NCERT Solutions for Class 7th Science Chapter 12 Chapter exercises — Let Us Enhance Our Learning
Book page 184 to 186 Updated on2026-09-19
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?
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.
Answer
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.
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)
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.
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.
Answer
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.
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.
Answer
No.
Statement
True / False
Reason
(i)
Lunar eclipse occurs when the Sun comes between the Earth and the Moon
False
A lunar eclipse occurs when the Earth comes between the Sun and the Moon, so the Earth's shadow falls on the Moon.
(ii)
Sunrise happens earlier in Gujarat than in Jharkhand
False
The Earth turns West to East, so eastern places see the Sun first. Jharkhand is east of Gujarat, so sunrise there is earlier — by roughly half an hour.
(iii)
In Chennai, the longest day occurs on the summer solstice
True
Chennai is in the Northern Hemisphere, so its longest day is the summer solstice, around 21 June. (Being near the equator, the day is only a little longer than 12 hours.)
(iv)
We should watch the solar eclipse directly with our naked eye
False
Even during an eclipse the Sun is intense enough to damage the eyes and cause blindness. Direct viewing must be strictly avoided — and sunglasses, binoculars and telescopes are not safe either.
(v)
Seasons occur due to the tilt of Earth's axis of rotation and its spherical shape
True
This is exactly the reason given in the chapter. Distance from the Sun is not the reason.
(vi)
The Earth's revolution around the Sun causes day and night
False
Day and night are caused by the Earth's rotation on its own axis. Revolution causes the year, and 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?"
Q4.
Padmashree saw the Orion constellation nearly overhead at 8 pm yesterday. When will she see Orion overhead today?
Answer
She will see Orion overhead about four minutes earlier — at roughly 7:56 pm today.
Earth's revolution: 360° in about 365 days
Extra turn needed each day = 360° ÷ 365 ≈ 1° per day
The Earth turns 15° in one hour, so 1° takes 60 ÷ 15 = 4 minutes
Time today = 8:00 pm − 4 minutes = about 7:56 pm
Why it happens: the Earth does not only spin — it also moves along its orbit by about one degree each day. A star returns to the same place in the sky after one rotation (about 23 hours 56 minutes), but the Sun needs about 24 hours because of that extra degree. Our clocks follow the Sun, so the stars gain about four minutes on the clock every day.
Check it yourself: four minutes a day adds up to about two hours in a month, and to a full 24 hours in a year. That is precisely why Orion is an evening sight in winter and is not seen at all in the June evening sky.
Q5.
Nandhini saw a group of stars rising at midnight on 21 June. When will she see the same group of stars rising at midnight next year?
Answer
She will see the same group rising at midnight again on about 21 June next year — that is, on nearly the same date, one year later.
Gain of the stars on the clock ≈ 4 minutes per day
In one year: 4 min × 365 ≈ 1,460 minutes ≈ 24 hours
A full 24-hour shift brings the stars back to the same clock time on the same date.
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?
Answer
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.
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.
Answer
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 Sun's image
Safe
She looks at an image on a screen, never at the Sun. This is the set-up of Fig. 12.15.
Adithya
Looked directly with his eyes
Dangerous
Even during an eclipse the Sun is intense enough to damage the eyes and cause blindness.
Aruna
Programme arranged by a planetarium
Safe — and the best choice
The organisers provide specialised eye 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.
Q8.
Fill in the circles in Fig. 12.18 appropriately with one of the following: Sun, Moon, Earth.
Fig. 12.18, page 185 — the circles to be filled in.
Answer
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)
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?
Answer
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
Activity 12.4 is the proof: your thumb is only about 2 cm wide and your friend's head about 16 cm, yet the thumb hides the head completely from 5 metres away — because the thumb is only about 60 cm from your eye. The Moon is doing exactly what your thumb does.
Did you know? Mercury and Venus are much bigger than the Moon but far more distant, so their apparent sizes are tiny. When Venus passes in front of the Sun it appears only as a black dot — never as an eclipse.
Q10.
The Indian cricket team matches in Australia are often held in December. Should they pack winter or summer clothes for their trip?
Answer
They should pack summer clothes. December is summer in Australia, even though it is winter in India.
In December
India (Northern Hemisphere)
Australia (Southern Hemisphere)
Tilt of that hemisphere
Tilted away from the Sun
Tilted towards the Sun
Sunlight
Less intense, less than 12 hours a day
More intense, more than 12 hours a day
Season
Winter
Summer
Why it happens: the Earth keeps its axis tilted in the same direction all year. In 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.
Cricket check: the famous Boxing Day Test at Melbourne starts on 26 December, in the middle of the Australian summer — light cotton clothes, sunscreen and a hat, not woollens.
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?
Answer
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.
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.
Q12.
If the Earth's axis were not tilted with respect to the axis of revolution, explain what would be the effect on seasons?
Answer
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.