NCERT Solutions for Class 7 Science Chapter 12 Earth Moon and the Sun (PDF) – 2027

The Earth moves. The Earth rotates (spins) on its own axis from West to East, once in about 24 hours. Because we watch the sky from this rotating Earth, the Sun only appears to move across the sky from East to West — just as trees seem to move past us when we ride a merry-go-round.

Because the Earth rotates on its axis from West to East. As the Earth carries us eastward, the Sun comes into our view on the eastern side (sunrise) and later goes out of view on the western side (sunset). So the Sun only appears to move from East to West.

It is the Earth that is turning; the Sun only appears to move. Just as trees and buildings seem to move the opposite way when we ride a merry-go-round, the Earth’s rotation from West to East makes the Sun appear to move across the sky from East to West.

Yes, the objects around appear to move. They appear to move in the clockwise direction — opposite to the anti-clockwise turning of the merry-go-round.

The tree appears to turn around you in the clockwise direction — opposite to your anti-clockwise turning. No, it is not in view all the time. It appears on your left-hand side, moves across in front of you and goes out of view on your right-hand side; it comes back into view only after some time.

The Earth spins about its axis of rotation — an imaginary line passing through its geographic North Pole and South Pole. Viewed from above the North Pole, the Earth rotates in the anti-clockwise direction, that is, from West to East, completing one rotation in about 24 hours.

Observation: the sticker moves along a circle around the axis and, after one complete turn, comes back to its starting position — this is one rotation. Every part of the globe moves in a circle around the axis; only the North Pole and the South Pole, which lie on the axis, stay in place.

Yes. The half of the globe facing the torch is lit and the other half stays dark. The lit half has day and the dark half has night.

The light falls on the eastern part of India first when the globe rotates from West to East about its North–South axis (anti-clockwise when seen from above the North Pole). If the globe is turned the other way, the light reaches western India first, which does not happen in reality.

Yes. In every turn of the globe, the sticker goes through one full cycle: it moves into the light (sunrise), stays in the lit half (day), moves into the dark (sunset) and stays in the dark half (night). So the Earth’s rotation causes day and night.

Yes — you would observe exactly what the girl in Fig. 12.6 observes. Standing on the equator facing North, your right hand points East and your left hand points West, and the Sun runs from right to left across the sky.

Yes, indeed — the stars also appear to move. Because the Earth rotates from West to East, the stars appear to rise in the East and set in the West, just like the Sun. Stars such as the Big Dipper (Saptarishi) appear to move around the Pole Star, which looks almost fixed because the Earth’s axis points very close to it.

Yes, the Big Dipper has moved. After two hours it is seen at a different place in the sky, and its orientation (tilt) has also changed. Draw it again against the same tree or building and write the time beside the sketch. (In Fig. 12.7 it moves from low in the Northeast at 7 pm to higher up at 9 pm.)

Yes. Put all your sketches side by side and the Big Dipper is seen to travel along a large arc of a circle, rising in the Northeast, curving over the North, and setting towards the Northwest. The centre of that circle is the Pole Star.

Because the Earth is also revolving around the Sun. As it moves along its orbit, the night side of the Earth faces a different part of the sky in different months — so a different set of stars is on show after sunset.

Yes — but the revolution alone is not enough. Seasons happen because of the revolution together with two other facts: the Earth’s axis of rotation is tilted with respect to its orbit, and the Earth is spherical.

No. The two planets, Mercury and Venus, are bigger than the Moon but are much farther from us, so their apparent size is very small compared with the Sun and they cannot block its light. When Venus passes between the Sun and the Earth, it looks only like a tiny black dot on the Sun (Transit of Venus). Only the Moon, which is much closer, can block the Sun.

Yes. With one eye closed and the arm stretched out, the thumb can cover the whole head of a friend standing about 5 metres away, even though the thumb is much smaller. The thumb is much closer to the eye, so its apparent size (the size as seen by the eye) is about the same as that of the head.

Key idea: in rotation, every part of an object moves in a circle, and all these circles are centred on one imaginary line passing through the object — the axis of rotation. The Earth rotates about the axis through its North and South Poles; the poles themselves stay in place.

Both reasons are wrong. In both cases the change in the Earth’s distance from the Sun is very small, so it cannot cause seasons. In fact, the Earth is closest to the Sun in January, when the Northern Hemisphere has winter. Seasons are caused by the tilt of the Earth’s axis and its spherical shape.

These four dates are the milestones of the year. Learn them as a table.

Key idea: how big an object looks (its apparent size) depends on its actual size and its distance from us. Mercury and Venus are bigger than the Moon but much farther away, so they look like tiny dots and cannot block the Sun. The Moon is small but very close, so it can cover the Sun.

This is the safe way to watch a solar eclipse — you look at a picture of the Sun on a wall, never at the Sun itself. Here is how to build and use it.

Key idea: the Sun and the planets pull on each other, so they all move around a common point that is very close to the Sun’s centre. So the Sun also wobbles a little. A star that has planets wobbles in the same way, and scientists use such tiny wobbles to discover planets around other stars (exoplanets).

Stellarium is a free planetarium program for a computer. It draws the sky exactly as it will look from any place, on any date, at any time — so you can find out in advance which eclipses will be visible from your own town.

M.K. Vainu Bappu (1927–1982) is called the father of modern Indian astronomy because he built the facilities on which Indian astronomy still stands.

North Pole: 0 hours of sunlight (it stays dark for all 24 hours). South Pole: 24 hours of sunlight.

She will see Orion overhead at nearly 8 pm today — in fact about 4 minutes earlier, at about 7:56 pm.

The Earth completes one rotation in about 24 hours, so the stars return to nearly the same position at nearly the same time every night. Because the Earth also moves a little along its orbit each day, the stars reach the same place about 4 minutes earlier each day.

She will see the same group of stars rising at midnight on about 21 June next year.

Because the Earth revolves around the Sun, the stars seen at a given time of night change through the year. The Earth returns to the same position in its orbit after one revolution (about 365 days), so the same stars rise at midnight on about the same date every year.

Because the Earth is a sphere and sunlight can light only one half of it at a time. India and the USA lie on opposite sides of the globe, so when India is in the lit half, the USA is in the dark half.

Adithya — option (iii) — was being careless. Looking at the Sun directly, even during an eclipse, can damage the eyes and cause blindness. The other three used safe methods: eclipse goggles, a mirror projecting the Sun’s image on a screen, and a planetarium programme with proper eye protection.

Remember the one rule that decides both rows: the body that causes the eclipse always stands in the middle.

Because what matters is the apparent size — how big an object looks — and this depends on both its actual size and its distance from us. The Moon is much smaller than the Sun, but it is also much closer to us. So the Moon and the Sun look about the same size in the sky, and the Moon can cover the Sun completely.

They should pack summer clothes. December is summer in Australia, even though it is winter in India.

The Moon is small, so its dark shadow covers only a small area of the Earth’s surface. Only people in that area see a total solar eclipse; people around it see a partial one. In a lunar eclipse, the much bigger Earth’s shadow covers the whole Moon, so the eclipsed Moon can be seen by everyone on the night side of the Earth — a large part of the Earth.

There would be no seasons. If the axis were not tilted, neither hemisphere would ever lean towards the Sun. Every place would get sunlight of the same intensity all through the year, and day and night would be about 12 hours each everywhere on every day. So each place would have nearly the same weather throughout the year.

Keep the globe’s axis tilted in the same direction at every position around the lamp — do not turn it to face the lamp. Sample observations:

(i) How much of each hemisphere is lit

(ii) and (iii) Length of day and night at different positions

The difference is only 0.5 cm on paper — about 3% of the distance. The two circles almost overlap, so the Earth’s orbit is very nearly a circle, and this small change in distance cannot cause seasons.

Yes — a bigger tilt would make the seasons far more extreme, and Uranus is the spectacular proof of it.