Earth, Moon, and the Sun — Class 7 Science
Curiosity · Chapter 12
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7- Mathematics
- Science
- + 3 more
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
2- Mathematics
- Social Science
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
Chapter summary
Key ideas & terms
- Rotation
- The spinning of the Earth on its own axis, completing one turn in about 24 hours and causing day and night.
- Axis of rotation
- The imaginary line passing through the Earth's North and South Poles about which it rotates; it is tilted, not upright.
- Revolution
- The motion of the Earth around the Sun along its orbit, completing one revolution in about 365 days and 6 hours.
- Tilt of the axis
- The slanting of the Earth's axis with respect to its orbit, which, together with the Earth's spherical shape, causes the seasons.
- Solar eclipse
- The event when the Moon comes between the Sun and the Earth and blocks the Sun's light from reaching the Earth.
- Lunar eclipse
- The event when the Earth comes between the Sun and the Moon, casting its shadow on the Moon.
Extra questions & answers
What is the rotation of the Earth and how long does it take?
Rotation is the spinning of the Earth on its own axis; it completes one rotation in about 24 hours.
In which direction does the Earth rotate when viewed from above the North Pole?
Viewed from above the North Pole, the Earth rotates in the anti-clockwise direction, that is, from West to East.
Why does the Sun appear to rise in the East and set in the West?
Because the Earth rotates from West to East, the Sun only appears to move across the sky from East to West; it is the Earth that is actually turning.
What causes the day-night cycle?
The Earth's rotation from West to East causes day and night; the side facing the Sun has daytime while the other side is dark and has night.
Why does the Pole Star appear nearly stationary?
The Earth's axis of rotation points very close to the Pole Star, so it appears almost fixed while all other stars seem to move around it.
What is the revolution of the Earth and how long does it take?
Revolution is the motion of the Earth around the Sun along its orbit; it completes one revolution in about 365 days and 6 hours.
What actually causes the seasons on the Earth?
The seasons are caused by the tilt of the Earth's axis of rotation and the spherical shape of the Earth, not by the changing distance from the Sun.
How can the small Moon block the much larger Sun during a solar eclipse?
Although the Moon is much smaller than the Sun, it is much closer to us, so its apparent size is similar to the Sun's and it can cover the Sun.
When does a lunar eclipse occur?
A lunar eclipse occurs when the Earth comes between the Sun and the Moon, so the Earth's shadow falls on the full disc of the Moon.
Which eclipse can be safely watched with the naked eye, and which cannot?
A lunar eclipse can be safely watched with the naked eye, but a solar eclipse must never be viewed directly as it can damage the eyes.
Let Us Enhance Our Learning
1. 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 shows the June position when the Northern Hemisphere is tilted towards the Sun. During one complete rotation of the Earth in about 24 hours, the North Pole remains in sunlight for the whole rotation, so it receives about
2. Fill in the blanks (i) Stars rise in the _________ and set in the ___________.
Stars rise in the East and set in the West. This apparent motion from East to West is because the Earth rotates from West to East when seen from above the North Pole.
2. Fill in the blanks (ii) Day and night are caused by the Earth’s __________________.
Day and night are caused by the Earth’s rotation on its own axis from West to East, which takes about
2. Fill in the blanks (iii) When the Moon fully covers the Sun from our view, it is called a _____________ solar eclipse.
When the Moon fully covers the Sun from our view, it is called a total solar eclipse. The Moon’s shadow then falls on a small area of the Earth and that area becomes dark for a few minutes.
3. State whether True or False (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 and the Earth’s shadow falls on the Moon. When the Sun comes between the Earth and the Moon a solar eclipse occurs.
3. State whether True or False (ii) Sunrise happens earlier in Gujarat than in Jharkhand.
False. The Earth rotates from West to East, so eastern places see the Sun first. Jharkhand is to the east of Gujarat, so sunrise occurs earlier in Jharkhand than in Gujarat.
3. State whether True or False (iii) In Chennai, the longest day occurs on the summer solstice.
True. Chennai is in the Northern Hemisphere. For the Northern Hemisphere the longest day and shortest night occur around
3. State whether True or False (iv) We should watch the solar eclipse directly with our naked eye.
False. Even during an eclipse the Sun’s light is intense enough to damage the eyes and cause blindness. A solar eclipse must never be viewed directly with the naked eye, sunglasses, binoculars or telescope. Safe methods are certified solar eclipse goggles or projection methods or attending an organised viewing.
3. State whether True or False (v) Seasons occur due to the tilt of Earth’s axis of rotation and its spherical shape.
True. The Earth’s axis is tilted with respect to its orbit and the Earth is spherical. This causes the intensity of sunlight and the length of day to change through the year, giving rise to seasons. Distance from the Sun is not the main cause.
3. State whether True or False (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 axis. Revolution of the Earth around the Sun in about
4. Padmashree saw the Orion constellation nearly overhead at 8 pm yesterday. When will she see Orion overhead today?
Stars appear to rise and set about
5. 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?
She will see the same group of stars rising at midnight again around
6. 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?
The Earth is spherical and only half of it is illuminated by the Sun at a time. Because the Earth rotates from West to East, different longitudes face the Sun at different times. When India, on the eastern side, faces the Sun and has day, the USA, which is far to the west, is on the dark side and has night. This is why we have time zones.
7. Four friends used the following ways to see the solar eclipse. Who among them was being careless? (i) Ravikiran used a solar eclipse goggle.
Ravikiran was not careless. Using a certified solar eclipse goggle made for safe solar viewing is a correct, safe method if the goggle is undamaged and certified.
7. Four friends used the following ways to see the solar eclipse. Who among them was being careless? (ii) Jyothi used a mirror to project the Sun’s image.
Jyothi was not careless. Projecting the Sun’s image with a small mirror onto a wall or screen and looking at the projected image, preferably set up by the teacher and without looking directly at the Sun or reflected beam, is a safe indirect viewing method.
7. Four friends used the following ways to see the solar eclipse. Who among them was being careless? (iii) Adithya saw the Sun directly with his eyes.
Adithya was being careless. Looking directly at the Sun, even during a solar eclipse, with the naked eyes can seriously damage the eyes and cause blindness. This must never be done.
7. Four friends used the following ways to see the solar eclipse. Who among them was being careless? (iv) Aruna attended a programme arranged by a planetarium.
Aruna was not careless. Attending a programme arranged by a planetarium or astronomy club where organisers provide specialised eye protection and guidance is the safest way to watch a solar eclipse.
8. Fill in the circles in Fig. 12.18 appropriately with one of the following: Sun, Moon, Earth.
Solar eclipse: The Moon comes between the Sun and the Earth. So in the three circles for the solar eclipse, the order from the Sun side is Sun at the top, Moon in the middle, Earth at the bottom. Lunar eclipse: The Earth comes between the Sun and the Moon. So for the lunar eclipse, the order is Sun at the top, Earth in the middle, Moon at the bottom.
9. 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?
What we see depends on apparent size, not only physical size. Apparent size depends on both physical size and distance. The Sun is about
10. The Indian cricket team matches in Australia are often held in December. Should they pack winter or summer clothes for their trip?
They should pack summer clothes. Australia is in the Southern Hemisphere, where seasons are opposite to the Northern Hemisphere. When it is winter in India in December, it is summer in Australia with longer days and more intense sunlight, so summer clothing is needed.
11. 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?
During a lunar eclipse the Earth’s large shadow falls on the Moon. Anyone on the night side of the Earth where the Moon is visible can see the same darkened Moon, so more than half the Earth can see it. During a solar eclipse the Moon’s small shadow falls on the Earth and covers only a tiny spot. Due to the small size of the Moon and its shadow, total solar eclipse is visible only along a narrow track where that spot moves, while areas nearby see only a partial eclipse.
12. If the Earth’s axis were not tilted with respect to the axis of revolution, explain what would be the effect on seasons?
If the axis were upright with no tilt, sunlight would fall with almost the same intensity and the day would be about
Exploratory Projects
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.
Keep the globe’s axis tilted in the same direction as you move it around the lamp. At the June position the Northern Hemisphere leans toward the lamp, so more of the Northern Hemisphere is illuminated and less of the Southern Hemisphere. At the opposite December position the Southern Hemisphere leans toward the lamp, so more of the Southern Hemisphere is illuminated. At the March and September positions both hemispheres are equally illuminated, half in light and half in dark.
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. (ii) Rotate the globe and take a note of the length of the day and night on different parts of the globe.
Rotate the globe from West to East. Places near the pole leaning toward the lamp stay in light for more than
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. (iii) Repeat (ii) for different positions of globe on the circle.
When the globe is moved to the opposite side of the lamp, the pattern reverses. In June Northern Hemisphere places have long days and Southern Hemisphere places have long nights; in December the opposite occurs. In March and September both hemispheres have nearly equal day and night everywhere. This demonstrates how revolution with a fixed tilt changes day length and seasons.
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.
Inner radius
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 there. Write an interesting article for a newspaper or your school magazine about it.
Yes, a larger tilt would cause more extreme seasons. A bigger tilt means one hemisphere leans more towards the Sun in its summer, getting more direct, longer-lasting sunlight and hotter summer, and leans more away in winter, getting very slanted sunlight and longer night and colder winter. Uranus is a good example. Its axis is tilted about