SCIENCE CLASS- 7
CHAPTER-12 (Earth, Moon, and the Sun)
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?
Image Source- NCERT
Answer:
The North Pole receives 24 hours of sunlight during one rotation of the Earth.
The South Pole receives 0 hours of sunlight (24 hours of darkness).
2. Fill in the blanks.
(i) Stars rise in the _________ and set in the ___________.
Answer: Stars rise in the East and set in the West.
(ii) Day and night are caused by the Earth's __________________.
Answer: Day and night are caused by the Earth's rotation.
(iii) When the Moon fully covers the Sun from our view, it is called a _____________ solar eclipse.
Answer: It is called a total solar eclipse.
3. State whether True or False.
(i) Lunar eclipse occurs when the Sun comes between the Earth and the Moon.
Answer: False
Lunar eclipse occurs when the Earth comes between the Sun and the Moon.
(ii) Sunrise happens earlier in Gujarat than in Jharkhand.
Answer: False
Jharkhand lies further east than Gujarat, so sunrise occurs earlier there.
(iii) In Chennai, the longest day occurs on the summer solstice.
Answer: True
(iv) We should watch the solar eclipse directly with our naked eye.
Answer: False
Looking directly at a solar eclipse can seriously damage the eyes.
(v) Seasons occur due to the tilt of Earth's axis of rotation and its spherical shape.
Answer: True
(vi) The Earth's revolution around the Sun causes day and night.
Answer: False
Day and night are caused by the Earth's rotation on its axis.
4. Padmashree saw the Orion constellation nearly overhead at 8 PM yesterday. When will she see Orion overhead today?
Answer:
Stars appear about 4 minutes earlier every day because of the Earth's revolution around the Sun.
Therefore, if Orion was overhead at 8:00 PM yesterday, it will be overhead at approximately 7:56 PM today.
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?
Answer:
She will see the same group of stars rising at midnight again on or around 21 June of the following year.
This happens because the Earth completes one revolution around the Sun in about one year.
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?
Answer:
The Earth rotates on its axis from west to east. At any given moment, one half of the Earth faces the Sun and experiences day, while the other half faces away and experiences night. India and the USA are located in different parts of the Earth. Therefore, when India faces the Sun and has daytime, many parts of the USA are on the opposite side of the Earth and experience night.
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.
(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 was being careless because looking directly at the Sun during a solar eclipse can cause serious eye damage or blindness.
8. Fill in the circles in Fig. 12.18 appropriately with one of the following: Sun, Moon, Earth.
Image Source- NCERT
Answer:
Solar Eclipse:
Sun → Moon → Earth
The middle circle should contain Moon and the last circle should contain Earth.
Lunar Eclipse:
Sun → Earth → Moon
The first circle should contain Sun and the middle circle should contain Earth.
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?
Answer:
Although the Moon is much smaller than the Sun, it is much closer to the Earth. Because of this, the Moon and the Sun appear almost the same size in the sky. Therefore, when the Moon comes directly between the Earth and the Sun, it can completely block the Sun from our view and cause a total solar eclipse.
10. 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.
Australia lies in the Southern Hemisphere. In December, the Southern Hemisphere is tilted towards the Sun and experiences summer, while India in the Northern Hemisphere experiences winter.
11. Why do you think lunar eclipses can be seen from a large part of the Earth when they happen, but total solar eclipses can be seen by only a small part of the Earth?
Answer:
During a lunar eclipse, the Earth's shadow falls on the Moon. Since the Moon is visible from a large portion of the Earth's night side, many people can observe the eclipse. During a total solar eclipse, the Moon's shadow falls on only a small area of the Earth's surface. Therefore, only people within that narrow shadow path can observe the total solar 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.
Answer:
If the Earth's axis were not tilted, both hemispheres would receive nearly the same amount of sunlight throughout the year. The length of day and night would remain almost constant everywhere. As a result, there would be no significant seasonal changes such as summer and winter. The Earth would experience nearly the same climate throughout the year, and the seasons as we know them would not occur.