards a new moon?
Answer: The Moon passes through waning gibbous, last quarter, waning crescent and then reaches the new moon.
Question 14. At what time is a waning Moon generally easier to observe?
Answer: Around sunrise.
Question 15. What is the approximate duration of Earth's rotation about its axis?
Answer: About 24 hours.
Question 16. What natural motion forms the basis for measuring one day?
Answer: Earth's rotation about its own axis.
Question 17. What natural phenomenon was used to establish the idea of a month?
Answer: The repeating cycle of the phases of the Moon was used as the basis for a month.
Question 18. What natural cycle helped humans define a year?
Answer: The repeating cycle of seasons, associated with Earth's revolution around the Sun, helped define a year.
Question 19. Approximately how long does Earth take to complete one revolution around the Sun?
Answer: About 365 days and nearly 6 hours. More precisely, the extra time is approximately 5 hours and 48 minutes.
Question 20. Why is the length of a year not exactly 365 days?
Answer: Earth takes approximately 365 days plus about 5 hours and 48 minutes to complete one revolution around the Sun.
Question 21. What is a lunar calendar?
Answer: A lunar calendar is a calendar in which months are mainly based on the cycle of the Moon.
Question 22. How many days are approximately present in twelve lunar months?
Answer: Approximately 354 days.
Question 23. What is a tropical year?
Answer: A tropical year is the time interval between two successive spring equinoxes.
Question 24. Which widely used calendar is based on the tropical year?
Answer: The Gregorian calendar.
Question 25. What is a lunisolar calendar?
Answer: It is a calendar that follows the phases of the Moon but also makes adjustments to remain synchronised with the seasonal or solar cycle.
Question 26. What is meant by the apparent northward movement of the Sun?
Answer: The apparent northward movement of the Sun is called Uttarayan.
Question 27. What is the apparent southward movement of the Sun known as?
Answer: It is called Dakshinayan.
Question 28. During which part of the year does the apparent southward movement of the Sun occur?
Answer: From approximately June to December.
Question 29. On which lunar phase is the Moon closest to the Sun in its apparent position in the sky?
Answer: On the new moon day.
Question 30. During which phase is the Moon apparently farthest from the Sun in the sky?
Answer: During the full moon phase.
Question 31. When does the Moon rise on a full moon day?
Answer: The Moon rises approximately at sunset.
Question 32. When does the Moon set on a full moon day?
Answer: The Moon sets approximately around sunrise.
Question 33. Why can the same Moon generally be observed from different places on Earth during the same night?
Answer: Earth's rotation takes about 24 hours, whereas the Moon's orbital position changes slowly over approximately 29.5 days. Therefore, the Moon's position changes only gradually during a single day.
Question 34. What is the approximate relationship between Earth's rotational period and the Moon's orbital period?
Answer: Earth rotates once in about 24 hours, whereas the Moon takes approximately 29.5 days to complete its lunar cycle.
Question 35. What are artificial satellites?
Answer: Artificial satellites are human-made objects placed in orbit for specific scientific, technological or practical purposes.
Question 36. Mention four uses of artificial satellites.
Answer: Artificial satellites are used for communication, navigation, weather monitoring and mapping. GPS is also an important application.
Question 37. How are satellites useful in communication?
Answer: They help transmit television, telephone, internet and other communication signals over large distances.
Question 38. How do satellites assist in navigation?
Answer: Satellites provide location and positioning information used by navigation systems such as GPS.
Question 39. How are satellites used in weather monitoring?
Answer: They observe clouds, atmospheric conditions and weather systems, helping in weather forecasting and monitoring.
Question 40. How do satellites help in mapping?
Answer: Satellite observations can be used to collect information about Earth's surface and prepare maps.
Question 41. How are satellites useful for studying objects in space?
Answer: They can observe stars and other celestial bodies and contribute to astronomical research.
Question 42. Why are natural cycles important in the measurement of time?
Answer: Natural repeating events such as Earth's rotation, the phases of the Moon and Earth's revolution around the Sun provide the basis for defining units such as a day, month and year.
Question 43.
Riya observes the Moon for several nights. She notices that the illuminated part visible from Earth becomes larger each night.
(a) Which phase of the Moon is Riya observing: waxing or waning?
(b) Explain why the visible illuminated portion is increasing, even though the Moon does not change its shape.
Answer:
(a) Riya is observing the waxing phase.
(b) The Moon is always illuminated by the Sun on one side. As it revolves around Earth, its position relative to Earth and the Sun changes. Therefore, we see an increasing portion of its illuminated half.
Question 44
A student claims:
> “The Moon is fully illuminated on a full moon night because the entire Moon receives sunlight.”
Is the student's statement correct? Give a reason. Also state approximately when the Moon rises and sets on a full moon day.
Answer:
The statement is not completely correct. At any time, only one half of the Moon receives sunlight. During a full moon, the illuminated half is facing Earth, so it appears fully bright to us.
On a full moon day:
The Moon rises approximately at sunset.
The Moon sets approximately at sunrise.
Question 45.
Suppose a civilisation decides to make its calendar using only the phases of the Moon. Each month is taken as approximately 29.5 days.
(a) Approximately how many days will be present in 12 such months?
(b) Why might such a calendar gradually fail to remain aligned with the seasons?
Answer:
(a)
$$
12 \times 29.5 = 354 \text{ days}
$$
Therefore, 12 lunar months contain approximately 354 days.
(b) A solar year is approximately 365 days and nearly 6 hours, whereas 12 lunar months give only about 354 days. Thus, there is a difference of about 11 days each year. Over time, the calendar would gradually shift relative to the seasons.
Question 46.
A student says:
> “Since Earth completes one rotation in about 24 hours and the Moon takes about 29.5 days to complete its lunar cycle, the Moon's position changes much more slowly than the Earth's rotation.”
Using this information, explain why people at different locations on Earth can generally observe a similar lunar phase on the same day.
Answer:
Earth rotates rapidly, completing one rotation in about 24 hours, whereas the Moon's position changes gradually over approximately 29.5 days.
Therefore, during a single day, the Moon does not move through a large part of its lunar cycle. As a result, observers at different locations on Earth generally see the same phase of the Moon, although the exact time of moonrise and moonset may differ.
Question 47.
Three communities use different methods to organise their calendars:
Community A uses only the phases of the Moon.
Community B uses the cycle of seasons and the tropical year.
Community C uses lunar months but makes adjustments so that its calendar remains connected with the seasons.
Identify the type of calendar used by each community.
Answer:
| Community | Type of Calendar |
| Community A | Lunar calendar |
| Community B | Solar calendar based on the tropical year |
| Community C | Lunisolar calendar |
The Gregorian calendar is based on the tropical year, which is the time interval between two successive spring equinoxes.