Class 7 Science Chapter 12: Earth, Moon, and the Sun | Rotation, Revolution, Day–Night Cycle, Phases of the Moon, Eclipses & Orbits Explained
Complete Chapter 12 guide: Earth’s rotation (west to east) and 24‑hour day, day–night with globe–torch activity, revolution and year length, seasons overview, phases of the Moon and why only one side is seen, basic idea of solar and lunar eclipses, Foucault pendulum evidence of Earth’s rotation, plus NCERT-style activities, diagrams and exam questions for CBSE
Updated: 6 months ago
Earth, Moon, and the Sun
Class 7 Science Chapter 12 | Complete NCERT Guide | Earth's Rotation, Apparent Sun Motion, Day-Night Cycle, Shadows 2025
Full Chapter Summary & Detailed Notes - Earth, Moon, and the Sun
Introduction – Rashmika’s Observation
The chapter opens with a beautiful real-life story of Rashmika, a 12-year-old girl in Kanniyakumari, Tamil Nadu. While cycling to school in the morning, she notices that the shadows of coconut trees are very long. On her way back in the afternoon, the same shadows are much shorter. She wonders:
“Why do shadows change their length? Is it because the Sun is moving across the sky?”
But she remembers from Grade 6 (chapter “Beyond Earth”) that the Earth moves around the Sun. So she gets puzzled: Does the Sun move? Or does the Earth move? This question becomes the central theme of the entire chapter.
12.1 Rotation of the Earth – The Real Reason
We all see the Sun “rising” in the East and “setting” in the West every day. But actually, the Sun is almost stationary. It only appears to move because the Earth is rotating (spinning) on its own axis.
Activity 12.1: Let us explore – The Merry-Go-Round Experiment
This is the most important activity of the chapter and is asked in almost every exam.
- Sit on a merry-go-round facing outward.
- Ask someone to rotate it slowly in the anti-clockwise direction.
- Observation 1: All stationary objects (trees, buildings, people) around you appear to move in the opposite direction — clockwise direction.
- Observation 2: Fix your gaze on one tree. It appears to come from your left side, move across in front of you, and disappear on your right side.
Conclusion from Activity: When the observer (you) rotates anti-clockwise, stationary objects appear to move clockwise. Exactly the same thing happens on Earth!
Applying the Merry-Go-Round Logic to Earth
- Earth rotates from West to East (anti-clockwise if seen from above North Pole).
- Because of this rotation, the stationary Sun appears to move from East to West.
- That is why the Sun “rises” in the East and “sets” in the West.
Major Effects of Earth’s Rotation
| Effect | Explanation |
|---|---|
| Day and Night | Earth takes 24 hours for one rotation. The side facing Sun → Day; opposite side → Night. |
| Changing Length of Shadows | Morning/Evening: Sun low → long shadows Noon: Sun overhead → shortest shadows (Rashmika’s observation) |
| Apparent Motion of Sun & Stars | All celestial objects appear to move East to West daily. |
Important Facts about Rotation
- Time period: 24 hours (1 day)
- Direction: West to East
- Axis: Imaginary line from North Pole to South Pole (tilted 23.5° – causes seasons, but not in this chapter)
- Speed: ~1670 km/h at equator, but we don’t feel it (constant speed + gravity)
Scientific Proofs of Earth’s Rotation
- Foucault’s Pendulum (1851): Pendulum swing direction changes slowly → Earth rotates beneath it.
- Coriolis Effect: Moving objects (winds, missiles) deflect right in Northern Hemisphere, left in Southern.
- Satellite Images: Direct visual proof of spinning Earth.
Common Mistakes & Clarifications
- Day-night is caused by rotation (24 hrs), not revolution.
- Seasons are caused by revolution + axial tilt (365 days).
- We don’t feel rotation because speed is constant and atmosphere rotates with us.
Key Takeaways for Exams
| Concept | One-Liner Answer |
|---|---|
| Why does the Sun appear to rise in East & set in West? | Due to Earth’s rotation from West to East |
| Activity 12.1 conclusion? | Merry-go-round anti-clockwise → objects appear clockwise → same as Earth’s rotation makes Sun appear to move East to West |
| Shadow length change? | Morning & evening long, noon shortest |
| Time for one rotation? | 24 hours |
| Direction of rotation? | West to East |
Golden Exam Answer (Write this in every 3/5 mark question)
“The Sun appears to rise in the east and set in the west because the Earth rotates on its axis from west to east. This rotation takes 24 hours and also causes day and night as well as the change in length of shadows during the day.”
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