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A common explanation for summer, even among adults, is that the Earth is closer to the Sun. The new Class 7 science book lists this as one of the incorrect reasons often given, and shows why it is wrong. Chapter 12 also explains why the Sun seems to move, why the night sky changes over the year, and how eclipses happen. This guide takes you through each idea, with worked examples that use the chapter's own numbers.
What does Chapter 12 of Class 7 Curiosity cover?
Earth, Moon, and the Sun is Chapter 12 of NCERT's *Curiosity* for Grade 7 (first edition April 2025, reprint 2026-27). It covers:
Rotation: the Earth spins on its axis from west to east in about 24 hours, causing day and night and the apparent motion of the Sun, Moon and stars.
The Pole Star and the Big Dipper, and why stars appear to circle the Pole Star.
Revolution: one trip round the Sun takes about 365 days and 6 hours, and the night sky changes through the year.
Seasons, solstices and equinoxes.
Solar and lunar eclipses, and how to watch a solar eclipse safely.
Why does the Sun seem to move across the sky?
Because we are standing on a spinning Earth. The chapter uses a merry-go-round: turn anticlockwise and the trees around you seem to turn clockwise. Seen from above the North Pole, the Earth turns anticlockwise, which is west to east. So the Sun, Moon and stars appear to rise in the east and set in the west.
Worked example: who sees sunrise first? Gujarat is in the west of India and Jharkhand is further east. The Earth turns from west to east, so places further east turn into sunlight first. Sunrise happens earlier in Jharkhand than in Gujarat. (The chapter has this as a true-or-false statement; now you know the answer and the reason.)
Why do seasons happen?
The chapter gives two reasons that work together. The Earth's axis is tilted, and the Earth keeps that tilt as it goes round the Sun. In June the Northern Hemisphere leans towards the Sun, so:
The same amount of sunlight falls on a smaller area, so each part of the ground is heated more.
Days are longer than 12 hours.
More intense sunlight for longer gives summer. In December it is the other way round. In the Southern Hemisphere the seasons are reversed, which is why a cricket team touring Australia in December packs for summer.
Worked example: how much does distance change? The chapter's project has you draw two circles with radii 14.7 cm and 15.2 cm, where 1 cm stands for 10 million km.
Closest distance: 14.7 × 10 million = 147 million km.
Farthest distance: 15.2 × 10 million = 152 million km.
Difference: 152 − 147 = 5 million km, which is 5 ÷ 152 ≈ 0.033, or about 3% of the farthest distance.
On paper, the two circles are only half a centimetre apart. That small change cannot explain the big difference between summer and winter.
Worked example: why leap years? One revolution takes about 365 days and 6 hours. Four years leave 4 × 6 = 24 extra hours, which is one whole day. That is why a calendar adds a day every fourth year.
How do solar and lunar eclipses happen?
Solar eclipse: the Moon comes between the Sun and the Earth and blocks sunlight from reaching part of the Earth. The Moon is much smaller than the Sun but much closer, so it can look the same size. The chapter shows this with your thumb: held at arm's length, it can cover a friend's head 5 metres away. Where the Moon's shadow falls, people see a total eclipse for a few minutes; nearby, they see a partial one.
Lunar eclipse: the Earth comes between the Sun and the Moon, and the Earth's shadow falls on the full Moon. In a total lunar eclipse the Moon turns dark red.
Why not every month? NASA explains that it only happens occasionally because the Moon does not orbit in the same plane as the Sun and Earth, so most months the Moon passes a little above or below the line.
Safety. You can watch a lunar eclipse with your naked eye. Never look straight at the Sun during a solar eclipse. NASA's eclipse safety guidance says regular sunglasses, however dark, are not safe; eclipse glasses should meet the ISO 12312-2 standard; and a pinhole projector is a simple indirect method. The chapter adds: do not use binoculars or telescopes, and join an event run by a planetarium or astronomy club if you can.
What do students get wrong about the sky?
Astronomy ideas are hard for nearly everyone. Lelliott and Rollnick (2010) reviewed 103 research articles from 1974 to 2008 and concluded that the day-night cycle is fairly well understood, especially by older students, while Moon phases, the seasons and gravity are concepts most people find difficult to understand and explain.
The common slips:
"Summer is when the Earth is closest to the Sun." No; see the worked example.
"The Sun goes round the Earth every day." The Earth rotates; the Sun's movement is apparent.
"Day and night come from the Earth going round the Sun." That is revolution; day and night come from rotation.
"A lunar eclipse is when the Sun is between the Earth and the Moon." It is the Earth in the middle.
"Eclipses can be watched safely through sunglasses." They cannot.
A one-week practice plan
Day 1: With a globe or ball and a torch in a dark room, find day and night, then tilt the ball and move it round the torch.
Day 2: Draw the two-circle diagram from the worked example.
Day 3: On a clear evening, sketch the Big Dipper with the time, then again two hours later.
Day 4: Draw solar and lunar eclipse diagrams with the Sun, Earth and Moon in the right order.
Day 5: Answer the chapter questions from memory, then check.
The chapter builds on shadows and light in Chapter 11, and our profile of Arthur Eddington and the 1919 eclipse shows what scientists learn from eclipses. If tilt and sunlight are hard to picture, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read.
Tonight, tilt a ball in front of a torch and find where the light is most concentrated.
