Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
Motions of the Earth: NCERT Exercise Solutions
Welcome to the complete NCERT Solutions for Class 6 Social Science Geography Chapter 3 — Motions of the Earth. This chapter explains the two main movements of our planet — rotation and revolution — and how they cause day and night, seasons, and variations in the length of days across the year. Every question from the NCERT textbook exercise is answered here in a clear, exam-focused way, along with additional practice MCQs, common mistakes, and a revision checklist.
How to Use This Page
1. Read the Key Concepts table first for a quick recap of important terms. 2. Work through the Intext Questions to check your understanding as you read the chapter. 3. Study each Chapter-End Exercise answer carefully — these are the exact NCERT questions that appear in exams. 4. Try the MCQ Practice section on your own before looking at the answers. 5. Review Common Mistakes so you don't lose marks on easy questions. 6. Use the Exam Checklist the night before your test to make sure you remember every key point.
Key Concepts (Quick Recap)
| Term | Definition |
|---|---|
| Rotation | The spinning of the Earth on its axis from west to east, completing one turn in approximately 24 hours (one day). |
| Revolution | The movement of the Earth around the Sun along its elliptical orbit, taking 365¼ days (one year) to complete one full round. |
| Axis | An imaginary line running from the North Pole to the South Pole around which the Earth rotates. It is tilted at an angle of 23½° from the vertical. |
| Orbit | The fixed elliptical path along which the Earth (and other planets) move around the Sun. |
| Circle of Illumination | The circular boundary on the Earth that divides the illuminated (day) half from the dark (night) half. It does not coincide with the axis because the axis is tilted. |
| Solstice | A day when one of the poles is tilted at its maximum angle toward or away from the Sun, resulting in the longest or shortest day of the year. |
| Equinox | A day when the Sun is directly overhead at the Equator, making day and night of equal duration (12 hours each) all over the world. Occurs on 21 March and 23 September. |
| Summer Solstice | Occurs on 21 June in the Northern Hemisphere — the North Pole is tilted toward the Sun, giving the longest day and shortest night. |
| Winter Solstice | Occurs on 22 December in the Northern Hemisphere — the North Pole is tilted away from the Sun, giving the shortest day and longest night. |
| Leap Year | A year with 366 days (instead of 365) in which February has 29 days. It occurs every 4 years to account for the extra ¼ day accumulated each year from the 365¼-day revolution period. |
| Elliptical Orbit | The oval-shaped path that the Earth follows around the Sun; the Sun is not at the exact centre but at one focus of the ellipse. |
Intext Questions
Q1. Why do we have day and night on Earth?
Q2. What would happen if the Earth did not rotate on its axis?
- One half of the Earth would always face the Sun and experience continuous daylight and extreme heat.
- The other half would always face away from the Sun and experience continuous darkness and extreme cold.
- There would be no day-and-night cycle, making most of the planet uninhabitable.
- Temperature differences between the two halves would create violent winds and weather extremes.
Q3. What is the difference between rotation and revolution?
| Aspect | Rotation | Revolution |
|---|---|---|
| Meaning | Spinning of the Earth on its own axis | Movement of the Earth around the Sun |
| Duration | About 24 hours (1 day) | 365¼ days (1 year) |
| Direction | West to east | West to east (counter-clockwise when viewed from above the North Pole) |
| Effect | Causes day and night | Causes seasons and variation in day length |
| Path | On its axis | Along its elliptical orbit around the Sun |
Q4. Why does a leap year have 366 days?
Q5. Why are the seasons different in the Northern and Southern Hemispheres?
Chapter-End Exercise Questions
Q1. What is the angle of inclination of the Earth's axis with its orbital plane?
Q2. Define rotation and revolution.
- Rotation: Rotation is the movement of the Earth on its own axis. The Earth rotates from west to east (anti-clockwise when viewed from the North Pole). It takes approximately 24 hours to complete one rotation. Rotation causes the cycle of day and night on Earth.
- Revolution: Revolution is the movement of the Earth around the Sun in an elliptical orbit. It takes 365¼ days to complete one revolution. Revolution, combined with the tilt of the Earth's axis, causes seasons and changes in the length of day and night at different times of the year.
Q3. What is a leap year?
Why it exists: The Earth takes 365¼ days to complete one revolution around the Sun. The extra ¼ day each year accumulates over four years:
- ¼ day × 4 years = 1 extra day
This extra day is added to the calendar every fourth year, making it a leap year with 366 days. Leap years are divisible by 4 (e.g., 2024, 2028). However, century years like 1900 are not leap years unless divisible by 400 (so 2000 was a leap year, but 2100 will not be).
Q4. Differentiate between the summer solstice and the winter solstice.
| Aspect | Summer Solstice | Winter Solstice |
|---|---|---|
| Date (Northern Hemisphere) | 21 June | 22 December |
| Sun's position | Sun is directly overhead at the Tropic of Cancer (23½°N) | Sun is directly overhead at the Tropic of Capricorn (23½°S) |
| Tilt | North Pole is tilted toward the Sun | North Pole is tilted away from the Sun |
| Day length (Northern Hemisphere) | Longest day, shortest night | Shortest day, longest night |
| Day length (Southern Hemisphere) | Shortest day, longest night | Longest day, shortest night |
| Season (Northern Hemisphere) | Summer | Winter |
| Season (Southern Hemisphere) | Winter | Summer |
Q5. What is an equinox? Why are the days and nights equal on 21 March and 23 September?
Why days and nights are equal on 21 March and 23 September:
On these two dates, neither pole is tilted toward or away from the Sun. The Earth's axis is oriented such that the circle of illumination passes through both poles, dividing every latitude into two equal halves — one in daylight and one in darkness. As a result, every place on Earth experiences exactly 12 hours of daylight and 12 hours of darkness.
- 21 March is called the Vernal (Spring) Equinox in the Northern Hemisphere.
- 23 September is called the Autumnal Equinox in the Northern Hemisphere.
Q6. Why does the Southern Hemisphere experience winter and summer solstice at different times than the Northern Hemisphere?
- When the Northern Hemisphere is tilted toward the Sun (21 June), it receives more direct sunlight and experiences summer. At the same time, the Southern Hemisphere is tilted away from the Sun, receiving less direct sunlight and experiencing winter.
- When the Northern Hemisphere is tilted away from the Sun (22 December), it experiences winter. At the same time, the Southern Hemisphere is tilted toward the Sun and experiences summer.
Thus, the summer solstice in the Southern Hemisphere falls on 22 December (when the Northern Hemisphere has its winter solstice), and the winter solstice in the Southern Hemisphere falls on 21 June (when the Northern Hemisphere has its summer solstice).
Q7. Why do the poles experience about six months of day and six months of night?
- From 21 March to 23 September (about six months), the North Pole is tilted toward the Sun. During this entire period, the North Pole receives continuous sunlight and experiences six months of day. Simultaneously, the South Pole is tilted away from the Sun and experiences six months of night.
- From 23 September to 21 March (about six months), the situation reverses. The North Pole is tilted away from the Sun and experiences six months of night, while the South Pole is tilted toward the Sun and experiences six months of day.
This happens because the tilt ensures that one pole remains above the circle of illumination for half the year and below it for the other half.
Q8. Fill in the blanks
(a) The Earth moves around the Sun in an elliptical orbit.
(b) The Earth completes one rotation in about 24 hours.
(c) On 21 March and 23 September, days and nights are equal all over the world.
(d) On 21 June, the Northern Hemisphere is tilted toward the Sun.
(e) The angle of inclination of the Earth's axis with the orbital plane is 66½°.
Q9. True or False
Q10. Match the Column
| Column A | Column B |
|---|---|
| (i) Rotation | (c) Spinning of the Earth on its axis |
| (ii) Revolution | (e) Movement of the Earth around the Sun |
| (iii) Equinox | (a) Equal day and night on 21 March and 23 September |
| (iv) Summer Solstice | (d) Longest day in the Northern Hemisphere on 21 June |
| (v) Leap Year | (b) Year with 366 days |
MCQ Practice
Choose the correct option for each question. The correct answer is marked with (✓).
Common Mistakes to Avoid
1. Confusing 23½° and 66½°: The angle of tilt of the Earth's axis from the vertical is 23½°, while the angle of the Earth's axis with the orbital plane is 66½°. Students often mix up these two values. Remember: 23½° + 66½° = 90°.
2. Writing "east to west" for rotation direction: The Earth rotates from west to east. This is why the Sun appears to rise in the east and set in the west. Do not write "east to west" for the direction of rotation.
3. Confusing solstice dates: 21 June is the summer solstice in the Northern Hemisphere (longest day), and 22 December is the winter solstice (shortest day). Do not swap these dates.
4. Thinking equinox means equal day and night everywhere always: Equinox means equal day and night only on 21 March and 23 September. On other dates, the lengths of day and night are not equal — they vary depending on latitude.
5. Forgetting that seasons are opposite in the two hemispheres: When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, and vice versa. Always specify which hemisphere you are referring to.
6. Confusing rotation and revolution: Rotation causes day and night (24-hour cycle). Revolution causes seasons (365¼-day cycle). Do not mix up their effects in exam answers.
Exam Checklist
Before your exam, make sure you can answer each of these:
- [ ] What is rotation? State its direction, duration, and effect.
- [ ] What is revolution? State its duration, path, and effect.
- [ ] What is the angle of inclination of the Earth's axis with its orbital plane? (66½°)
- [ ] What is the angle of tilt from the vertical? (23½°)
- [ ] What is a leap year? Why does it occur? How is the extra ¼ day accounted for?
- [ ] What is an equinox? On which two dates does it occur?
- [ ] Differentiate between summer solstice and winter solstice (date, Sun's position, day length, season).
- [ ] Why do the poles experience six months of day and six months of night?
- [ ] Why are seasons opposite in the Northern and Southern Hemispheres?
- [ ] What is the circle of illumination? How does it relate to day and night?
Tip for exams: Always draw a neat, labelled diagram showing the Earth's tilt, its orbit around the Sun, and the positions during solstices and equinoxes. Diagrams carry marks and help you explain your answers clearly.