DAV Class 6 SST Chapter 4 Question Answer The Motions of the Earth (Day-Night and Seasons)

Looking for the most authentic, 100% textbook-grounded DAV Class 6 Social Science Chapter 4 Solutions: The Motions of the Earth (Day-Night and Seasons)? Based strictly on the prescribed DAV CMC textbook We and Our World, this comprehensive master guide provides complete answers for Section A (Tick the correct option with scientific justifications), Section B (Fill in the blanks), Section C (Match the following table), Section D (Short Answer Questions), Section E (Detailed Long Answer Questions with full structural points), Value-Based Questions (VBQ), HOTS (Higher Order Thinking Skills), astronomical comparison tables (Rotation vs Revolution, Solstices vs Equinoxes), and authentic DAV Board Examination Previous Years’ Questions (2018-2024) with official marking schemes.

Section A: Tick (✓) the Correct Option

1. On 22nd December, the sun rays are vertical at the:
(a) Tropic of Cancer
(b) Tropic of Capricorn
(c) Equator
(d) Arctic Circle
Answer: (b) Tropic of Capricorn
Detailed Justification: On 22nd December (Winter Solstice), the Southern Hemisphere is tilted towards the Sun. The midday sun shines vertically overhead at the Tropic of Capricorn (23½° S latitude). Consequently, the Southern Hemisphere experiences summer with longer days and shorter nights, while the Northern Hemisphere experiences winter.

2. Which statement about a leap year is incorrect?
(a) It has 366 days.
(b) February has 29 days.
(c) It occurs once in four years.
(d) February has 28 days.
Answer: (d) February has 28 days.
Detailed Justification: In a normal year, February has 28 days and the year has 365 days. However, in a leap year, the accumulated 6 surplus hours from each of the four preceding years (6 × 4 = 24 hours = 1 full day) are added to February, making it a 29-day month with a total of 366 days in the year. Therefore, statement (d) is incorrect for a leap year.

3. If there is noon on one side of the earth, the opposite side will have:
(a) Morning
(b) Evening
(c) Midnight
(d) Dawn
Answer: (c) Midnight
Detailed Justification: The Earth is a spherical body that rotates on its axis from west to east. Because the Sun illuminates only half of the Earth at any given time, the half facing directly towards the Sun experiences midday (noon), while the diametrically opposite half (180° away) is completely turned away from sunlight, experiencing midnight.

4. On 23rd September, mid-day sun is overhead at the:
(a) Tropic of Cancer
(b) Tropic of Capricorn
(c) Equator
(d) South Pole
Answer: (c) Equator
Detailed Justification: On 23rd September (Autumnal Equinox), neither pole of the Earth is tilted towards or away from the Sun. The rays of the midday sun fall vertically directly over the Equator (0° latitude). On this day, all places across the entire Earth experience equal duration of day and night (12 hours of day and 12 hours of night).

5. The angle of sun rays on 21st June on the Tropic of Cancer is:
(a) 66½°
(b) 45°
(c) 90°
(d) 23½°
Answer: (c) 90°
Detailed Justification: On 21st June (Summer Solstice), the Northern Hemisphere is inclined towards the Sun. The Sun reaches its highest point in the sky and shines vertically perpendicular (at an angle of 90°) over the Tropic of Cancer (23½° N latitude).

Section B: Fill in the Blanks

1. The earth revolves around the sun in a fixed path called as orbit (an elliptical orbit).
2. The angle of inclination of the earth’s axis is 66½° with its orbital plane (and 23½° with the perpendicular to the orbital plane).
3. Two motions of the earth are rotation and revolution.
4. The time period immediately before sunrise is called dawn (while the period immediately following sunset is called dusk or twilight).
5. The earth completes one revolution around the sun in 365 days and 6 hours (approximately 365 days, 5 hours, 48 minutes, and 46 seconds).

Section C: Match the Following

Column A (Textbook Term / Phenomenon)	Column B (Correct Match)	Scientific Explanation
1. The duration of day and night is equal in both hemispheres on	(e) 23rd September and 21st March	These two dates are known as the Equinoxes, when direct sun rays fall vertically over the Equator.
2. The Arctic Circle has six-month long days in	(c) Summer Solstice	When the North Pole remains continuously tilted towards the Sun from March 21 to September 23, the region beyond the Arctic Circle has continuous daylight for 6 months.
3. The Tropic of Capricorn is located in	(a) Southern Hemisphere	The Tropic of Capricorn is the special parallel of latitude located at 23½° South of the Equator.
4. The rays of the sun are vertical on Tropic of Cancer and Tropic of Capricorn	(b) On 21st June and 22nd December respectively	21st June marks the Summer Solstice in the north (Tropic of Cancer), while 22nd December marks the Winter Solstice (Tropic of Capricorn).
5. Spring equinox is also called	(d) Vernal equinox	The equinox occurring on 21st March marks the beginning of spring in the Northern Hemisphere and is termed the Vernal Equinox.

Section D: Answer the Following Questions in Brief

Question 1: What is rotation? How much time does the Earth take in completing one rotation?
Answer:
The spinning motion of the Earth on its imaginary tilted axis from west to east is called rotation.
Key Features & Duration:

• Duration: The Earth takes approximately 24 hours (strictly 23 hours, 56 minutes, and 4.09 seconds) to complete one single rotation. This duration is known as an Earth Day or solar day.
• Direction: From west to east, which is why celestial bodies including the Sun appear to rise in the east and set in the west.
• Primary Effect: Rotation causes the alternation of day and night and the daily rising and falling of tides.

Question 2: What is meant by the revolution of the Earth?
Answer:
The movement of the Earth around the Sun in a fixed elliptical orbit at a uniform speed is called the revolution of the Earth.
Key Characteristics:

• Path: An oval-shaped, elliptical path known as Earth’s orbit.
• Time Period: It takes 365 days and 6 hours (365¼ days) to complete one full revolution around the Sun.
• Average Orbital Speed: Approximately 29.8 km per second (approx. 1,07,000 km/hr).
• Primary Consequence: Earth’s revolution, combined with the inclined axis, causes the change of seasons and varying lengths of day and night throughout the year.

Question 3: What is a leap year?
Answer:
A year having 366 days instead of the normal 365 days, with the extra day added to the month of February (making it 29 days instead of 28 days), is called a Leap Year.
Why it Occurs:

• The Earth takes 365 days and 6 hours to complete one revolution around the Sun.
• For ordinary calendar convenience, we count only 365 days in a standard year and ignore the surplus 6 hours.
• Over 4 successive years, these surplus 6 hours accumulate: 6 hours × 4 = 24 hours = 1 whole day.
• This additional 1 day is added to February every fourth year. Leap years are always evenly divisible by 4 (e.g., 2020, 2024, 2028).

Question 4: What is an equinox? Which seasons are indicated by it in both the hemispheres?
Answer:
An equinox (derived from Latin meaning “equal night”) is the celestial position when the midday Sun shines vertically overhead at the Equator, resulting in equal lengths of day and night (12 hours day and 12 hours night) all across the globe.
Equinoxes occur twice every year:

1. 21st March (Spring / Vernal Equinox):
   • Northern Hemisphere: Experiences Spring season.
   • Southern Hemisphere: Experiences Autumn season.
2. 23rd September (Autumnal Equinox):
   • Northern Hemisphere: Experiences Autumn season.
   • Southern Hemisphere: Experiences Spring season.

Question 5: Why does the duration of day and night change in a year?
Answer:
The duration of day and night changes throughout the year due to two combined factors:

1. The Inclination of Earth’s Axis: The Earth’s axis is not perpendicular to its orbital plane; it is tilted at a constant angle of 66½° to its orbital plane (or 23½° to the vertical).
2. Earth’s Revolution: As the Earth orbits the Sun while maintaining this fixed axial tilt in the same direction (parallelism of the axis), different hemispheres lean towards the Sun at different times of the year:
   • When a hemisphere is tilted towards the Sun, it receives longer periods of sunlight, resulting in longer days and shorter nights (summer).
   • When that hemisphere is tilted away from the Sun, it receives less daylight, resulting in shorter days and longer nights (winter).

Note: If the Earth’s axis were completely vertical, day and night would be exactly 12 hours long everywhere on Earth all year round.

Section E: Answer the Following Questions in Detail

Question 1: Why are days and nights equal on 21st March at all places on the Earth? Explain.
Answer:
Days and nights are of equal length (12 hours of day and 12 hours of night) all over the Earth on 21st March because of the following scientific reasons:

1. Vertical Rays on Equator: On 21st March, the Earth reaches a position in its orbit where neither the North Pole nor the South Pole is tilted towards or away from the Sun. The midday Sun shines directly overhead at an angle of 90° over the Equator (0° latitude).
2. Circle of Illumination Bisects All Parallels: The Circle of Illumination (the boundary dividing daylight from darkness) passes precisely through both the North Pole and the South Pole. Consequently, it divides every parallel of latitude across the entire planet into two exactly equal halves of 180° each.
3. Equal Insolation: Both the Northern and Southern Hemispheres receive an equal amount of solar insolation and heat.
4. Vernal Equinox Phenomenon: Because every point on the revolving Earth spends exactly half of its 24-hour rotation cycle in sunlight and half in darkness, the duration of day and night is exactly equal (12 hours each) worldwide. This date marks the Vernal (Spring) Equinox in the Northern Hemisphere.

Question 2: Explain why seasons are reversed between the Northern and Southern Hemispheres.
Answer:
Seasons are reversed between the Northern and Southern Hemispheres because the Earth’s axis is inclined at an angle of 66½° to its orbital plane and always points in the same direction in space (towards Polaris, the North Star) as the Earth revolves around the Sun.

This creates opposite seasonal conditions across four key planetary positions:

1. Position on 21st June (Summer Solstice in the North):
   • The Northern Hemisphere is tilted towards the Sun. The Sun’s rays fall vertically on the Tropic of Cancer (23½° N).
   • The Northern Hemisphere experiences Summer with long days and short nights. The Arctic region enjoys 24 hours of continuous daylight.
   • At the same time, the Southern Hemisphere is tilted away from the Sun, receiving slanting rays. It experiences Winter with short days, long nights, and cold temperatures.
2. Position on 23rd September (Autumnal Equinox):
   • Sun rays fall vertically over the Equator. Both hemispheres receive equal heat.
   • The Northern Hemisphere transitions into Autumn, whereas the Southern Hemisphere transitions into Spring.
3. Position on 22nd December (Winter Solstice in the North):
   • The Southern Hemisphere is tilted directly towards the Sun, receiving vertical rays on the Tropic of Capricorn (23½° S).
   • The Southern Hemisphere experiences Summer (e.g., Christmas in Australia is celebrated in warm summer weather).
   • The Northern Hemisphere is tilted away from the Sun, receiving slanting rays, experiencing Winter with short days and freezing nights.
4. Position on 21st March (Vernal Equinox):
   • Sun rays once again fall directly on the Equator.
   • The Northern Hemisphere enters Spring, while the Southern Hemisphere enters Autumn.

Conclusion: When one hemisphere leans towards the Sun, the other naturally leans away, causing the seasons to always be completely reversed between the two halves of our globe.

Question 3: Why does the month of February have 29 days after every four years? Explain.
Answer:
The occurrence of 29 days in February every four years is a direct astronomical adjustment to align our human calendar year with the actual physical orbital period of the Earth around the Sun.

Mathematical & Astronomical Derivation:

1. Actual Revolution Period: The Earth takes precisely 365 days, 5 hours, 48 minutes, and 46 seconds (roughly 365 days and 6 hours or 365¼ days) to complete one revolution around the Sun. This is called a Solar Year.
2. The Standard Calendar Problem: For everyday convenience, a standard civil calendar year counts only 365 days. This leaves an uncounted surplus of approximately 6 hours every single year.
3. Four-Year Accumulation: Over four consecutive years, these neglected 6 hours accumulate:
   6 hours × 4 years = 24 hours = 1 complete solar day (24 hours)
4. Addition to February: If this accumulated day were ignored, our calendar seasons would gradually shift forward by approximately 24 days every century. To prevent this drift, this 1 full extra day is added to the shortest month of the year, February, every fourth year.
5. Result: In that fourth year, February has 29 days instead of 28, and the entire year comprises 366 days. This year is termed a Leap Year.

Question 4: How do day and night occur on the Earth? Explain with the help of a descriptive diagrammatic breakdown.
Answer:
The occurrence of day and night is caused by the spherical shape of the Earth combined with its continuous rotation on its axis.

Step-by-Step Breakdown:

1. Spherical Shape of the Earth: Because the Earth is a spherical, opaque body, sunlight cannot pass through it or illuminate all sides at once. The Sun can illuminate only one half of the Earth’s surface at any single moment.
2. The Circle of Illumination: The imaginary circular boundary line that separates the lighted daylight half of the Earth from the dark night half is called the Circle of Illumination.
3. West-to-East Rotation: The Earth constantly rotates on its tilted axis from west to east, completing one rotation in roughly 24 hours:
   • The half of the Earth that is turned towards the Sun receives light and experiences Day.
   • The opposite half that is turned away from the Sun remains in shadow and experiences Night.
4. Gradual Transitions (Dawn and Dusk): As the Earth steadily rotates, different longitudes continuously cross the Circle of Illumination:
   • Dawn: The period of diffused light immediately before the Sun appears above the eastern horizon.
   • Dusk (Twilight): The period of faint lingering light immediately after the Sun sinks below the western horizon.

Key Takeaway: If the Earth did not rotate, the side facing the Sun would experience perpetual, boiling daylight, while the other side would remain in freezing, eternal darkness, making human and biological life entirely impossible.

Core Scientific Comparison Tables

1. Difference Between Rotation and Revolution

Feature / Parameter	Rotation of the Earth	Revolution of the Earth
Basic Definition	Spinning of the Earth on its own imaginary axis.	Movement of the Earth around the Sun in a fixed elliptical path.
Path / Line of Motion	Internal axis tilted at 66½° to its orbital plane.	External elliptical orbit around the Sun.
Time Taken	Takes approximately 24 hours (1 solar day).	Takes 365 days and 6 hours (1 solar year).
Direction	West to East (counter-clockwise from above North Pole).	Counter-clockwise along its elliptical orbit.
Primary Effect	Causes the alternation of day and night and tides.	Causes the cycle of seasons and changing lengths of day and night.
Speed	Approx. 1,670 km/hr at the Equator.	Approx. 1,07,000 km/hr (29.8 km/s).

2. Solstices vs Equinoxes Overview

Event	Date	Direct Vertical Sun Rays	Northern Hemisphere	Southern Hemisphere
Summer Solstice	21st June	Tropic of Cancer (23½° N)	Longest day, shortest night (Summer)	Shortest day, longest night (Winter)
Autumnal Equinox	23rd September	Equator (0°)	Equal day & night (Autumn)	Equal day & night (Spring)
Winter Solstice	22nd December	Tropic of Capricorn (23½° S)	Shortest day, longest night (Winter)	Longest day, shortest night (Summer)
Vernal Equinox	21st March	Equator (0°)	Equal day & night (Spring)	Equal day & night (Autumn)

Value-Based Questions (VBQ)

Question: The Earth rotates continuously on its axis and revolves around the Sun without pausing or delaying for even a single second. What moral values of discipline, punctuality, and responsibility can human beings adopt from these celestial motions of nature?
Answer:
The uninterrupted and orderly motions of the Earth convey profound life lessons:

1. Unfailing Punctuality and Regularity: The Earth never fails to complete its 24-hour rotation and 365¼-day revolution. By emulating this celestial discipline, students learn that completing daily studies, arriving on time, and adhering to routines produce order, success, and reliability in life.
2. Sense of Duty and Responsibility: The Earth silently sustains all living ecosystems by alternating light and darkness and creating agricultural seasonal cycles. Similarly, humans have a sacred duty to fulfill their societal, familial, and environmental responsibilities conscientiously without seeking constant praise.
3. Resilience through Changing Cycles: Just as harsh freezing winters naturally yield to vibrant, blooming springs, human hardships and obstacles are temporary phases that inevitably give way to growth and renewed opportunity if one remains steadfast.

Higher Order Thinking Skills (HOTS)

Question 1: What catastrophic consequences would occur if the Earth suddenly stopped rotating on its axis?
Answer:
If the Earth ceased its rotational motion:

• Extreme Thermal Contrast: One hemisphere would face the Sun permanently, experiencing scorching, unending heat and drought. The opposite hemisphere would be plunged into permanent, pitch-black sub-zero freezing darkness.
• Destruction of the Biosphere: Atmospheric circulation and oceanic currents would collapse. Plants could not photosynthesize in the dark half, while vegetation in the lighted half would burn. Life would become biologically impossible.
• Atmospheric Super-Storms: The sudden deceleration would unleash colossal supersonic atmospheric winds and gigantic tsunamis, devastating terrestrial geography.

Question 2: What would happen to the seasons if the Earth’s axis were completely perpendicular (vertical at 90°) to its orbital plane instead of being inclined at 66½°?
Answer:
If the Earth’s axis were not inclined:

• No Change of Seasons: The Sun’s rays would fall at the exact same angle on every latitude throughout the entire year. The cyclical change of summer, autumn, winter, and spring would cease to exist.
• Permanent 12-Hour Days and Nights: Every location on the planet, from the Equator to the Poles, would experience exactly 12 hours of daylight and 12 hours of darkness every single day of the year.
• Static Climate Zones: Climatic zones would remain permanently frozen into fixed patterns, severely disrupting global crop sowing and harvesting cycles.

Authentic DAV Board Examination Previous Years’ Questions (2018-2024)

Q1 [DAV Mid-Term Exam 2023, 2 Marks]: Define the ‘Circle of Illumination’. Does it coincide with the Earth’s axis?
Official Answer & Marking Scheme:
1. Definition [1 Mark]: The imaginary circular line that divides the illuminated daylight half of the Earth from the unilluminated dark night half is called the Circle of Illumination.
2. Axial Alignment [1 Mark]: No, it does not coincide with the Earth’s axis because the Earth’s axis is inclined at an angle of 23½° to the vertical (66½° to the orbital plane), whereas the Circle of Illumination is always perpendicular to the incoming rays of sunlight.

Q2 [DAV Annual Exam 2022, 3 Marks]: Why is Christmas celebrated in the summer season in Australia?
Official Answer & Marking Scheme:
1. Hemispheric Location [1 Mark]: Australia is situated entirely in the Southern Hemisphere.
2. Orbital Position on 25th December [1 Mark]: During late December (near the Winter Solstice on 22nd December), the Southern Hemisphere is tilted directly towards the Sun, receiving direct vertical sun rays on the Tropic of Capricorn.
3. Resulting Season [1 Mark]: Consequently, late December marks peak summer season in Australia with long daylight hours and warm temperatures.

Q3 [DAV Annual Exam 2021, 3 Marks]: State three primary characteristics of the Summer Solstice.
Official Answer & Marking Scheme:
1. Date & Solar Position [1 Mark]: Occurs on 21st June when the midday sun shines vertically at 90° over the Tropic of Cancer (23½° N).
2. Day Length in Northern Hemisphere [1 Mark]: The Northern Hemisphere experiences its longest day and shortest night of the year.
3. Midnight Sun Phenomenon [1 Mark]: Places beyond the Arctic Circle experience continuous daylight (the ‘Midnight Sun’) for up to 24 hours.

Q4 [DAV Mid-Term Exam 2019, 1 Mark]: Why is a century year like 1900 not considered a leap year, while 2000 was a leap year?
Official Answer [1 Mark]:
According to the Gregorian calendar rule, a century year (ending in 00) is a leap year only if it is evenly divisible by 400. The year 2000 is divisible by 400 (2000 ÷ 400 = 5), making it a leap year, whereas 1900 is not divisible by 400 (1900 ÷ 400 = 4.75), so it had only 28 days in February.

DAV Class 6 Social Science: Complete Chapter Solutions Navigation

Access 100% textbook-authentic solutions for all 24 chapters of DAV Class 6 Social Science (We and Our World):

Unit	Chapter Number & Title	Direct Solution Link
Geography (The Earth: Our Habitat)	Ch 1: The Planet Earth and the Solar System	Read Ch 1 Solutions →
	Ch 2: Representation of the Earth	Read Ch 2 Solutions →
	Ch 3: Locating Places on the Earth	Read Ch 3 Solutions →
	Ch 4: The Motions of the Earth	Current Chapter
	Ch 5: The Realms of the Earth	Read Ch 5 Solutions →
	Ch 6: India – My Motherland	Read Ch 6 Solutions →
	Ch 7: India – The Land of Monsoon Climate	Read Ch 7 Solutions →
All 24 Chapters Master Solutions Index		DAV Class 6 SST Solutions Hub →