Solutions-NCERT-Class-7-Science-Curiosity-Chapter-12- Earth, Moon, and the Sun-CBSE

• Day and night occur because the Earth rotates on its axis.
• The side of the Earth facing the Sun experiences day, while the side facing away from the Sun experiences night.
• As the Earth completes one rotation in about 24 hours, day and night occur alternately.

Yes, stars also appear to move across the sky from east to west because of the Earth's rotation. However, since stars are very far away, their positions relative to one another seem almost fixed, unlike the Sun whose movement is more noticeable.

• Different stars appear in the night sky during different times of the year because the Earth revolves around the Sun.
• As the Earth moves along its orbit, the night side of the Earth faces different parts of space, allowing us to see different stars and constellations.

Yes, seasons are related to the Earth's revolution around the Sun.

As the Earth revolves around the Sun with its axis tilted, different parts of the Earth receive varying amounts of sunlight during the year. This causes the cycle of seasons such as summer, winter, spring, and autumn.

The two planets that revolve between the Earth and the Sun are Mercury and Venus.

• They can sometimes pass between the Earth and the Sun, but because they are much smaller than the Sun and are usually not perfectly aligned, they cannot block all of the Sun's light.
• Therefore, they do not affect the day-night cycle, seasons, or life on Earth.

Looking at the Earth–Sun position shown in figure :

• The North Pole is tilted away from the Sun.
• The South Pole is tilted towards the Sun.

This configuration corresponds to the December solstice (around December 21).

• At this time, the South Pole experiences 24 hours of sunlight (polar day).
• The North Pole experiences 0 hours of sunlight (polar night).

(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.,

(i) False : A lunar eclipse occurs when the Earth comes between the Sun and the Moon, blocking sunlight from reaching the Moon

(ii) False : Sunrise first occurs in the eastern part of India and then in other parts. Since Jharkhand is east of Gujarat, sunrise happens there first.

(iii) True

(iv) False : Directly viewing a solar eclipse must be strictly avoided, as the Sun is intense enough to damage the eyes and cause blindness.

(v) True

(vi) False : Day and night are caused by the Earth’s rotation on its own axis. The Earth's revolution around the Sun takes nearly one year and is related to the cycle of seasons.

Padmashree will see the Orion constellation overhead at 7:56 PM today.

Reasoning:

• We usually consider a day to be 24 hours long, but the Earth actually completes one full rotation on its axis in about 23 hours 56 minutes.
• Because of this, stars and constellations appear in the same position in the sky about 4 minutes earlier each night.
• So, if the constellation Orion was directly overhead at 8:00 PM yesterday, it will be overhead at about 7:56 PM today.

Nandhini will see the same group of stars rising at midnight on 21 June next year.

Reasoning:

• This cycle happens because the Earth rotates on its axis and revolves around the Sun.
• The Earth takes about 365 days and 6 hours to complete one revolution around the Sun.
• After one year, the Earth returns to nearly the same position in its orbit.
• Therefore, on the same date each year, we see the same stars and constellations in the night sky at the same time.
• As a result, the pattern of stars in the night sky repeats every year.

The reason for the time difference between India and the USA is the spherical shape of the Earth and its rotation on its axis.

• This difference occurs because the Earth rotates on its axis. At any given time, one half of the Earth faces the Sun and experiences day, while the other half faces away from the Sun and experiences night.
• India and the USA are located on opposite sides of the Earth. Therefore, when India is facing the Sun and it is daytime there, the USA is facing away from the Sun and it is night-time there. As a result, Abhay's uncle in the USA is usually sleeping when it is daytime in India.

Adithya was being careless.

Reasoning:

• Adithya's method is dangerous : Directly viewing a solar eclipse with the naked eye must be avoided, as the Sun's intensity is strong enough to damage the eyes and cause permanent blindness.
• Ravikiran's method is safe: Using specialized eye protection, such as solar eclipse goggles, is a recommended way to view the event safely.
• Jyothi's method is safe: Projecting the Sun's image onto a wall or screen using a mirror is a safe indirect viewing method.
• Aruna's method is safe: Attending a program organized by a planetarium or astronomy club is considered the "best way" to observe an eclipse, as these organizations provide scientific explanations and proper safety equipment.

• The Moon is able to block the Sun completely from our view during a total solar eclipse due to the concept of apparent size.
• The size an object appears to be to our eyes depends on both its actual physical size and its distance from the observer.
• Although the Sun is physically much larger than the Moon, it is also located much farther away from the Earth. The Moon, while much smaller in physical size, is much closer to us.
• Because of this difference in distance, the apparent sizes of the Moon and the Sun in the sky are very similar when viewed from Earth. This allows the Moon to appear large enough to cover the entire disc of the Sun when they align perfectly.

• The Indian cricket team should pack summer clothes. This is because December is summer in Australia.
• Reason : The Earth is tilted on its axis, and during December, the Southern Hemisphere (where Australia is located) is tilted towards the Sun and receives more sunlight. Therefore, Australia experiences summer, while India, in the Northern Hemisphere, experiences winter.

If the team travels to Australia in December, they should carry light summer clothing.

• A lunar eclipse can be seen from a large part of the Earth because the Earth's shadow is very large. When the Moon passes through this shadow, everyone on the night side of the Earth can see the eclipse.
• A total solar eclipse can be seen only from a small part of the Earth because the Moon's shadow is much smaller than the Earth's shadow. Only the places where the Moon's dark shadow falls can see the total solar eclipse.
• Therefore, lunar eclipses are visible over a much larger area of the Earth, while total solar eclipses are visible only from a narrow region.

If the Earth's axis were not tilted, there would be no seasons.

The Sun's rays would fall equally on the same regions throughout the year. As a result:

• Summer and winter would not occur.
• The length of day and night would remain almost the same throughout the year.
• Every place on Earth would experience nearly the same climate all year round.

Therefore, the change of seasons is caused by the tilt of the Earth's axis. Without this tilt, there would be no seasonal changes.