NCERT Solutions Class 7 Science Chapter 12 Earth Moon and the Sun

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 7 · SCIENCE

NCERT Solutions

Chapter 12: Earth, Moon, and the
Sun

NCERT Textbook — Curiosity

BOOK PAGES SECTIONS QUESTIONS MEDIUM

169 – 186 17 41 English

Solutions, notes, sample papers & more at 43 pages

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

CLASS 7 · SCIENCE · CURIOSITY

NCERT Solutions — Chapter 12: Earth, Moon, and the
Sun
Complete NCERT Solutions for Class 7 Science Chapter 12 Earth, Moon, and the Sun from the NCERT
textbook Curiosity. Every question is answered — Activities 12.1 to 12.4, all six Dive Deeper boxes, the
Science and Society and Know a Scientist boxes, every in-text and speech-bubble question from pages 169
to 180, all twelve Let Us Enhance Our Learning exercises and the three Exploratory Projects — with the
figures of the chapter read off the printed page, not guessed.

TEXTBOOK BOOK PAGES

Curiosity (Class 7) 169 – 186

SECTIONS QUESTIONS

17 41

MEDIUM

English

In-text Question — Page 169
Chapter opener — Rashmika's puzzle

Q1 She wondered — does the Sun move in the sky? Or does the Earth move?

The Earth moves. The Sun only appears to move across the sky because we watch it from an
Earth that is spinning.
Rashmika saw two things and could not fit them together. She saw the coconut-tree shadows
change length through the day, which made her think the Sun travels across the sky. She had
also learnt in Grade 6 that the Earth goes around the Sun. Both observations are real; the
missing piece is the Earth's rotation — its spin on its own axis, once in about 24 hours.

Why it happens: when you sit on a merry-go-round turning anti-clockwise, the trees
around you seem to swing past in the clockwise direction. You are moving, not the
trees. In exactly the same way, the Earth turns from West to East, so the Sun appears
to come up in the East, cross the sky and go down in the West. That changing
direction of the Sun is what makes shadows long in the morning, short near noon,
and long again by evening.

Page 1 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Two different motions: the Earth rotates on its axis (about 24 hours — this gives
day and night) and it revolves around the Sun (about 365 days and 6 hours — this
gives the year and, with the tilt, the seasons). Rashmika had remembered the
second one and forgotten the first.

In-text Questions — Page 170
12.1 Rotation of the Earth

Q1 You might have also noticed that the Sun rises in the East and sets in the West.
Have you ever wondered why?

Because the Earth rotates from West to East. Anything fixed in the sky therefore seems to move
the opposite way — from East to West.
Picture a place on the equator at dawn. As the Earth turns eastward, that place swings into the
sunlight from the dark side, and the Sun appears to climb up on the eastern horizon. Twelve
hours later the same place turns out of the sunlight, and the Sun appears to slip below the
western horizon.

rotation: West → East

Day Night

Sun sunset sunrise

Sunlight always lights one half of the Earth. As the Earth turns from West to East, a place first crosses
into the lit half (sunrise) and later crosses out of it (sunset).

Page 2 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Check it yourself: hold a ball in a beam of torchlight in a dark room and turn the
ball slowly anti-clockwise when seen from the top. A dot marked on the ball moves
into the light and out of it — one rotation, one day and one night.

Q2 When we view from the Earth, the Sun appears in the East, moves across the sky
from the East to the West and disappears in the West. Does it indicate that the Sun
is moving in the sky? Or might it be that the Earth itself is turning around and the
Sun just appears to move?

The second one is correct — the Earth is turning around, and the Sun only appears to
move.
The merry-go-round of Activity 12.1 settles it. Sitting on a merry-go-round that turns anti-
clockwise, you see every tree and building swing past you in the clockwise direction, entering
your view on the left and leaving it on the right. You know perfectly well that the trees are not
moving — you are.
Our situation on the Earth is the same, only slower and much larger. The Earth carries us around
once in about 24 hours, from West to East, so the Sun enters our view in the East and leaves it in
the West.

Why it happens: motion is always judged with respect to something. Since we
cannot feel the Earth's smooth spin, we naturally credit the motion to the Sun. This is
called apparent motion — the Moon and the stars show it too, and for exactly the
same reason.

Did you know? Aryabhata explained this in the fifth century CE with a boat: a man
moving forward in a boat sees the stationary bank slipping backwards. He even gave
the length of one rotation as about 23 hours 56 minutes 4.1 seconds — remarkably
close to the value accepted today.

Activity 12.1: Let us explore — Page 170

Page 3 of 43

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Class 7 Science Chapter 12 Earth, Moon, and the Sun
a g l AglaSem · NCERT Solutions

12.1 Rotation of the Earth
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ACTIVITY

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Yes, everything around you appears
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Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Why this matters for the chapter: replace the merry-go-round by the Earth and the
tree by the Sun. The Earth turns anti-clockwise as seen from above the North Pole,
so for a person on the equator the Sun appears on the left-hand (eastern) side,
crosses the sky, and disappears on the right-hand (western) side. The time when it is
out of view is night, and the whole cycle takes about 24 hours.

Tip: do this activity slowly and with someone holding the merry-go-round steady. If
you feel giddy, stop and look at a fixed point on the ground.

In-text Question — Page 171
12.1 Rotation of the Earth

Q1 In which way is the Earth turning around itself?

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.
It spins in space just as a top spins about its spindle, a ceiling fan about its shaft, or a ball spun
on a fingertip (Fig. 12.2).

QUESTION ABOUT THE SPIN ANSWER

About what line? The axis of rotation, through the North Pole and the South Pole

In which sense? Anti-clockwise when viewed from above the North Pole

In which compass direction? From West to East

How long for one rotation? About 24 hours

Tip: the direction is easy to remember from an everyday fact — the Sun rises in the
East. A place must turn towards the East to meet the sunlight first, so the Earth turns
West to East.

Activity 12.2: Let us explore — Pages 171 and 172

Page 5 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

12.1 Rotation of the Earth

ACTIVITY

Q1 While viewing from above the North Pole, slowly rotate the globe on its axis in anti-
clockwise direction. Observe how your location turns around and finally comes back
to its original position completing one rotation.

Stick a small paper sticker on the globe at your own town. Now look down on the globe from
straight above the North Pole and turn it slowly anti-clockwise.
Observation: the sticker does not go up or down — it travels along a circle, parallel to the
equator, and after one complete turn it arrives back exactly where it started. Every other point of
the globe does the same thing on its own circle, and all these circles have their centres on the
axis.

Why it happens: that is precisely what rotation means — all parts of the object
move in circles about an imaginary line passing through it. The two points that do
not travel at all are the North Pole and the South Pole, because they lie on the axis.

Try this: stick a second sticker near the equator and a third close to the North Pole.
In one turn both complete a full circle in the same time, but the equator sticker
covers a much bigger circle — so a place on the equator is actually racing through
space much faster than a place near the pole.

Page 6 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q2 Now, shine light from the torch placed at some distance, say 1.5 metres, on the
globe as shown in Fig. 12.4b. Do you notice how half of the globe receives the light
from the torch, while the other half stays dark?

Fig. 12.4(b), page 172 — a torch about 1.5 m from a globe standing on a board, in a
darkened room. Redrawn sketch.

Yes. With the torch acting as the Sun and the room dark, exactly one half of the globe is lit and
the other half stays dark, and the boundary between them is a circle running through both
poles' side of the globe.

HALF OF THE GLOBE WHAT IT REPRESENTS

The half facing the torch Daytime

The half turned away from the torch Night-time

Why it happens: light travels in straight lines and the Earth is an opaque sphere. A
sphere can present only half of its surface to a distant source at any instant; the rest
is in its own shadow. Since the real Sun is very far away, its rays reach us almost
parallel — which is why the lit part is very nearly an exact half.

Page 7 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Tip: keep the torch at least about 1.5 m away. If you bring it too close, the beam
spreads over less than half the globe and the day–night boundary is no longer
sharp.

Q3 In India, sunrise first occurs in the eastern part and then in other parts. While
looking at the eastern part of India on the globe, rotate the globe in one direction
and then in the opposite direction. What is the direction of rotation when light falls
on the eastern part of India first?

The light falls on the eastern part of India first when the globe is rotated from West to East
about its North–South axis.
Turn the globe the other way (East to West) and you will see the torchlight reach Gujarat before
it reaches Arunachal Pradesh — the opposite of what really happens in India. So that direction
must be wrong.

Why it happens: the place that meets the sunlight first is the one that is carried into
the lit half first. Turning the globe eastward pushes the eastern edge of the dark half
into the light, so eastern India crosses the sunrise line before central and western
India do.

Real-life check: on the same date the Sun rises in Itanagar (Arunachal Pradesh)
roughly two hours before it rises in Dwarka (Gujarat) — yet both places keep the
same clock time, because India uses a single standard time.

Q4 Now while rotating the globe from West to East, observe your location on the Earth.
Does it go through a cycle of day and night?

Yes. The sticker marking your location passes through a complete cycle in every single turn of
the globe.

The sticker crosses from the dark half into the lit half — this is sunrise.
It travels through the lit half — this is daytime, and it is brightest when the sticker faces the
torch squarely (noon).
It crosses back into the dark half — this is sunset.
It travels through the dark half — this is night, and then sunrise comes again.

Page 8 of 43

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Class 7 Science Chapter 12 Earth, Moon, and the Sun
a g l AglaSem · NCERT Solutions

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Why it happens: the Sun's light is always there and always lighting one half of the

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In-text Question — Page 173
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12.1 Rotation of the Earth

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sky during one rotation of the Earth while it rotates from West to East. What will

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12.6?
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Yes — you would observe exactly what the girl in Fig. 12.6 observes. Standing on the
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runs from right to left across the sky.

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Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

TIME OF DAY WHAT YOU SEE (FACING NORTH ON THE EQUATOR)

Morning The Sun appears low down on your right-hand side, in the East.

Around noon You have been carried to a new position; the Sun is now overhead.

Evening You have turned further; the Sun disappears to your left, in the West.

Night You are on the dark half; the stars become visible in the sky.

Why it happens: nothing about the Sun changed during those hours. What changed
is the direction in which you were pointing, because the Earth carried you eastward
through about half a turn. The Sun's apparent journey from East to West is simply
the record of your own journey from West to East.

Tip: stand outdoors facing North (use the Pole Star at night, or a compass). East is
on your right and West on your left — this simple check makes Fig. 12.6 easy to read.

In-text Question — Page 174
12.1 Rotation of the Earth

Q1 Since the Earth is rotating, shouldn't the stars also appear to move in the sky like
the Sun?

Yes, indeed — and they do. The Earth's rotation makes every object in the sky appear to move,
not just the Sun.
Watch the Big Dipper (Saptarishi) on any clear night. Sketch its position at 7 pm and again at 9
pm and 11 pm as in Activity 12.3, and you will find it has swung across the northern sky. Over
the whole night it seems to travel in a big arc around the Pole Star (Dhruva Tara).

Why the Pole Star seems fixed: the Earth's axis of rotation points very close to the
Pole Star. A point straight along the axis does not appear to move as the Earth spins
— so the Pole Star stays almost still while all other stars appear to wheel around it.

Page 10 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Did you know? Astrophotographers keep a camera's shutter open for hours and the
moving stars record themselves as star trails — beautiful arcs of circles all centred
on the Pole Star. That photograph is a direct picture of the Earth's rotation.

Activity 12.3: Let us explore — Page 174
12.1 Rotation of the Earth

ACTIVITY

Q1 After two hours, observe the Big Dipper again. Has it moved? Again, draw its
orientation and note down the time.

Yes, it has clearly moved — and it has also turned, so the whole seven-star pattern is tilted
differently against the same trees or buildings on the ground.
Do the sketching honestly: draw the ground line and a fixed tree or building first, then the seven
stars above it, and write the time beside the sketch. Fig. 12.7 is the record made by a student in
Pune on the night of 1–2 April:

TIME WHERE THE BIG DIPPER IS SEEN

7 pm Low in the Northeast

9 pm Higher, still towards the Northeast

11 pm Highest, nearly due North

1 am Beginning to come down, past North

3 am Lower, towards the Northwest

5 am Low in the Northwest

Why it happens: the Earth turns through 15° every hour (360° ÷ 24 h). In two hours
it turns 30°, so the whole sky appears to slide back by 30°. That is a big, easily visible
shift — about the width of three fists held at arm's length.

Page 11 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Tip: do all the observations from the same spot on the same night, and always
draw the same tree or building. If you change your standing place, the comparison
is spoilt.

Q2 Repeat the above step after two hours. Do you observe that the Big Dipper appears
to move around the Pole Star (notice just the movement even if you cannot see the
Pole Star)?

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.

1 am 11 pm
9 pm
3 am

7 pm
5 am

Northwest Pole Star Northeast

Positions of the Big Dipper through one night, sketched every two hours. All six positions lie on one
circle whose centre is the Pole Star.

Why it happens: the Earth's axis of rotation points almost exactly at the Pole Star. As
the Earth spins, every star appears to swing about that direction — like beads on a
turning wheel swinging about its hub. Stars far from the hub sweep wide arcs; the
Pole Star, sitting at the hub, hardly moves at all.

Page 12 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Check it yourself: the Moon behaves the same way. Like the Sun, it appears to rise
towards the East and set towards the West, because the Earth rotates from West to
East.

In-text Question — Page 175
12.2 Revolution of the Earth

Q1 But, why do different stars appear in the night sky over the course of a year?

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.
At night we are always looking away from the Sun. In March that direction points at one region
of the sky; three months later the Earth has travelled a quarter of the way round its orbit, so at
night we look at a region roughly 90° away.

March

June Sun December

arrows point to
midnight sky
the

September

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Class 7 Science Chapter 12 Earth, Moon, and the Sun
a g l AglaSem · NCERT Solutions

The night side always faces away from the Sun. As the Earth moves round its orbit, that direction
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sweeps through the whole sky in one year — so different stars are seen in different months.

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Why it happens: the Earth takes about 365 days and 6 hours for one revolution.
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and why the book asked you in Grade 6 to look for particular constellations only in
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Try this: look at the same part of the sky at the same clock time on the 1st of two
months in a row. The stars will have shifted by about 30° — a quarter of a right angle
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more than a fist-width, and easy to notice.
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In-text Question — Page 177
12.2.2 Seasons on the Earth
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I have noticed that we go through a cycle of seasons every year. Is it related to the
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revolution of the Earth around the Sun in some way?

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Yes — but the revolution alone is not enough. Seasons happen because of the revolution

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MONTH NORTHERN SUNLIGHT IT RECEIVES SEASON
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December Tilted away from the Sun Less intense, and for less than Winter

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Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Why the tilt matters: because the Earth is a ball, the same bundle of sunrays is
spread over a smaller patch in the hemisphere leaning towards the Sun, so that
patch is heated more; in the other hemisphere the same bundle spreads over a
larger patch and heats it less. The tilt also puts more than half of the leaning
hemisphere in the lit half of the Earth — which is why days are longer in summer
than in winter, exactly as the girl in the picture noticed. More intense sunlight, lasting
longer, adds up to summer.

Key point: the seasons of the Southern Hemisphere are the reverse of ours — June
is winter and December is summer in Australia.

In-text Question — Page 179
12.3 Eclipses

Q1 Day and night cycle, seasons, the life on the Earth... so much is dependent upon the
Sun. Could the light from the Sun get blocked by the two planets which are
revolving between the Earth and the Sun?

No. The two planets that revolve between the Earth and the Sun are Mercury and Venus, and
neither of them can ever block the Sun's light from reaching us.
They are much larger than the Moon, but they are also enormously farther away, so their
apparent size in the sky is tiny compared with the Sun's. When Venus does pass between the
Sun and the Earth it shows up only as a small black dot creeping across the bright face of the
Sun — the rare event called the Transit of Venus.
The Moon, however, can do it. It is far smaller than the Sun in actual size, but it is so much
closer to us that its apparent size in our sky is about the same as the Sun's. That is why the
Moon can cover the Sun completely and cause a solar eclipse.

Why it happens: apparent size depends on actual size and distance. Doubling the
distance halves the apparent size. Venus is roughly 100 times farther from us than
the Moon, so even though it is bigger than the Moon it looks like a dot.

Did you know? A Transit of Venus is rarer than a solar eclipse. The last pair occurred
in 2004 and 2012; the next will not be until 2117.

Page 15 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Activity 12.4: Let us explore — Page 180
12.3.1 Solar eclipse

ACTIVITY

Q1 Now close one eye and show a thumbs up with your outstretched hand towards
your friend as shown in Fig. 12.12. Are you able to cover the entire head of your
friend with your thumb?

your thumb

your friend, about 5 m away

Fig. 12.12, page 180 — trying to cover a friend’s head with the thumb; the friend is
standing about 5 metres away. Redrawn sketch.

Yes — with one eye closed and the arm stretched out, the thumb completely hides the head of a
friend standing about 5 metres away, even though the thumb is far smaller than the head.

OBJECT ACTUAL SIZE DISTANCE FROM YOUR EYE APPARENT SIZE

Your thumb About 2 cm wide About 60 cm Roughly the same as the head's

Friend's head About 16 cm wide About 500 cm (5 m) Roughly the same as the thumb's

Page 16 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

thumb: 2 cm at 60 cm → 2 ÷ 60 ≈ 0.033

head: 16 cm at 500 cm → 16 ÷ 500 ≈ 0.032

The two ratios are nearly equal, so the two apparent sizes are nearly equal.

Why it happens: the size an object seems to have — its apparent size — depends
on its actual physical size and on how far it is from you. A small object held close can
match a large object far away.

This is the whole secret of a solar eclipse: the Sun is about 400 times wider than
the Moon, but it is also about 400 times farther away. So both look almost exactly
the same size in our sky, and the Moon — the "thumb" — can hide the Sun
completely.

Dive Deeper — Pages 171 to 186
Dive Deeper boxes of the chapter

DIVE DEEPER

Q1 Rotation is the motion of an object in which all its parts move in circles around an
imaginary line that passes through it. This line is called the axis of rotation.

This is the exact definition you should learn. Three things are packed into it:

1. All parts move — not just one point. Every particle of the object takes part.
2. Each part moves in a circle — not along a straight line and not randomly.
3. The circles are centred on one imaginary line that passes through the object — the axis
of rotation.

SPINNING ITS AXIS OF ROTATION WHICH PARTS STAY
OBJECT STILL

Spinning top Its spindle The points on the spindle

Ceiling fan The rod through its centre The centre of the hub

Earth The line through the North Pole and the South The two poles
Pole

Page 17 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Rotation is not revolution: in rotation the axis passes through the object itself (the
Earth spinning, once in 24 hours). In revolution the object goes around another
object (the Earth going around the Sun, once in about 365 days and 6 hours).

Q2 Two incorrect reasons often given to explain why seasons occur on the Earth are:
When the Northern Hemisphere tilts towards the Sun, it is closer to the Sun. The
orbit of the Earth is an oval with the Sun slightly displaced from its centre so the
Earth is at different distances from the Sun over the year.

Both of these sound convincing, and both are wrong. The difference in distance is far too small
to matter in either case.

"The tilted hemisphere is nearer." The Earth's radius is only about 6,400 km, while the
Earth–Sun distance is about 150 million km. Tilting brings the Northern Hemisphere nearer
by a few thousand kilometres out of 150 million — a change of well under one-hundredth of
one per cent. It cannot make a season.
"The Earth is nearer to the Sun in some months." The orbit is only very slightly oval. The
Earth's closest and farthest distances are about 147 million km and 152 million km — a
difference of roughly 3%.

Farthest − closest = 152 − 147 = 5 million km

As a fraction of the distance: 5 ÷ 150 ≈ 0.033 = about 3% only.

The decisive fact: the Earth is closest to the Sun in January — the depth of the
Northern Hemisphere's winter, and the height of the Southern Hemisphere's
summer. If distance decided the seasons, both hemispheres would have summer
together in January. They do not. So distance is not the cause; the tilt of the axis
and the spherical shape of the Earth are.

Page 18 of 43

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Class 7 Science Chapter 12 Earth, Moon, and the Sun
a g l AglaSem · NCERT Solutions

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In the Northern Hemisphere, the longest day occurs around 21 June—this is known
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as summer solstice. After the summer solstice, the duration of a day becomes
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Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q4 Though the planets Mercury and Venus are much larger than the Moon in size, they
are also much farther from the Earth as compared to the Moon. Thus, their
apparent sizes are very much smaller than the Sun and they cannot block the Sun.
For example, when Venus passes between the Sun and the Earth, it appears as a
tiny black dot passing against the bright face of the Sun. This event, known as a
Transit of Venus, is a rare event.

The box is really a second application of Activity 12.4 — apparent size decides everything, and
apparent size depends on both actual size and distance.

BODY ACTUAL DIAMETER DISTANCE FROM APPARENT SIZE IN OUR
THE EARTH SKY

Moon About 3,500 km — smallest About 3.8 lakh km — About the same as the Sun's — it
of the three nearest can cover the Sun

Venus About 12,000 km — bigger Tens of millions of km A tiny dot
than the Moon — far away

Mercury About 4,900 km — bigger Even farther than Venus A tinier dot
than the Moon at transit

Why it happens: being big is not enough. The Moon wins the contest only because
it is so close. A transit of Venus therefore never darkens the day; it just puts a black
speck on the Sun's disc, which can be seen only with proper, safe solar projection —
never by looking at the Sun.

Did you know? Transits of Venus come in pairs eight years apart, and then not again
for more than a century. The last pair was in 2004 and 2012.

Page 20 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q5 This activity, similar to Activity 11.5, is to be set up by your teacher. A mirror can be
used to project an image of the Sun onto a wall. However, holding it at the correct
angle throughout a solar eclipse can be difficult. To solve this, make a movable
stand for the mirror. Use a hollow ball with a small hole, half-fill it with sand (to
keep it stable), and attach a small mirror (such as an embroidery mirror) to it. Place
the ball on a circular ring, like an adhesive tape ring, so it can be turned around
easily. Adjust it until the Sun's image appears on a wall or screen. Fig. 12.15 shows
this set-up where the mirror is fixed to a green ball.

Screen with the Sun's image

Ball with mirror

Fig. 12.15, page 181 — a public solar eclipse viewing organised in Ooty, Tamil Nadu, with
the mirror fixed to a green ball and the Sun’s image thrown on a screen. Redrawn
sketch; see the textbook for the photograph.

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.

1. Take a hollow ball with a small hole and half-fill it with dry sand. The sand lowers the centre
of gravity so the ball sits steadily instead of rolling away.
2. Stick a small mirror — an embroidery mirror is ideal — on the outside of the ball.
3. Rest the ball on a ring, for example a roll of adhesive tape. The ball can now be nudged in
any direction and it stays where you leave it, so it works as a movable stand.
4. Turn the ball until the patch of reflected sunlight lands on a wall or a white screen in the
shade. Move the screen farther away to get a bigger but dimmer image, nearer for a
smaller but brighter one.

Page 21 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

5. During the eclipse, the round patch on the wall is a real image of the Sun. Watch the Moon's
dark bite grow and shrink on the wall.

Why a small mirror works: a small flat mirror far from the screen behaves like a
pinhole — the bright patch stops being a square copy of the mirror and becomes a
round image of the Sun itself. That is why the shape of the patch changes during the
eclipse.

Caution: this activity must be done strictly under the supervision of a teacher.
Never direct the reflected beam into anyone's eyes, and never look at the Sun or at
the mirror itself.

Q6 In reality, the planets move around a special point in the solar system, which is very
close to the Sun but not exactly at its centre! The Sun also moves around the same
point a little instead of staying perfectly still. Scientists use such tiny wobbles in the
movement of other stars to discover exoplanets around them!

The picture of a fixed Sun with planets going round it is a very good approximation, but not the
whole truth.
The Sun and its planets pull on each other. So the Sun and a planet both go around a common
balance point that lies between them — extremely close to the Sun's centre, because the Sun is
so much more massive, but not exactly at it. The Sun therefore traces a tiny loop of its own
instead of standing perfectly still.

Why this is so useful: other stars must wobble in the same way if they have planets.
Those planets are far too faint to photograph, but the star is bright — and a careful
measurement of its small, regular wobble reveals a hidden planet. Planets found
around other stars in this way are called exoplanets.

Everyday model: hold hands with a friend of about your own weight and spin.
Neither of you stands still — you both circle a point midway between you. Now let a
much heavier adult spin a small child in the same way: the adult barely shifts, but
does shift a little. That small shift is the Sun's wobble.

Science and Society — Page 183

Page 22 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

12.3.2 Lunar eclipse

SCIENCE AND SOCIETY

Q1 Using the computer version of Stellarium app, which is free, you may get
information about the upcoming solar and lunar eclipses (if any) which may be
visible from your location.

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.

1. Install the desktop version of Stellarium and open it.
2. Set your location — type the name of your town, or enter its latitude and longitude.
3. Set the date and time you want to check.
4. Use the sky-and-viewing options to find the Sun or the Moon and run the clock forward.
During a solar eclipse you will see the Moon's disc slide over the Sun; during a lunar eclipse
you will see the Earth's shadow cross the Moon.
5. Note down the date, the starting time, the greatest phase and whether it is total or partial
for your location.

Why it is worth doing as a class: an eclipse visible from India may be only partial
where you live and not visible at all a thousand kilometres away. Checking it in
advance lets your school plan a proper, safe viewing session with eclipse goggles or
a mirror projection.

The science behind it: the program is simply calculating the positions of the Sun,
the Earth and the Moon. Indian astronomers did the same thing centuries ago, by
hand — the Surya Siddhanta gives rules for predicting eclipses, written as rhythmic
Sanskrit shlokas.

Know a Scientist — Page 184

Page 23 of 43

as e
Class 7 Science Chapter 12 Earth, Moon, and the Sun
a g l AglaSem · NCERT Solutions

Know a Scientist: M.K. Vainu Bappu
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KNOW A SCIENTIST

.co a g l
a s emVainu Bappu is known as the father of modern Indian astronomy. He led
gl
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efforts in setting up many instruments and telescopes in India, such as the
telescopes at Manora Peak near Nainital (Uttarakhand) and Kavalur (Tamil Nadu).

. com
The observatory at Kavalur has been named after him. He mainly studied stars and
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even discovered a comet. He alsoetravelled
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M.K. Vainu Bappu (1927–1982) is called the father of modern Indian astronomy

. co on which Indian astronomy still stands.
built the facilities
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aglWHAT HE DID WHY IT MATTERED

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em
near Nainital (Uttarakhand)

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Led the setting up of the observatory at Kavalur Home to a large optical telescope; the observatory now carries
his name

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distances

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agl Travelled the world to observe solar eclipses A total solar eclipse lasts only a few minutes and is visible from a
narrow strip, so astronomers must go to it
se m
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Why astronomers chase eclipses: for those few minutes the blinding disc of the
Sun is hidden, and the faint outer atmosphere of the Sun becomes visible. As the
chapter says, an eclipse gives an opportunity to study things that cannot be
co m
observed otherwise.
m .
m as e
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s e m Did you know? The Vainu Bappu Observatory at Kavalur is run by the Indian
agla Institute of Astrophysics (IIA), Bengaluru — the same institute that runs the
.c
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Kodaikanal Solar Observatory, set up in 1899.

m a s e
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Let Us Enhance OuraLearning — Pages 184 to 186

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Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Chapter exercises

LET US ENHANCE OUR LEARNING

Q1 In Fig. 12.17, how many hours of sunlight do the North Pole and the South Pole
receive during one rotation of the Earth?

NP

SP

Fig. 12.17, page 184 — the Earth with one half of it lit. The tilted axis of rotation is
dashed and the two poles are marked NP and SP.

Read the picture carefully. Sunlight is falling from the left, so the left half of the globe is lit and
the right half is dark. The axis is tilted, and the two poles are marked on it:

The NP dot lies on the dark side of the day–night boundary.
The SP dot lies on the lit side of it.

Page 25 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

A pole sits on the axis, so it does not cross the boundary at all while the Earth spins — it simply
stays where it is for the whole rotation.

North Pole: sunlight for 0 hours (dark for all 24 hours)

South Pole: sunlight for 24 hours (no night at all)

Sunrays
NP — in the dark half
0 hours of sunlight

Day Night

SP — in the lit half: 24 hours of
sunlight

In Fig. 12.17 the North Pole lies in the dark half and the South Pole in the lit half. Because the poles lie
on the axis, they stay there through the whole rotation.

Which month is this? The North Pole is turned away from the Sun, so the figure
shows the December situation — compare it with Fig. 12.11(b), where the caption
reads "The North Pole is in darkness for all 24 hours in December". In June the
picture would be exactly reversed: 24 hours of sunlight at the North Pole and none
at the South Pole.

Page 26 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q2 Fill in the blanks: (i) Stars rise in the _________ and set in the ___________. (ii) Day and
night are caused by the Earth's __________________. (iii) When the Moon fully covers the
Sun from our view, it is called a _____________ solar eclipse.

NO. COMPLETED SENTENCE

(i) Stars rise in the East and set in the West.

(ii) Day and night are caused by the Earth's rotation (on its own axis).

(iii) When the Moon fully covers the Sun from our view, it is called a total solar eclipse.

Why these answers:

(i) The Earth rotates from West to East, so every object in the sky — the Sun, the
Moon and the stars alike — appears to travel the other way, rising in the East and
setting in the West.
(ii) Rotation, not revolution. One rotation takes about 24 hours and gives exactly
one day and one night. Revolution takes a year and gives the seasons.
(iii) If only a part of the Sun is covered, it is a partial solar eclipse; when the
Moon's disc covers the whole of the Sun, it is total.

Page 27 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q3 State whether True or False: (i) Lunar eclipse occurs when the Sun comes between
the Earth and the Moon. (ii) Sunrise happens earlier in Gujarat than in Jharkhand.
(iii) In Chennai, the longest day occurs on the summer solstice. (iv) We should watch
the solar eclipse directly with our naked eye. (v) Seasons occur due to the tilt of
Earth's axis of rotation and its spherical shape. (vi) The Earth's revolution around
the Sun causes day and night.

NO. STATEMENT TRUE / REASON
FALSE

(i) Lunar eclipse occurs when False A lunar eclipse occurs when the Earth comes
the Sun comes between between the Sun and the Moon, so the Earth's
the Earth and the Moon shadow falls on the Moon.

(ii) Sunrise happens earlier in False The Earth turns West to East, so eastern places see
Gujarat than in Jharkhand the Sun first. Jharkhand is east of Gujarat, so
sunrise there is earlier — by roughly half an hour.

(iii) In Chennai, the longest True Chennai is in the Northern Hemisphere, so its
day occurs on the summer longest day is the summer solstice, around 21 June.
solstice (Being near the equator, the day is only a little
longer than 12 hours.)

(iv) We should watch the solar False Even during an eclipse the Sun is intense enough to
eclipse directly with our damage the eyes and cause blindness. Direct
naked eye viewing must be strictly avoided — and sunglasses,
binoculars and telescopes are not safe either.

(v) Seasons occur due to the True This is exactly the reason given in the chapter.
tilt of Earth's axis of Distance from the Sun is not the reason.
rotation and its spherical
shape

(vi) The Earth's revolution False Day and night are caused by the Earth's rotation
around the Sun causes day on its own axis. Revolution causes the year, and
and night with the tilt, the seasons.

Tip: in statements (i) and (vi) only one word has been swapped. Read such sentences
slowly and ask, "which body is in the middle?" and "spinning or going around?"

Page 28 of 43

ase
Class 7 Science Chapter 12 Earth, Moon, and the Sun
a g l AglaSem · NCERT Solutions

co m
m.
Padmashree saw the Orion constellation nearly overhead at 8 pm yesterday. When
e
Q4

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will she see Orion overhead today?

a g
se m
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She will see Orion overhead about four minutes earlier — at roughly 7:56 pm today.

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Earth's revolution: 360° in about 365 daysm
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The Earth turns 15° in one hour, so 1° takes 60 ÷ 15 = 4 minutes
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Time today = 8:00 pm − 4 minutes = about 7:56 pm
m l
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a s emit happens: the Earth does not only spin — it also moves along its orbit by
a gl Why
about one degree each day. A star returns to the same place in the sky after one

m so the stars gain about four minutes on a s
coSun, agl
rotation (about 23 hours 56 minutes), but the Sun needs about 24 hours because of
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that extra degree. Our clocks follow the
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the clock every day.

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Check it yourself: four minutes a day adds up to about two hours in a month, and
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A full 24-hour shift brings the stars back to the same clock time on the same date.
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Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Why it happens: a group of stars rises at midnight only when the Earth is at a
particular point in its orbit — the point from which the midnight sky faces that part
of space. The Earth returns to that point after one complete revolution, which takes
about 365 days and 6 hours. So the same star group rises at midnight once every
year.

Tip: in between, the group rises about four minutes earlier each night — around 10
pm two months later, and around 8 pm four months later.

Q6 Abhay noticed that when it was daytime in India, his uncle who was in the USA was
generally sleeping as it was night-time there. What is the reason behind this
difference?

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.

AT THAT INSTANT INDIA USA

Position on the globe In the half facing the Sun In the half turned away from the Sun

What people experience Daytime — school, work Night — sleeping

Why it happens: as the Earth rotates from West to East, each place is carried in turn
into the lit half and then out of it. India is far to the east of the USA, so India meets
the sunlight roughly half a day earlier. Twelve hours later the positions are
exchanged: it is night in India and day in the USA.

Everyday proof: when a cricket match starts at 5 am in India for a tour of the USA or
Australia, it is because the match is being played in daylight there while it is still dark
here. Time zones exist for exactly this reason.

Page 30 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q7 Four friends used the following ways to see the solar eclipse. Who among them was
being careless? (i) Ravikiran used a solar eclipse goggle. (ii) Jyothi used a mirror to
project the Sun's image. (iii) Adithya saw the Sun directly with his eyes. (iv) Aruna
attended a programme arranged by a planetarium.

Adithya — option (iii) — was being careless.

FRIEND METHOD SAFE? WHY

Ravikiran Solar eclipse goggle Safe Special filters made for solar viewing cut
down the Sun's light and harmful radiation
to a safe level.

Jyothi Mirror projecting the Safe She looks at an image on a screen, never at
Sun's image the Sun. This is the set-up of Fig. 12.15.

Adithya Looked directly with Dangerous Even during an eclipse the Sun is intense
his eyes enough to damage the eyes and cause
blindness.

Aruna Programme arranged Safe — and the The organisers provide specialised eye
by a planetarium best choice protection and also explain the science.

Why direct viewing is so dangerous: the eye has no pain sensors in its light-
sensitive layer, so the damage is done silently and may be noticed only hours later —
and it can be permanent. Sunglasses, smoked glass, exposed film, binoculars and
telescopes are not safe substitutes; binoculars and telescopes actually make it worse
by concentrating the light.

Page 31 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q8 Fill in the circles in Fig. 12.18 appropriately with one of the following: Sun, Moon,
Earth.

Solar eclipse

Sun

Lunar eclipse

Moon

Fig. 12.18, page 185 — the circles to be filled in.

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

ROW OF FIG. 12.18 FIRST CIRCLE MIDDLE CIRCLE LAST CIRCLE

Solar eclipse Sun (given) Moon Earth

Lunar eclipse Sun Earth Moon (given)

Page 32 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Solar eclipse
Moon

Sun Earth

Moon's shadow falls on the Earth

Lunar eclipse
Moon

Sun Earth

Earth's shadow falls on the
Moon

Solar eclipse: Sun – Moon – Earth. Lunar eclipse: Sun – Earth – Moon. In each case the middle body
casts the shadow.

Why this order: in a solar eclipse it is the Sun that is hidden from us, so the Moon
must stand between the Sun and us. In a lunar eclipse it is the Moon that goes dark,
so the Earth must stand between the Sun and the Moon and block the sunlight that
would have lit the Moon.

Q9 The Moon is much smaller than the Sun, yet it can block the Sun completely from
our view during a total solar eclipse. Why is it possible?

Because what matters for covering something is not the actual size but the apparent size — the
size an object seems to have when seen by our eye. Apparent size depends on the actual size
and on the distance.
The Moon is far smaller than the Sun, but it is also enormously closer to us. The two effects
cancel almost exactly, so the Moon and the Sun look nearly the same size in our sky. That is
why the Moon's disc can just cover the Sun's disc completely.

Sun: about 400 times wider than the Moon

Sun: about 400 times farther from us than the Moon

Apparent size ∝ size ÷ distance → the two ratios come out nearly equal

Page 33 of 43

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Class 7 Science Chapter 12 Earth, Moon, and the Sun
a g l AglaSem · NCERT Solutions

co m
m.
Activity 12.4 is the proof: your thumb is only about 2 cm wide and your friend's

m l a se
head about 16 cm, yet the thumb hides the head completely from 5 metres away —
o
m .c thumb is only about 60 cm from your eye. The Moonagis doing exactly
because the
a e thumb does.
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what

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Did you know? Mercury and Venus are much bigger than the Moon but far more
.
mWhen Venus passes in front of the Sun it
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distant, so their apparent sizes are tiny.
a as an eclipse.
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appears only as a black dot — never

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The Indian cricket team matches in Australia are often held in December. Should
co pack winter or summer clothes for their trip? gl
Q10

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They should pack summer clothes. December is summer in Australia, even though it is winter
a s
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IN DECEMBER
a gl
INDIA (NORTHERN AUSTRALIA (SOUTHERN
HEMISPHERE) HEMISPHERE)

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Tilt of that Tilted away from the Sun Tilted towards the Sun

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hemisphere

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Sunlight Less intense, less than 12 hours a day More intense, more than 12 hours a day

ag
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Season Winter Summer

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Why it happens: the Earth keeps its axis tilted in the same direction all year. In

a gl
December the Southern Hemisphere leans towards the Sun, so Australia gets more
intense sunlight for longer — summer. Six months later, in June, the situation is
exactly reversed.
co m
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ag starts on 26 December, in
.cCricket check: the famous Boxing Day Test at Melbourne
m the middle of the Australian summer — light cotton clothes, sunscreen and a hat,
l a se
ag
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not woollens.

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Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q11 Why do you think lunar eclipses can be seen from a large part of the Earth when
they happen, but total solar eclipse can be seen by only a small part of the Earth?

Because of the size of the shadow in each case, and because of who has to be inside the
shadow.

Solar eclipse. The small Moon casts a narrow shadow, and the tip of its dark shadow makes
only a small spot on the Earth's surface. Only observers standing inside that spot see the
total eclipse. Around that spot, where the Sun is only partly blocked, people see a partial
eclipse.
Lunar eclipse. The much larger Earth casts a broad shadow, and the whole Moon fits inside
it. The eclipsed Moon is then dark for everyone on the night side of the Earth — that is, for
nearly half the planet at once.

Solar eclipse — small shadow spot on a big Earth
Moon

Earth

only this small spot sees totality

Lunar eclipse — small Moon inside a big shadow
Moon

Earth

everyone on the night side can
watch

A small body casting a shadow on a large one gives a small patch of totality; a large body casting a
shadow on a small one swallows it whole.

One more reason for the "few minutes": because of the Earth's rotation and the
Moon's motion in its orbit, the Moon's shadow keeps sweeping across the Earth's
surface. So even in the lucky spot, totality lasts only a few minutes — while a total
lunar eclipse can go on for an hour or more, since the Moon takes that long to cross
the Earth's wide shadow.

Page 35 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Q12 If the Earth's axis were not tilted with respect to the axis of revolution, explain
what would be the effect on seasons?

There would be no seasons at all. Every place on the Earth would have the same kind of
weather throughout the year, and every day would be like an equinox day.
With an upright axis, the day–night boundary would always pass exactly through both poles. So:

Day and night would be 12 hours each, everywhere, on every day of the year. There
would be no long summer days and no short winter days.
Neither hemisphere would ever lean towards the Sun, so the intensity of sunlight at any
place would stay the same all year.
Places near the equator would be permanently hot, the middle latitudes permanently mild
and the polar regions permanently cold — but none of them would ever change.
There would be no summer solstice, no winter solstice, no six-month polar day and no six-
month polar night.

Why the tilt is the cause: the tilt does two things at once. It makes the sunrays fall
more steeply on the hemisphere leaning towards the Sun, so the same bundle of
light is concentrated on a smaller area, and it keeps more than half of that
hemisphere inside the lit half, so the daytime is longer. Remove the tilt and both
effects vanish together — and the seasons vanish with them.

Common trap: the Earth would still revolve around the Sun and would still be a little
nearer in January. That would not bring back the seasons, because the change in
distance is far too small — the same reason given in the Dive Deeper box on page
178.

Exploratory Projects — Page 186

Page 36 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Interdisciplinary projects

EXPLORATORY PROJECTS

Q1 Repeat Activity 12.2 but replace the torch with an electric lamp. Then place the
globe at different positions on a circle around the lamp while maintaining the tilt of
the globe. (i) Note down your observations regarding how much of the Northern
and Southern hemispheres of the globe are illuminated at different positions. (ii)
Rotate the globe and take a note of the length of the day and night on different
parts of the globe. (iii) Repeat (ii) for different positions of globe on the circle.

This project turns the whole chapter into one table-top model. The one rule that must never be
broken: the globe's axis must keep pointing in the same direction — the same way, towards the
same corner of the room — at every position on the circle. Do not turn the stand to face the
lamp.
How to set it up

1. Stand a bare electric lamp (no shade) in the middle of a table in a dark room. This is the Sun.
2. Chalk a circle of radius about 60–75 cm around the lamp. Mark four positions on it: June,
September, December, March.
3. Carry the globe around the circle, keeping the axis tilted the same way throughout, and stop
at each mark.

(i) How much of each hemisphere is lit

POSITION NORTHERN SOUTHERN POLES
HEMISPHERE HEMISPHERE

June More than half of it is lit Less than half of it is lit North Pole fully lit; South Pole
fully dark

September Exactly half Exactly half The lit–dark line passes
through both poles

December Less than half of it is lit More than half of it is lit North Pole fully dark; South
Pole fully lit

March Exactly half Exactly half The lit–dark line passes
through both poles

(ii) and (iii) Length of day and night — at each position, spin the globe slowly and watch a
sticker on Delhi, one on the equator and one on Australia. Count roughly what fraction of each
turn the sticker spends in the light.

Page 37 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

PLACE ON THE GLOBE JUNE POSITION MARCH / DECEMBER
SEPTEMBER POSITION

Delhi (Northern Hemisphere) Day longer than Day ≈ night Day shorter than night
night

On the equator Day ≈ night Day ≈ night Day ≈ night

Australia (Southern Day shorter than Day ≈ night Day longer than night
Hemisphere) night

North Pole 24 hours of day On the boundary 24 hours of night

What the model proves: the lamp never changed and the distance never changed
— only the direction of the tilt with respect to the lamp changed. That alone
produced longer days, shorter days and midnight sun. This is the strongest possible
demonstration that the seasons come from the tilt, not from the distance.

Tip: use a lamp without a shade so light spreads in all directions, and keep the room
really dark. Take a photograph of the globe at each position — the four pictures side
by side make an excellent chart for the class.

Q2 The Earth goes around the Sun in an oval-shaped path. Draw two circles with the
same centre, one with a radius of 14.7 cm, and another one with a radius of 15.2 cm.
If 1 cm corresponds to 10 million km, the two circles represent the closest and
farthest distances from the Sun. Note how small is the difference between these
two distances.

Do the drawing on a full A4 sheet with a compass, marking the same centre for both circles.

Scale: 1 cm = 10 million km

Closest distance = 14.7 cm × 10 = 147 million km

Farthest distance = 15.2 cm × 10 = 152 million km

Difference on paper = 15.2 − 14.7 = 0.5 cm (5 mm)

Difference in reality = 152 − 147 = 5 million km

As a fraction = 0.5 ÷ 15.2 ≈ 0.033 = about 3%

Page 38 of 43

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Class 7 Science Chapter 12 Earth, Moon, and the Sun
a g l AglaSem · NCERT Solutions

What you will see: the two circles are so close together that from a step away they look like one
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thick line. Yet that 5 mm gap stands for five million kilometres.
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What the drawing proves: the Earth's orbit is very nearly a circle. Textbook pictures
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thinking that seasons come from the changing distance. A 3% change in distance

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cannot produce summer and winter — the tilt of the axis does that.

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Add this to your poster: the a g is at its closest to the Sun in January — the
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coldest month in North India. Write that under the two circles; it settles the

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argument at once.

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a glQ3 Suppose the tilt of the Earth's axis of rotation increases. Will it cause more extreme
seasons? Find out if the tilt of Uranus is more than the Earth and about the seasons

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there. Write an interesting article for a newspaper or your school magazine about
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ANSWER a g
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Yes — a bigger tilt would make the seasons far more extreme, and Uranus is the spectacular

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EARTH URANUS

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Time for one About 1 year About 84 Earth years

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revolution

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Length of one season About 3 months About 21 Earth years

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At the poles Six months of day, six months of About 42 years of continuous day, then about 42
night years of night
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Sample article — you can adapt this in your own words:
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a g l Page 39 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Sample answer:
The Planet That Lies Down
On the Earth, a season lasts about three months, and we grumble when June is too
hot or January too cold. Blame the tilt: our planet's axis leans by about 23.5°, so each
hemisphere takes its turn to face the Sun.
Now imagine tipping that axis right over. That is Uranus. Its axis is tilted by about
98°, which means it does not spin like a top at all — it rolls around the Sun like a ball.
For part of its orbit its north pole points almost straight at the Sun; half an orbit later
its south pole does.
Uranus needs about 84 Earth years for one trip around the Sun, so each of its
seasons drags on for roughly 21 years. At its poles the Sun does not set for about 42
years — and then does not rise for the next 42. A person born at the Uranian north
pole would be middle-aged before seeing a single sunrise.
The lesson for us is simple. Seasons are not about how near a planet is to the Sun;
they are about how it leans. Tilt a planet a little and you get spring and autumn. Tilt
it right over and you get a world of endless summers and endless nights.

Why a bigger tilt means harsher seasons: a larger tilt makes the summer Sun
climb higher (so its rays are concentrated on a still smaller area) and makes the
summer day still longer, while the winter Sun stays lower for a still shorter day. Both
effects grow together, so summers become hotter and winters colder.

Chapter at a glance
The Earth rotates on its own axis — an imaginary line through the geographic North Pole
and South Pole — once in about 24 hours. Seen from above the North Pole, this rotation is
anti-clockwise, that is, from West to East.
Because we watch the sky from a rotating Earth, the Sun, the Moon and the stars only
appear to move. They seem to rise in the East and set in the West. This is exactly like the
trees appearing to turn the other way when you ride a merry-go-round.
The Earth's rotation causes the day–night cycle: the half facing the Sun has day, the other
half has night. The Earth's axis points very close to the Pole Star (Dhruva Tara), so that star
appears almost fixed while all other stars, such as the Big Dipper (Saptarishi), appear to
swing around it.
The Earth also revolves around the Sun along a nearly circular orbit, completing one
revolution in about 365 days and 6 hours. Because of this, the stars seen just after sunset
change gradually through the year.

Page 40 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Seasons occur because the Earth's axis of rotation is tilted with respect to its orbit and
because the Earth is spherical — not because the Earth comes closer to the Sun. (In fact the
Earth is closest to the Sun in January.) The tilted, spherical Earth gives one hemisphere
more intense sunlight for more hours — that hemisphere has summer.
In the Northern Hemisphere the longest day is around 21 June (summer solstice) and the
shortest around 22 December (winter solstice); day and night are equal near 21 March and
23 September (spring and autumn equinox). The Southern Hemisphere has the opposite
seasons.
A solar eclipse happens when the Moon comes between the Sun and the Earth and its
shadow falls on the Earth. It is total in a small region and partial around it. Never look at
the Sun directly during an eclipse — not even through sunglasses, binoculars or a
telescope.
A lunar eclipse happens when the Earth comes between the Sun and the Moon and the
Earth's shadow falls on the Moon. In a total lunar eclipse the Moon looks dark red. A lunar
eclipse is completely safe to watch with the naked eye.

Page 41 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

Quick revision

TERM WHAT IT MEANS EXAMPLE / DETAIL FROM POINT TO REMEMBER
THE CHAPTER

Rotation The motion of an object in A spinning top, a ceiling fan, a The imaginary line is called
which all its parts move in ball spun on a finger — and the axis of rotation
circles around an imaginary line the Earth, once in about 24
passing through it hours

Earth's axis The line through the geographic Viewed from above the North It is tilted with respect to
of rotation North Pole and the South Pole Pole the Earth turns anti- the orbit, and it points very
about which the Earth spins clockwise, West to East close to the Pole Star

Revolution The motion of an object around The Earth around the Sun in Rotation is spinning on its
another object about 365 days and 6 hours; own axis; revolution is
the Moon around the Earth going around something
else

Orbit The path an object takes while Seen from the top, the Earth's It looks elongated in books
revolving around another object orbit around the Sun is nearly only because that picture is
circular a side view

Day and The lit half of the Earth has day, Sunrise as your place turns Caused by rotation — not
night the dark half has night into the light, sunset as it by revolution
turns into the dark (Fig. 12.5)

Pole Star The star lying almost exactly The Big Dipper (Saptarishi) It appears nearly stationary
(Dhruva along the Earth's axis in the appears to circle around it because the axis points at
Tara) Northern Hemisphere through the night (Fig. 12.7) it

Seasons The yearly cycle of summer, June: Northern Hemisphere Caused by the tilt of the
winter and the rest tilted towards the Sun — axis plus the spherical
summer; December — winter shape of the Earth

Solstice The day with the longest or the About 21 June (summer On 21 June the North Pole
shortest daytime solstice) and 22 December gets sunlight for all 24
(winter solstice) in the hours
Northern Hemisphere

Equinox A day on which daytime lasts Around 21 March (spring) and The equator has nearly 12
about 12 hours everywhere 23 September (autumn) in the hours of daylight on every
Northern Hemisphere day of the year

Apparent The size of an object as seen by A thumb can cover a friend's It depends on the actual
size the eye head 5 m away (Activity 12.4) size and the distance from
the observer

Page 42 of 43

Class 7 Science Chapter 12 Earth, Moon, and the Sun AglaSem · NCERT Solutions

TERM WHAT IT MEANS EXAMPLE / DETAIL FROM POINT TO REMEMBER
THE CHAPTER

Solar eclipse The Moon comes between the Total in the small dark region, Never view it directly — use
Sun and the Earth and blocks partial around it (Fig. 12.13) only a projected image or
sunlight from reaching us approved eclipse goggles

Lunar eclipse The Earth comes between the Total lunar eclipse — the Perfectly safe to watch with
Sun and the Moon so the Moon turns dark red (Fig. the naked eye
Earth's shadow falls on the 12.16)
Moon

Page 43 of 43