Earth, Moon, and the SunClass 7 Science NCERT Solutions
12 Solutions
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Solution 1 of 12
Q1Let Us Enhance Our Learning
In Fig. 12.17, how many hours of sunlight do the North Pole and the South Pole receive during one rotation of the Earth?
Solution
Based on the orientation shown in Fig. 12.17, the Northern Hemisphere is tilted towards the Sun.
- The North Pole is in constant daylight, so it receives 24 hours of sunlight.
- The South Pole is tilted away from the Sun and is in constant darkness, so it receives 0 hours of sunlight.
Q2Let Us Enhance Our Learning
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.
Solution
(i)
Stars rise in the East and set in the West.
(ii)
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 total solar eclipse.
Q3Let Us Enhance Our Learning
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.
Solution
(i)
False. A lunar eclipse occurs when the Earth comes between the Sun and the Moon.
(ii)
False. Jharkhand is to the east of Gujarat. The Sun rises in the East, so sunrise happens earlier in Jharkhand.
(iii)
True. Chennai is in the Northern Hemisphere, where the longest day is the summer solstice (around 21 June).
(iv)
False. It is extremely dangerous to watch a solar eclipse directly as it can cause permanent eye damage or blindness.
(v)
True. The text explicitly states that the tilt of the Earth's axis and its spherical shape are the reasons for seasons.
(vi)
False. The Earth's rotation on its axis causes day and night.
Q4Let Us Enhance Our Learning
Padmashree saw the Orion constellation nearly overhead at 8 pm yesterday. When will she see Orion overhead today?
Solution
Due to the Earth's rotation, stars appear to rise about 4 minutes earlier each day. Therefore, Padmashree will see the Orion constellation overhead at approximately 7:56 pm today.
Q5Let Us Enhance Our Learning
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?
Solution
The Earth completes one revolution around the Sun in approximately one year. After one year, the Earth will be back in the same position in its orbit. Therefore, Nandhini will see the same group of stars rising at midnight on 21 June of the next year.
Q6Let Us Enhance Our Learning
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?
Solution
The reason for this difference is the rotation of the Earth on its axis. The Earth is a sphere, and as it rotates, only one half of it faces the Sun at any given time, experiencing daytime. The other half is in darkness, experiencing night-time. India and the USA are located on different parts of the Earth, so when India is facing the Sun, the USA is on the opposite side, away from the Sun.
Q7Let Us Enhance Our Learning
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.
Solution
Adithya was being careless. It is extremely harmful to look at the Sun directly during a solar eclipse, as it can cause permanent blindness. The other methods are safe ways to observe a solar eclipse.
Q8Let Us Enhance Our Learning
Fill in the circles in Fig. 12.18 appropriately with one of the following: Sun, Moon, Earth.
Solution
The diagrams show the arrangements for solar and lunar eclipses.
- Top Diagram (Solar Eclipse): The arrangement is Sun, Moon, Earth. The Moon comes between the Sun and the Earth, casting a shadow on the Earth.
- Bottom Diagram (Lunar Eclipse): The arrangement is Sun, Earth, Moon. The Earth comes between the Sun and the Moon, casting a shadow on the Moon.
Q9Let Us Enhance Our Learning
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?
Solution
This is possible because of the concept of apparent size. The apparent size of an object depends on both its actual size and its distance from the observer. Although the Sun is about 400 times larger than the Moon, it is also about 400 times farther away from the Earth. This makes the apparent sizes of the Sun and the Moon in the sky almost identical when viewed from Earth, allowing the Moon to completely cover the Sun during a total solar eclipse.
Q10Let Us Enhance Our Learning
The Indian cricket team matches in Australia are often held in December. Should they pack winter or summer clothes for their trip?
Solution
They should pack summer clothes. Australia is in the Southern Hemisphere, where the seasons are opposite to those in the Northern Hemisphere. In December, when India (in the Northern Hemisphere) experiences winter, Australia experiences summer.
Q11Let Us Enhance Our Learning
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?
Solution
This difference is due to the size of the shadows involved.
- Solar Eclipse: The Moon is much smaller than the Earth, so it casts a small shadow (umbra) on the Earth's surface. Only people located within this narrow path of the shadow can witness a total solar eclipse.
- Lunar Eclipse: The Earth is much larger than the Moon, so it casts a large shadow that can cover the entire Moon. A lunar eclipse is visible to anyone on the night side of the Earth from where the Moon is above the horizon.
Q12Let Us Enhance Our Learning
If the Earth's axis were not tilted with respect to the axis of revolution, explain what would be the effect on seasons?
Solution
If the Earth's axis were not tilted, there would be no seasons. The Sun's rays would strike every location on Earth at the same angle throughout the year. The equator would always receive direct sunlight and be consistently warm, while the poles would always receive slanting rays and be consistently cold. The length of day and night would be 12 hours everywhere on Earth throughout the year (except at the poles). There would be no variation in the intensity and duration of sunlight, which is the primary cause of seasons.