Science · Class 7 · Chapter 12

Earth, Moon, and the Sun

• Rotation — Earth spinning on its own axis (~24 hours).
• Axis of rotation — The imaginary line through the poles.
• Revolution — Earth's motion around the Sun (~365¼ days).
• Orbit — The path followed while revolving.
• Solstice — Day of longest or shortest daylight.
• Equinox — Day when daytime and night are equal.
• Solar eclipse — Moon blocks sunlight from reaching Earth.
• Lunar eclipse — Earth blocks sunlight from reaching the Moon.

Chapter 12 · Concept 1 of 10

The Rotation of the Earth

• Like a merry-go-round rider seeing the world seem to spin the opposite way, the Sun appears to move across our sky because the Earth itself is spinning.
• One rotation, ~24 hours — The Earth spins on its axis — an imaginary line through the North and South Poles — completing one full turn about every 24 hours, West to East.

Chapter 12 · Concept 2 of 10

Day and Night

• Half lit, half dark — The half of Earth facing the Sun has daytime; the other half has night.
• East to West — Because Earth spins West to East, the Sun (and Moon and stars) appear to rise in the East and set in the West.

Chapter 12 · Concept 3 of 10

Why the Pole Star Stays Put

• Pointing at a fixed spot — Earth's axis points almost exactly at the Pole Star, so it appears nearly stationary while other stars circle around it — captured in long-exposure photos as star trails.
• Aryabhata's insight — This ancient Indian astronomer described this apparent motion and calculated Earth's rotation period remarkably close to today's accepted value.

Chapter 12 · Concept 4 of 10

The Revolution of the Earth

• Revolution is the motion of an object around another — the path it follows is called its orbit.
• One trip, ~365¼ days — The Earth revolves around the Sun in a nearly circular orbit — and as it does, the stars visible after sunset gradually change through the year.

Chapter 12 · Concept 5 of 10

What Really Causes the Seasons

• A tilted axis — Earth's axis stays tilted throughout its orbit. In June, the Northern Hemisphere tilts toward the Sun (summer); in December, it tilts away (winter).
• Not about distance — Earth is actually closest to the Sun in January — the tilt and shape of the Earth cause seasons, not distance.

Chapter 12 · Concept 6 of 10

Solstices and Equinoxes

• Event | Around | What happens
• Summer solstice — 21 June — Longest day in the Northern Hemisphere
• Winter solstice — 22 December — Shortest day in the Northern Hemisphere
• Equinoxes — 21 March, 23 September — Day and night each about 12 hours

Chapter 12 · Concept 7 of 10

Solar Eclipse

• Same apparent size, different distance — The Moon is far smaller than the Sun, but also far closer to Earth — so it can appear to just cover the Sun completely.

Chapter 12 · Concept 8 of 10

Total and Partial Solar Eclipses

• Total vs partial — A total eclipse fully blocks the Sun in a small area; a partial eclipse blocks only part of it over a wider area.
• Safety first — Never look directly at the Sun during an eclipse, even with sunglasses or binoculars — use proper eclipse-viewing methods, like a mirror projection.

Chapter 12 · Concept 9 of 10

Lunar Eclipse

• Safe to watch — Earth's shadow falls on the Moon — this is completely safe to view directly with the naked eye.

Chapter 12 · Concept 10 of 10

Solar vs Lunar Eclipse

• | Solar eclipse | Lunar eclipse
• What blocks what — Moon blocks the Sun — Earth's shadow falls on the Moon
• Visible from — A small area on Earth — A large part of Earth's night side
• Safe to view directly? — No — Yes

Quick Recap

Check Your Understanding

1. 1During one Earth rotation, how many hours of sunlight do the North Pole and South Pole each receive?
2. 2Fill in the blanks: (i) Stars rise in the ___ and set in the ___. (ii) Day and night are caused by Earth's ___. (iii) When the Moon fully covers the Sun, it's called a ___ solar eclipse.
3. 3Padmashree saw Orion nearly overhead at 8 pm yesterday. When will she see it overhead today?