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Earth, Moon, and the Sun – Class 7 Science Chapter 12 Notes & NCERT PDF

Class 7ScienceChapter 12NCERT book: Curiosity - Science Class 7

Notes and a simple summary of Chapter 12 of the NCERT Class 7 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 12: Earth, Moon, and the Sun

Introduction

In Kanniyakumari, Tamil Nadu, 12-year-old Rashmika notices that coconut-tree shadows are long in the morning and shorter in the afternoon. She thinks the Sun moves across the sky — but she also learnt that the Earth moves around the Sun. Does the Sun move, or does the Earth?

Key Concepts

12.1 Rotation of the Earth

  • On a merry-go-round turning anti-clockwise, surrounding objects seem to move clockwise, entering view on the left and leaving on the right.
  • Likewise, the Sun only appears to move because we watch it from the rotating Earth.
    • Rotation is the motion of an object in which all its parts move in circles around an imaginary line through it — the axis of rotation.
  • Earth's axis passes through the geographic North and South Poles. The Earth completes one rotation in about 24 hours.
  • Seen from above the North Pole, the Earth rotates anti-clockwise — from West to East.
  • With a globe and torch: half the Earth is lit (day), half is dark (night). Sunrise happens when your place moves into light; sunset when it moves into darkness. Eastern India sees sunrise first.
  • Because of rotation from West to East, the Sun, Moon and stars appear to rise in the East and set in the West.
  • The Pole Star (Dhruva Tara) stays nearly fixed because Earth's axis points very close to it; the Big Dipper (Saptarishi) and other stars appear to move around it (Activity 12.3). Long-exposure photos show this as star trails.
  • Foucault pendulum: In the 19th century Leon Foucault used a long pendulum to demonstrate Earth's rotation. A 22-metre Foucault pendulum hangs in the Constitution Hall of the new Parliament building, New Delhi.
  • Aryabhata (Aryabhatiya, about the 5th century CE) explained the apparent westward motion of stars — like a man in a moving boat sees stationary objects moving backward — and gave Earth's rotation time as about 23 h 56 min 4.1 s, very close to today's value.

    • 12.2 Revolution of the Earth

    Revolution is the motion of an object around another object. Its path is its orbit.
  • Seen from the top, Earth's orbit is nearly circular; it completes one revolution in about 365 days and 6 hours.
  • Because Earth revolves, different stars rise at sunset in different months. The Bhil and Pawara communities of the Tapi Valley used star patterns to mark the arrival of the monsoon.

    • Seasons

  • Earth's axis is tilted, and it keeps this tilt while orbiting. The tilt and Earth's spherical shape cause seasons.
  • In June, the Northern Hemisphere tilts towards the Sun: the same sunrays fall on a smaller area (more intense), and daytime is more than 12 hours → summer in the north. In December it is the opposite → winter.
  • Seasons are reversed in the Southern Hemisphere (winter in June, summer in December).
  • Summer solstice ~21 June (longest day in the north); winter solstice ~22 December (shortest day); spring equinox ~21 March and autumn equinox ~23 September (12-hour day).
  • At the North Pole, the Sun rises around 21 March and stays up for six months, setting around 22 September. At the equator, there are always about 12 hours of daylight, so southern Indian states near it feel little seasonal change.
    • Wrong ideas about seasons: that the tilted hemisphere is much closer to the Sun, or that Earth's oval orbit changes its distance a lot. These distance differences are very small — Earth is actually closest to the Sun in January.

    12.3 Eclipses

    Apparent size depends on an object's actual size and its distance. In Activity 12.4, your thumb can cover a friend's head 5 metres away. The Moon is much smaller than the Sun but much closer, so both look about the same size — the Moon can cover the Sun. Mercury and Venus are larger than the Moon but so far away that they appear as tiny dots (a Transit of Venus).

  • Solar eclipse: the Moon comes between the Sun and the Earth, blocking sunlight.

    • - Total solar eclipse: seen from the small area in the Moon's full shadow; it becomes dark for a few minutes. A 'diamond ring' appears as the Moon moves away.

    - Partial solar eclipse: the Moon covers only part of the Sun.

    - Safety: never look at the Sun directly — not even with sunglasses, binoculars or telescopes. Use proper solar eclipse goggles, a projected image (mirror on a sand-filled ball) or events by planetaria/astronomy clubs.

  • Lunar eclipse: the Earth comes between the Sun and the Moon, and Earth's shadow falls on the full Moon.

    • - Total lunar eclipse: the Moon turns dark red.

    - Partial lunar eclipse: only part of the Moon is in Earth's shadow.

    - It is safe to watch with the naked eye.

  • In Sanskrit an eclipse is grahan; the Surya Siddhanta gives methods to predict eclipses. Understanding the cause removes old fears and superstitions.

    • Indian astronomy

  • Kodaikanal Solar Observatory (Palani hills, est. 1899), run by the Indian Institute of Astrophysics, Bengaluru.
  • M.K. Vainu Bappu, father of modern Indian astronomy, set up telescopes at Manora Peak (Nainital) and Kavalur (the Vainu Bappu Observatory), discovered a comet and studied solar eclipses.

    • Activities in the Chapter

  • 12.1 Merry-go-round → surroundings appear to move the opposite way.
  • 12.2 Globe with a sticker and a torch 1.5 m away → rotation, day and night, eastern India's earlier sunrise.
  • 12.3 Sketch the Big Dipper every two hours → stars move around the Pole Star.
  • 12.4 Cover a friend's head with your thumb → apparent size.
  • Teacher set-up: project the Sun's image with a small mirror on a sand-filled ball for safe eclipse viewing.

    • Key Terms

  • Rotation (घूर्णन) — spinning on an axis
  • Axis of rotation (घूर्णन अक्ष)
  • Revolution (परिक्रमण) — motion around another object
  • Orbit (कक्षा) — path of revolution
  • Hemisphere (गोलार्ध) — Northern/Southern half of Earth
  • Equator (भूमध्य रेखा)
  • Solstice (अयनांत) and Equinox (विषुव)
  • Pole Star (ध्रुव तारा), Big Dipper (सप्तर्षि)
  • Solar eclipse (सूर्य ग्रहण), Lunar eclipse (चंद्र ग्रहण)
  • Apparent size (आभासी आकार)
  • Star trails (तारा-पथ)

    • Real-life Connections

  • When it is day in India, it is night in the USA — they are on opposite sides of the rotating Earth.
  • December is summer in Australia — pack summer clothes for a cricket tour there.
  • Tools like the free Stellarium app show upcoming eclipses for your location.

    • Common Misconceptions

  • "The Sun moves around the Earth each day." — Earth's rotation makes the Sun appear to move.
  • "Summer happens when Earth is closest to the Sun." — Seasons come from the tilt and spherical shape; Earth is closest to the Sun in January.
  • "Revolution causes day and night." — Rotation causes day and night.
  • "A lunar eclipse happens when the Sun comes between Earth and Moon." — It is the Earth between the Sun and Moon.
  • "It is safe to look at a solar eclipse with sunglasses." — It can cause blindness; use proper methods.

    • Keep the Curiosity Alive (exercise hints)

  • Stars rise in the East and set in the West; day and night are caused by Earth's rotation.
  • Sunrise happens earlier in Jharkhand than in Gujarat (it is further east).
  • Seeing Orion overhead at 8 pm: the next night it is overhead about 4 minutes earlier (because a rotation is about 23 h 56 min relative to the stars).
  • The same stars rise at midnight on 21 June next year — after one full revolution.
  • A total solar eclipse is seen only where the Moon's small shadow falls, but a lunar eclipse is visible from the whole night side of Earth.
  • With no tilt, there would be no seasons.

    • 💡 Key Learning Points

    • ✓The Earth rotates from West to East in about 24 hours, causing day and night and the apparent rising and setting of the Sun, Moon and stars.
    • ✓The Earth revolves around the Sun in about 365 days and 6 hours, so different stars are seen at night in different months.
    • ✓Seasons are caused by the tilt of Earth's axis and its spherical shape, not by changes in distance from the Sun.
    • ✓A solar eclipse occurs when the Moon blocks sunlight from reaching the Earth; a lunar eclipse when the Earth blocks sunlight from reaching the Moon.
    • ✓The Moon can cover the Sun because apparent size depends on both actual size and distance; never view a solar eclipse directly.

    👨‍🏫 Teaching Tips

    • →Begin with Rashmika's shadow observation and let students measure a stick's shadow in the morning and at noon.
    • →Take students on a merry-go-round (or spin on the spot) to feel how surroundings appear to move the opposite way.
    • →Use a globe, a sticker for your town and a torch in a dark room to show day, night and eastern India's earlier sunrise.
    • →Assign the Big Dipper night-sky sketch at 2-hour intervals as a family activity.
    • →Model seasons by carrying a tilted globe around a lamp while keeping the tilt fixed; shine a torch straight vs slanted on graph paper to show intensity.
    • →Use the thumb-and-head activity to explain apparent size before drawing eclipse diagrams.
    • →Stress eclipse safety and discuss how scientific understanding replaced fear and superstition.

    📋 Assessment Questions

    1. Can the student explain why the Sun appears to rise in the East and set in the West?
    2. Can the student distinguish rotation from revolution and state the time each takes?
    3. Can the student explain seasons using tilt and spherical shape, and reject the distance explanation?
    4. Can the student draw the Sun–Moon–Earth arrangement for solar and lunar eclipses?
    5. Can the student describe safe ways to observe a solar eclipse?

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    Keep learning

    All chapters in Curiosity - Science Class 7

    1. 1. The Ever-Evolving World of Science
    2. 2. Exploring Substances: Acidic, Basic, and Neutral
    3. 3. Electricity: Circuits and their Components
    4. 4. The World of Metals and Non-metals
    5. 5. Changes Around Us: Physical and Chemical
    6. 6. Adolescence: A Stage of Growth and Change
    7. 7. Heat Transfer in Nature
    8. 8. Measurement of Time and Motion
    9. 9. Life Processes in Animals
    10. 10. Life Processes in Plants
    11. 11. Light: Shadows and Reflections
    12. 12. Earth, Moon, and the Sun