The Earth moves in two primary motions:
- Rotation (Spinning on its axis)
- Revolution (Orbiting around the Sun)
These motions have significant effects on life, climate, and timekeeping on Earth.
1. Rotation of the Earth
- The Earth rotates on its axis from west to east.
- It completes one full rotation in 24 hours.
- Speed of rotation:
- At the equator: ~1670 km/h.
- Slower at the poles.
Effects of Rotation
✅ Day and Night – One half of the Earth faces the Sun (day), while the other half is in darkness (night).
✅ Coriolis Effect – Winds and ocean currents are deflected due to Earth’s rotation.
✅ Time Zones – The Earth is divided into 24 time zones based on rotation.
✅ Bulging at the Equator – Due to centrifugal force, the Earth is slightly flattened at the poles and bulging at the equator.
2. Revolution of the Earth
- The Earth orbits around the Sun in an elliptical path.
- It completes one revolution in 365.25 days (1 year).
- The average distance from the Sun is 149.6 million km.
Effects of Revolution
✅ Seasons – Due to the tilt of Earth’s axis (23.5°), different parts of the Earth receive varying amounts of sunlight, causing summer, winter, spring, and autumn.
✅ Length of Day and Night – Days are longer in summer and shorter in winter.
✅ Leap Year – The extra 0.25 days every year add up to an extra day every 4 years, making leap years (366 days).
✅ Change in Apparent Position of the Sun – The Sun appears to move north and south throughout the year.
Important Terms Related to Earth’s Motions
1. Perihelion and Aphelion
- Perihelion (Closest to the Sun) – Around January 3rd, the Earth is closest to the Sun (147 million km).
- Aphelion (Farthest from the Sun) – Around July 4th, the Earth is farthest from the Sun (152 million km).
2. Solstices and Equinoxes
- Summer Solstice (June 21) – Longest day in the Northern Hemisphere.
- Winter Solstice (December 21) – Shortest day in the Northern Hemisphere.
- Spring Equinox (March 21) & Autumn Equinox (September 23) – Equal day and night all over the Earth.
MCQs on Motions of the Earth
1. What causes day and night on Earth?
a) Revolution
b) Rotation
c) Sun’s movement
d) Moon’s orbit
Answer: b) Rotation
2. How long does the Earth take to complete one rotation?
a) 12 hours
b) 24 hours
c) 30 days
d) 365 days
Answer: b) 24 hours
3. What is the shape of the Earth’s orbit around the Sun?
a) Circular
b) Elliptical
c) Rectangular
d) Spiral
Answer: b) Elliptical
4. What causes the seasons on Earth?
a) Rotation
b) Revolution and axial tilt
c) Distance from the Sun
d) Ocean currents
Answer: b) Revolution and axial tilt
5. What is the speed of Earth’s rotation at the equator?
a) 500 km/h
b) 1000 km/h
c) 1670 km/h
d) 3000 km/h
Answer: c) 1670 km/h
6. When does the Earth experience equal day and night?
a) Solstices
b) Equinoxes
c) Aphelion
d) Perihelion
Answer: b) Equinoxes
7. Why do we have leap years?
a) Due to the extra 0.25 days per year in Earth’s revolution
b) Because of Earth’s rotation
c) Because of the Moon’s orbit
d) Due to tides
Answer: a) Due to the extra 0.25 days per year in Earth’s revolution
Short Answer Questions
1. What is the difference between rotation and revolution?
- Rotation: Earth spins on its axis in 24 hours, causing day and night.
- Revolution: Earth orbits the Sun in 365.25 days, causing seasons.
2. Why do we experience different seasons?
Seasons occur due to Earth’s axial tilt (23.5°) and revolution around the Sun, which changes the amount of sunlight different parts of Earth receive.
3. What happens on June 21st?
- It is the Summer Solstice in the Northern Hemisphere (longest day).
- It is the Winter Solstice in the Southern Hemisphere (shortest day).
4. Why is the Earth not perfectly spherical?
Due to rotation, the Earth bulges at the equator and is slightly flattened at the poles, making it an oblate spheroid.
Conclusion
The motions of the Earth (rotation and revolution) are responsible for day & night, seasons, time zones, and changes in climate. Understanding these motions helps us in predicting weather patterns, designing calendars, and understanding Earth’s position in space.
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