NCERT Solutions: Earth, Moon, and the Sun

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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?

Ans: During one rotation of the Earth (24 hours), each pole experiences 24 hours of either continuous sunlight or continuous darkness, depending on the season. When the Northern Hemisphere is tilted towards the Sun (around June), the North Pole receives continuous daylight while the South Pole remains in darkness; six months later the situation is reversed and the South Pole has continuous daylight while the North Pole is in darkness. This long period of daylight or darkness at the poles is due to the tilt of Earth's axis, which keeps one pole tilted towards the Sun for about half the year.

Q2: Fill in the blanks

(i) Stars rise in the _________ and set in the ___________.

Ans: Stars rise in the East and set in the West.

(ii) Day and night are caused by the Earth's __________________.

Ans: 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.

Ans: When the Moon fully covers the Sun from our view, it is called a total solar eclipse.

Q3: State whether True or False
(i) Lunar eclipse occurs when the Sun comes between the Earth and the Moon. 

Ans: False
Explanation: A lunar eclipse occurs when the Earth is between the Sun and the Moon. The Earth's shadow falls on the Moon and blocks the Sun's light, so the Moon appears darkened.

(ii) Sunrise happens earlier in Gujarat than in Jharkhand. 

Ans: False
Explanation: Sunrise occurs earlier at places that are farther to the east. Jharkhand is east of Gujarat, so the Sun rises earlier in Jharkhand than in Gujarat.

(iii) In Chennai, the longest day occurs on the summer solstice. 

Ans: True
Explanation: The summer solstice (around 21 June) is when the Northern Hemisphere receives the most daylight. Chennai, being in the Northern Hemisphere, experiences its longest day around this time.

(iv) We should watch the solar eclipse directly with our naked eye.

Ans: False
Explanation: Looking directly at the Sun, even during an eclipse, can seriously damage the eyes. Special eclipse glasses or indirect methods such as projecting the Sun's image must be used to view a solar eclipse safely.

(v) Seasons occur due to the tilt of Earth's axis of rotation and its spherical shape.

Ans: True
Explanation: The tilt of Earth's axis makes sunlight fall at different angles on different parts of Earth during the year. Because Earth is spherical, these changing angles and the change in daylight hours cause the seasons.

(vi) The Earth's revolution around the Sun causes day and night.

Ans: False
Explanation: Day and night are caused by the Earth's rotation on its axis. As Earth spins, different parts face toward or away from the Sun, producing day and night.

Q4: Padmashree saw the Orion constellation nearly overhead at 8 pm yesterday. When will she see Orion overhead today?
Ans: She will see Orion nearly overhead about 4 minutes earlier than the previous day, so around 7:56 pm today. This happens because Earth moves a little along its orbit each day, so stars appear to rise roughly 4 minutes earlier each night.

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?
Ans: Stars rise about 4 minutes earlier each day, which adds up to one full day over a year. Therefore, Nandhini will see the same group of stars rising at midnight on 20 June next year - one calendar day earlier.

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?
Ans: This difference is because the Earth rotates from west to east, so different longitudes face the Sun at different times. India and the USA are at very different longitudes, so when it is day in India it is often night in the USA. Time zones are used so local clocks match the Sun's position in the sky.

Q7: Four friends used the following ways to see the solar eclipse. Who among them was being careless?

Ans:

• Ravikiran used a solar eclipse goggle - Safe
• Jyothi used a mirror to project the Sun's image - Safe
• Adithya saw the Sun directly with his eyes - Careless
• Aruna attended a programme arranged by a planetarium - Safe

Adithya was careless because looking directly at the Sun can cause serious and permanent eye damage; safe viewing methods must always be used.

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

Ans:

• Solar Eclipse: Sun - Moon - Earth

• Lunar Eclipse: Sun - Earth - 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?
Ans: Although the Moon is much smaller than the Sun, it is much closer to Earth. Because of this difference in distance, the Moon and the Sun appear almost the same size in our sky, so the Moon can cover the Sun completely during a total solar eclipse.

Q10: The Indian cricket team matches in Australia are often held in December. Should they pack winter or summer clothes for their trip?
Ans: They should pack summer clothes. December is summertime in Australia because it is in the Southern Hemisphere, so the weather is generally warm. It is sensible to carry light clothing and sun protection; in some regions evenings can be cooler, so one light warm layer may also be useful.

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?
Ans: During a lunar eclipse, the Earth casts a large shadow that falls on the Moon. This shadow can be seen from anywhere on Earth where the Moon is above the horizon, so a large region of the night side can observe the eclipse. In a solar eclipse, the Moon casts a much smaller shadow on Earth; only the narrow path of the Moon's full shadow (the path of totality) sees a total eclipse. Outside that narrow path people see only a partial eclipse or none at all.

Q12: If the Earth's axis were not tilted with respect to the axis of revolution, explain what would be the effect on seasons?
Ans: If Earth's axis had no tilt, there would be no seasons as we experience them now. Each place would receive nearly the same angle of sunlight and the same length of day throughout the year, so temperature and daylight would remain almost constant from month to month. Any small changes in climate would be due only to Earth's distance from the Sun, not to changing sunlight angles.