Phases of the Moon are caused by:

Relative positions of Sun, Earth, Moon

The reason Moonrise time shifts daily is:

Earth rotates and Moon moves in orbit

A day (mean solar day) is based on:

Earth’s rotation – Sun’s highest position to next

Solar calendars keep months adding to:

365 days (plus leap adjustments)

Century correction in Gregorian calendar:

Only centuries divisible by 400 are leap years

Sidereal year is defined by:

Return of Sun to same star background

Why do many Indian festivals shift dates in Gregorian calendar?

They are tied to lunar/luni-solar dates

Eid-ul-Fitr is celebrated:

After sighting crescent at end of Ramazan

Festival dates can differ in East vs West India because:

Different time zones affect sunrise-based rules

Rashtriya Panchang is published by:

Positional Astronomy Center (IMD)

NCERT Solutions Class 8 Science - Curiosity Chapter 11 – Keeping Time with the Skies

Name: Keeping Time with the Skies – Class 8 Science - Curiosity
Uploaded: 2026-05-31
Description: The Moon appears to change shape because we see varying portions of its sunlit side as it orbits Earth. These phases form the basis of lunar months, calendars, and many festivals. Human-made satellites also orbit Earth, aiding communication, navigation, and scientific research.

Class 8 Science - Curiosity

Last Updated: 31 May 2026

Share on WhatsApp

Chapter Introduction

The Moon appears to change shape because we see varying portions of its sunlit side as it orbits Earth. These phases form the basis of lunar months, calendars, and many festivals. Human-made satellites also orbit Earth, aiding communication, navigation, and scientific research.

हिंदी में (Hindi)

चाँद का आकार बदलता दिखाई देता है क्योंकि हम उसके सूर्य-प्रकाशित हिस्से के अलग-अलग हिस्से पृथ्वी से देखते हैं। ये चंद्र चरण महीनों, कैलेंडरों और त्योहारों का आधार हैं। कृत्रिम उपग्रह भी पृथ्वी की परिक्रमा करते हैं, जो संचार, नेविगेशन और वैज्ञानिक अनुसंधान में मदद करते हैं।

Watch Video Lecture

Video Coming Soon..

Practice more on the App!

Get unlimited MCQ tests & video lectures.

Download

Important Points

🕐 Coming Soon

Important points for this chapter will be added shortly. Check back soon!

Practice MCQ Questions (59 questions)

Q1. Why does the Moon shine?

Q2. The changing shapes of the Moon seen from Earth are called:

Q3. Which day is the Moon not visible?

Q4. Time from one Full Moon to the next is about:

Q5. When the bright part of the Moon increases it is called:

Get all 59 MCQ questions + more!

Download the Genius Mind app for unlimited practice, mock tests & video lectures.

▶ Google Play

Frequently Asked Questions (FAQ)

🕐 Coming Soon

FAQs for this chapter will be added soon. Stay tuned!

Tough Words (Glossary)

spherical

Meaning: shaped like a ball

अर्थ: गोलाकार / गोले जैसा

"The Moon is spherical in shape."

reflect

Meaning: to bounce back light or sound

अर्थ: परावर्तित होना/करना

"The Moon looks bright because it reflects sunlight."

lunar eclipse

Meaning: when Earth's shadow falls on the Moon

अर्थ: चन्द्र ग्रहण

"A lunar eclipse can only happen on a full Moon day."

solar eclipse

Meaning: when the Moon blocks sunlight from reaching Earth

अर्थ: सूर्य ग्रहण

"A solar eclipse can happen only on a new Moon day."

phase

Meaning: the shape of the lit part of the Moon seen from Earth

अर्थ: चन्द्रमा का कला/चरण

"We see a different phase of the Moon every night."

waxing

Meaning: the lit part of the Moon is increasing

अर्थ: शुक्ल पक्ष (बढ़ती कला)

"During the waxing period, the Moon looks bigger each day."

waning

Meaning: the lit part of the Moon is decreasing

अर्थ: कृष्ण पक्ष (घटती कला)

"In the waning period, the Moon becomes thinner."

crescent

Meaning: a thin curved shape of the Moon

अर्थ: चन्द्रमा की पतली टेढ़ी आकृति (क्रेसेंट)

"We saw a thin crescent Moon after sunset."

gibbous

Meaning: more than half but not full

अर्थ: अधिवर्धित (अर्ध से अधिक, पूर्ण नहीं)

"A gibbous Moon lit up the evening sky."

illuminated

Meaning: lit up by light

अर्थ: प्रकाशित

"Only the illuminated half of the Moon is visible."

revolve

Meaning: to move around another object

अर्थ: परिक्रमा करना

"The Moon revolves around the Earth."

orbit

Meaning: the curved path of a moving object in space

अर्थ: कक्षा

"Satellites move in an orbit around Earth."

rotate

Meaning: to spin around an axis

अर्थ: घूर्णन करना

"Earth rotates once in about 24 hours."

axis

Meaning: an imaginary line around which something rotates

अर्थ: अक्ष

"Earth spins around its axis."

overhead

Meaning: directly above your head

अर्थ: सिर के ठीक ऊपर

"At sunrise the half Moon was almost overhead."

orientation

Meaning: the position or direction of something

अर्थ: अभिविन्यास / दिशा-स्थिति

"The phases change with the orientation of the Sun, Earth, and Moon."

apparent

Meaning: seeming to be, not necessarily true

अर्थ: प्रतीत / दिखाई देने वाला

"The Sun’s apparent motion is due to Earth’s rotation."

periodic

Meaning: happening regularly in a pattern

अर्थ: आवधिक

"Moon phases are periodic events."

cycle

Meaning: a series that repeats in the same order

अर्थ: चक्र

"One cycle of Moon phases takes about a month."

mean solar day

Meaning: average time from one noon to the next (≈24 h)

अर्थ: माध्य सौर दिवस (लगभग 24 घंटे)

"A mean solar day is taken as 24 hours."

equinox

Meaning: day when day and night are nearly equal

अर्थ: विषुव

"Spring equinox happens around March 21."

solstice

Meaning: day when the Sun is farthest north or south

अर्थ: अयनांत

"The summer solstice occurs around June 21."

Uttarayan

Meaning: the Sun’s apparent northward movement

अर्थ: उत्तरायण

"Makar Sankranti marks the start of Uttarayan."

Dakshinayan

Meaning: the Sun’s apparent southward movement

अर्थ: दक्षिणायन

"Dakshinayan lasts from June to December."

tropical year

Meaning: time from one spring equinox to the next

अर्थ: उष्णकटिबंधीय वर्ष

"The Gregorian calendar follows the tropical year."

sidereal year

Meaning: time taken for the stars to return to the same position

अर्थ: नाक्षत्र वर्ष

"The sidereal year is slightly longer than the tropical year."

synchronise

Meaning: to match the timing with something

अर्थ: समकालित करना / तालमेल बैठाना

"Leap years help synchronise the calendar with seasons."

leap year

Meaning: a year with an extra day to adjust the calendar

अर्थ: लीप वर्ष

"February has 29 days in a leap year."

intercalary

Meaning: an extra period inserted into a calendar

अर्थ: अधिमास / अतिरिक्त महीना

"Some calendars add an intercalary month to align with seasons."

Adhika Maasa

Meaning: the extra month added in luni-solar calendars

अर्थ: अधिक मास

"Adhika Maasa occurs every two to three years."

Amant

Meaning: calendar where a month starts after new Moon

अर्थ: अमान्त (अमावस्या के बाद शुरू होने वाला माह)

"In Amant calendars, the month begins after new Moon."

Purnimant

Meaning: calendar where a month starts after full Moon

अर्थ: पूर्णिमान्त (पूर्णिमा के बाद शुरू होने वाला माह)

"North India often uses the Purnimant system."

lunar calendar

Meaning: calendar based on Moon’s phases

अर्थ: चन्द्र आधारित पंचांग

"Islamic dates follow a lunar calendar."

solar calendar

Meaning: calendar based on the Sun’s motion

अर्थ: सौर पंचांग

"The Gregorian calendar is a solar calendar."

luni-solar calendar

Meaning: calendar using Moon months adjusted to the Sun year

अर्थ: चांद-सूर्य आधारित पंचांग (लूनी-सोलर)

"Many Indian festivals use a luni-solar calendar."

moonrise

Meaning: the time when the Moon appears above the horizon

अर्थ: चन्द्रोदय

"Moonrise is about 50 minutes later each day."

new Moon (Amavasya)

Meaning: day when the Moon is not visible

अर्थ: अमावस्या

"Eid can follow the sighting after the new Moon."

full Moon (Purnima)

Meaning: day when the Moon appears as a full circle

अर्थ: पूर्णिमा

"Buddha Purnima is celebrated on a full Moon."

timekeeping

Meaning: measuring and tracking time

अर्थ: समय-मान / समय गणना

"Phases of the Moon help in timekeeping."

obstruction

Meaning: something that blocks the view

अर्थ: अवरोध / रुकावट

"Choose a place without obstruction to watch the sky."

binoculars

Meaning: a device with two lenses to see distant objects

अर्थ: दूरबीन (दो लेंस वाली)

"We used binoculars to spot a satellite."

flickering

Meaning: shining with an unsteady light

अर्थ: टिमटिमाना / झिलमिलाना

"The satellite looked like a flickering point of light."

debris

Meaning: broken pieces left over from damage

अर्थ: मलबा / अवशेष

"Space agencies track dangerous space debris."

navigation

Meaning: finding and following a path

अर्थ: नेविगेशन / मार्ग-निर्देशन

"Satellites help in phone navigation."

terrain

Meaning: the natural features of land

अर्थ: भू-आकृति / स्थलाकृति

"Satellites map terrain for better planning."

constellation

Meaning: a pattern of stars in the sky

अर्थ: नक्षत्रमंडल / तारामंडल

"Capricorn is a constellation named in old texts."

wobble

Meaning: a slow, slight shaking or tilting movement

अर्थ: डगमगाना / डोलना

"Earth’s axis has a slow wobble over time."

satellite

Meaning: an object that orbits a planet

अर्थ: उपग्रह

"The Moon is Earth’s natural satellite."

celestial

Meaning: related to the sky or space

अर्थ: आकाशीय / खगोलीय

"Calendars use positions of celestial objects."

altitude

Meaning: height above Earth’s surface or sea level

अर्थ: ऊँचाई / उन्नति

"Many satellites orbit at an altitude of about 800 km."

NCERT Solutions Class 8 Science - Curiosity Chapter 11 – Keeping Time with the Skies

Chapter Introduction

Watch Video Lecture

Video Coming Soon..

Important Points

Practice MCQ Questions (59 questions)

Q1. Why does the Moon shine?

Q2. The changing shapes of the Moon seen from Earth are called:

Q3. Which day is the Moon not visible?

Q4. Time from one Full Moon to the next is about:

Q5. When the bright part of the Moon increases it is called:

Q6. In India, waxing phase is called:

Q7. In India, waning phase is called:

Q8. A crescent Moon shows:

Q9. A gibbous Moon shows:

Q10. On Full Moon day, the Moon is nearly:

Q11. On New Moon day, the Moon appears:

Q12. The Moon rises each day approximately:

Q13. A waning Moon is easiest to spot around:

Q14. A waxing Moon is easiest to spot around:

Q15. Phases of the Moon are caused by:

Q16. Lunar eclipses can occur only on:

Q17. Solar eclipses can occur only on:

Q18. The line dividing bright and dark parts on Moon’s disk is:

Q19. At sunrise after Full Moon, the Moon appears roughly:

Q20. As days pass after Full Moon, at sunrise the Moon appears:

Q21. Half Moon (Last Quarter) at sunrise is roughly:

Q22. The reason Moonrise time shifts daily is:

Q23. During New Moon the illuminated half of Moon faces:

Q24. A day (mean solar day) is based on:

Q25. Average duration of a mean solar day is:

Q26. The period from one Full Moon to next defines:

Q27. Number of lunar months in about one year of seasons:

Q28. Length of a lunar year (~12 lunar months) is about:

Q29. Solar calendars keep months adding to:

Q30. Leap year rule in Gregorian calendar (basic):

Q31. Century correction in Gregorian calendar:

Q32. Tropical year is measured between:

Q33. Sidereal year is defined by:

Q34. Indian National Calendar (Saka) begins its year on:

Q35. Indian National Calendar is primarily:

Q36. In Indian National Calendar, leap day is added to:

Q37. Luni-solar calendars keep seasons in sync by:

Q38. Adhika Maasa refers to:

Q39. Amant calendars start month:

Q40. Purnimant calendars start month:

Q41. Uttarayan refers to:

Q42. Why do many Indian festivals shift dates in Gregorian calendar?

Q43. Diwali occurs on:

Q44. Holi occurs on:

Q45. Eid-ul-Fitr is celebrated:

Q46. Makar Sankranti follows a:

Q47. Because sidereal and tropical years differ slightly, Makar Sankranti shifts by one day roughly every:

Q48. Festival dates can differ in East vs West India because:

Q49. Rashtriya Panchang is published by:

Q50. The Moon is Earth’s:

Q51. Typical low Earth orbit satellites circle Earth in roughly:

Q52. Artificial satellites help in:

Q53. ISRO’s Cartosat series is used for:

Q54. AstroSat is India’s:

Q55. Chandrayaan missions target the:

Q56. Aditya-L1 studies the:

Q57. Space debris refers to:

Q58. Father of the Indian Space Programme:

Q59. Students’ small satellites launched with ISRO include: