11. Keeping Time with the Skies
Complete solutions to Keep the Curiosity Alive. CBSE / NCERT Class 8 Science (Curiosity).
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Keep the Curiosity Alive
(i) We can only see that part of the Moon which reflects sunlight towards us. — True
(ii) The shadow of Earth blocks sunlight from reaching the Moon causing phases. — False
Phases happen because we see different parts of the sunlit half of the Moon as it moves around the Earth.
(iii) Calendars are based on various astronomical cycles which repeat in a predictable manner. — True
(iv) The Moon can only be seen at night. — False
The Moon can be seen in the daytime also on many days.
No.
A full Moon comes after about 29.5 days. So 12 lunar months make about 354 days. A solar year has about 365 days.
So the full Moon comes about 11 days earlier every year in the solar calendar. Amol’s birthday (6th May) will not fall on a full Moon day every year.
- Stars are shown on the dark part of the Moon. The dark part is still the Moon. It blocks the stars behind it, so no star can be seen there.
- The Moon is shown in front of a cloud, hiding it. Clouds are very close to the Earth, while the Moon is very far. So a cloud can hide the Moon, but the Moon can never hide a cloud.
(i) Write the correct picture label for each phase.
| Picture label | Phase of Moon |
|---|---|
| D | Three days after New Moon |
| E | Full Moon |
| A | Three days after Full Moon |
| C | A week after Full Moon |
| B | Day of New Moon |
(ii) List the picture labels of the phases that are never seen from Earth.
F. In a real phase, the line between the bright and dark parts always runs from one end of the Moon to the opposite end. In F, the dark part looks like a round bite taken from the edge. The Moon never shows such a phase.
(i) She saw the half Moon (first quarter). Its bright half faces the setting Sun in the west.
The half Moon overhead at sunset, lit on the western side.
(ii) The Moon is in the waxing phase (Shukla Paksha). About a week after new Moon, it is overhead at sunset, and it grows bigger on the following nights.
Kaushalya is telling the truth.
- A Moon rising in the East at sunset is opposite the Sun. Such a Moon is fully lit — it is the full Moon, not a crescent. So Ravi is not correct.
- A few days before full Moon, the gibbous Moon rises in the East in the afternoon. So Kaushalya is correct.
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Less often.
If the Moon moves slower, each lunar month becomes longer. Then 12 lunar months come closer to the 365 days of the solar year. The gap between the lunar year and the solar year becomes smaller. So the extra month (Adhika Maasa) will be needed less often.
Number of full Moons = 37
Suppose each month had only one full Moon. Then 36 months could hold only 36 full Moons. But there are 37 full Moons. So at least one month must have two full Moons.
This is possible because a lunar month (about 29.5 days) is shorter than most solar months (30 or 31 days).
Full Moon.
On the full Moon day, the Moon is opposite the Sun. It rises in the East at sunset and sets in the West at sunrise. So it stays in the sky the whole night.
The Earth takes about 365¼ days to go around the Sun. Without leap years, the calendar would slip by about 1 day every 4 years.
Years needed ≈ 180 × 4 = 720 years
So in about 700 years Independence Day would fall in winter.
- For communication — telephone, television and internet.
- For weather forecasting and warnings about cyclones.
- For navigation and finding locations (GPS).
- For studying the Earth — crops, forests, water and disasters.
- For space-science studies of the Moon, planets and stars.
(i) Day — one rotation of the Earth on its axis.
(ii) Month — one cycle of the phases of the Moon (about 29.5 days).
(iii) Year — one revolution of the Earth around the Sun (about 365 days).
Discover, Design, and Debate
The “Discover, design, and debate” projects are hands-on tasks. Do them with your classmates under the guidance of your teacher, and write your own observations.