NCERT Solutions Class 8 Science Chapter 11 2026-27 PDF

Concept used. The Moon shines by reflecting sunlight. Moon phases happen because the Sun, Moon and Earth keep changing their relative positions. Earth's shadow causes a lunar eclipse, not regular phases. (i) True, (ii) False, (iii) True, (iv) False.

1. (i) is true because only the illuminated part facing Earth sends reflected sunlight towards us.
2. (ii) is false. Earth's shadow causes lunar eclipses, not the monthly phases of the Moon.
3. (iii) is true because day, month and year come from repeating astronomical cycles.
4. (iv) is false because the Moon can be visible in the daytime when it is above the horizon and bright enough.

Concept used. A birthday date in the Gregorian calendar follows the solar year, while a full Moon follows the Moon's phase cycle of about 29.5 days. These two cycles do not line up every year. No. His birthday will not fall on a full Moon day every year.

1. Amol's birthday date, 6 May, is fixed in the Gregorian solar calendar.
2. A full Moon repeats after about 29.5 days.
3. A solar year is about 365.25 days, which is not an exact whole number of Moon phase cycles.
4. So the full Moon date shifts in the Gregorian calendar from year to year.
5. Therefore 6 May may be a full Moon only in some years, not every year.

Concept used. The Moon is a solid object in space. Clouds are in Earth's atmosphere, and stars cannot be seen through the non-illuminated part of the Moon. Clouds are shown around the Moon, and stars are shown on the dark part of the Moon. Both are incorrect.

1. Clouds form in Earth's atmosphere, not around the Moon in space.
2. So drawing clouds very close to the Moon is incorrect.
3. The dark part of the crescent is still the Moon's surface.
4. Stars cannot be seen through that dark part because the Moon blocks the background sky.
5. Therefore the stars drawn on the dark part of the Moon are also incorrect.

Concept used. After New Moon, a thin waxing crescent appears. Full Moon is fully bright. After Full Moon, the Moon wanes, first as gibbous and then half Moon after about a week. (i) D, E, A, C, B. (ii) B and F are never seen from Earth as shown.

1. Three days after New Moon is a thin crescent, so it matches panel D.
2. Full Moon is the completely bright disc, so it matches panel E.
3. Three days after Full Moon is mostly bright but waning, so it matches panel A.
4. A week after Full Moon is about half illuminated, so it matches panel C.
5. Day of New Moon is dark from Earth, so it matches panel B.
6. Panel B is not visible from Earth on New Moon day, and panel F is not a normal Moon phase because its dark boundary is not the usual curved terminator.

Concept used. A waxing Moon is easiest to spot at sunset. When the Moon is overhead at sunset, it is about a week after New Moon and appears as a half Moon. Malini saw a half Moon. It was in the waxing phase.

1. At sunset, the Sun is near the western horizon.
2. A Moon overhead at that time is separated from the Sun by about a quarter of its orbit.
3. This corresponds to a half Moon shape.
4. Since it is seen well at sunset before Full Moon, the bright part is increasing.
5. So the Moon is in the waxing phase.

Concept used. A Moon rising in the east at sunset is nearly opposite the Sun and appears close to full, not crescent. A gibbous Moon can be visible in the afternoon in the eastern sky. Kaushalya is telling the truth.

1. When the Sun is setting in the west, an object rising in the east is nearly opposite the Sun.
2. The Moon appears full or nearly full when it is opposite the Sun.
3. So Ravi's crescent Moon rising in the east at sunset is not correct.
4. A gibbous Moon is more than half illuminated and can be far enough from the Sun to be seen in the eastern sky during afternoon.
5. Therefore Kaushalya's observation is possible.

Concept used. A luni-solar calendar adds an intercalary month when the lunar year falls behind the solar year. If the Moon's revolution becomes slower, lunar months become longer. They will need an intercalary month less often.

1. At present, 12 lunar months are about 354 days.
2. The solar year is about 365 days, so the lunar year is shorter by about 11 days.
3. An intercalary month is added to reduce this accumulated difference.
4. If the Moon revolves more slowly, one lunar month becomes longer.
5. Then 12 lunar months become closer to the solar year.
6. So the difference accumulates more slowly and an intercalary month is needed less often.

Concept used. If more objects are placed into fewer groups, at least one group must contain two or more objects. This is the pigeonhole idea. Three solar years have 36 months. Since 37 full Moons occur, at least one month must contain two full Moons.

1. A solar calendar has 12 months in one year.
2. In 3 years, the number of months is 12 × 3 = 36.
3. There are 37 full Moons in these 36 months.
4. If every month had at most one full Moon, only 36 full Moons could be placed.
5. But there are 37 full Moons.
6. Therefore at least one month must have two full Moons.

Concept used. A full Moon is nearly opposite the Sun. It rises around sunset and sets around sunrise, so it can be visible through the whole night. She would have noticed a full Moon.

1. If the Moon is visible from sunset to sunrise, it is in the sky all night.
2. An all-night Moon is nearly opposite the Sun.
3. When the Sun sets, a full Moon rises near the eastern horizon.
4. When the Sun rises, the full Moon sets near the western horizon.
5. So the phase is full Moon.

Concept used. Without leap years, the calendar would slip by about one day every four years because the solar year is about a quarter day longer than 365 days. Approximately 720 years.

1. A leap day corrects about one extra day every 4 years.
2. If leap years stop, the calendar shifts by about 14 day each year with respect to seasons.
3. To move Independence Day from August to winter, we need roughly a half-year shift, about 180 days.
4. Time needed =180 ÷ 14 years.
5. This is 180 × 4 = 720 years.

Concept used. Artificial satellites are human-made objects launched into orbit around Earth. They help us observe, communicate, navigate and study Earth and space. They are launched for communication, navigation, weather monitoring, disaster management and scientific research.

1. Communication satellites support television, telephone and internet services.
2. Navigation satellites help locate places and guide travel.
3. Weather satellites observe clouds, storms and other weather patterns.
4. Disaster-management satellites provide useful images and warnings.
5. Scientific satellites study Earth, the Sun, stars and other celestial objects.

Concept used. Time units came from repeating sky cycles: Earth's rotation, the Moon's phase cycle and Earth's revolution around the Sun. Day: Earth's rotation. Month: Moon's phase cycle. Year: Earth's revolution around the Sun.

1. A day is based on Earth's rotation, seen as the Sun returning to its highest position in the sky.
2. A month is based on the cycle of the Moon's phases, which takes about 29.5 days.
3. A year is based on Earth's revolution around the Sun and the cycle of seasons.