Phases of the Moon Explained — Answers
Answer sheet with model answers and success criteria for the Year 8 the solar system & space worksheet.
Success TutoringWorksheetsAnswer sheetYear 8 · Science · The Solar System & SpacePhases of the Moon Explained — Answers
Part A: Why does the Moon change shape?
Read the passage, then answer the questions.
The Moon does not make its own light. We see it because it reflects sunlight. The Sun always lights up half of the Moon — the half facing the Sun.
As the Moon orbits Earth, we see different amounts of that sunlit half. These changing shapes are called the phases of the Moon. One complete cycle of phases, the lunar cycle, takes about 29.5 days.
When the Moon is between Earth and the Sun, its lit side faces away from us and we see a new moon (almost nothing). When Earth is between the Sun and the Moon, we see the whole lit side: a full moon.
- AIt makes its own light.
- BIt reflects light from the Sun.
- CIt reflects light from Earth's cities.
- DIt glows because it is hot.
Answer: It reflects light from the Sun.
The Moon gives off no light of its own. We see sunlight bouncing off its surface.
- Anone of it at new moon
- Ball of it at full moon only
- Calways half of it
- Dit changes from a quarter to all of it
Answer: always half of it
The Sun always lights the half of the Moon facing it. The phase depends on how much of that lit half we can see from Earth.
- AEarth's shadow covering different parts of the Moon
- Bclouds blocking part of the Moon
- Cthe changing angle between the Sun, Earth and Moon as the Moon orbits Earth
- Dthe Moon spinning faster and slower
Answer: the changing angle between the Sun, Earth and Moon as the Moon orbits Earth
As the Moon orbits, we see different amounts of its sunlit half. Earth's shadow only falls on the Moon during a lunar eclipse.
Answer: 29.5
Also accept: 29 or 30 / about a month.
Part B: The eight phases
Waxing means the lit part we can see is growing; waning means it is shrinking. A crescent is less than half lit, a quarter looks exactly half lit, and a gibbous moon is more than half lit but not full.
Answer: new moon → waxing crescent → first quarter → waxing gibbous → full moon → waning gibbous → last quarter → waning crescent (→ new moon)
- waxing
- waning
- crescent
- gibbous
- quarter
- the lit part we can see is growing
- more than half, but not all, of the Moon's face looks lit
- the lit part we can see is shrinking
- less than half of the Moon's face looks lit
- exactly half of the Moon's face looks lit
Answer: waxing → the lit part we can see is growing; waning → the lit part we can see is shrinking; crescent → less than half of the Moon's face looks lit; gibbous → more than half, but not all, of the Moon's face looks lit; quarter → exactly half of the Moon's face looks lit
- Awaxing gibbous
- Bwaning gibbous
- Cwaning crescent
- Dnew moon
Answer: waning gibbous
After full moon the lit part we see starts to shrink (waning), but more than half is still lit (gibbous).
Answer: True
The name refers to a quarter of the cycle, not a quarter of the Moon being lit.
Answer: True
From there, the whole sunlit half of the Moon faces Earth.
Part C: Predict and explain
Answer: About 7 days
- The cycle is about 29.5 days and has four main phases.
- 29.5 ÷ 4 ≈ 7.4, so about a week
Answer: About 15 days
- Half a cycle: 29.5 ÷ 2 ≈ 15 days
- AWe see a different side of the Moon each night.
- BWe always see the same side of the Moon from Earth.
- CThe Moon has no phases.
- DThe Moon stays in the same place in the sky.
Answer: We always see the same side of the Moon from Earth.
Because its spin and orbit take the same time, the same face always points towards Earth. The far side is not always dark — it just never faces us.
Answer: False
The far side gets just as much sunlight as the near side over a cycle. At new moon, the far side is fully lit.
Model answer: This is wrong because at full moon, when Earth is between the Sun and the Moon, we see the whole Moon lit — Earth's shadow usually misses the Moon because the Moon's orbit is slightly tilted. If the shadow caused phases, a full moon would be dark. Earth's shadow only falls on the Moon during a lunar eclipse. The correct explanation is that the Sun always lights half of the Moon, and as the Moon orbits Earth we see different amounts of that lit half. At new moon the Moon is between Earth and the Sun, so its lit side faces away from us. At full moon it is on the far side of Earth from the Sun, so we see all of its lit side.
Success criteria:
- States the shadow idea is wrong with a reason (e.g. full moon position)
- Explains half the Moon is always lit by the Sun
- Describes positions at new moon and full moon correctly
- Links phases to the Moon's orbit
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.
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