Question

(a) Explain why we always see the same side of the moon.
(b) Why does the moon change its shape daily?
(c) Suppose the moon emits light of its own. Would it still have phases? Justify your answer.
[4 marks]
[Exemplar]
[Moon, Phases of moon]

Answer 1

Solution:
(a) The period of rotation of the moon on its axis is equal to the period of its revolution around the Earth. This explains why we see the same side of the moon.
[1 mark]

(b) The Moon doesn't emit light itself. The moonlight we see is actually the Sun's light reflected off the lunar surface. Because of the Moon's changing position as it orbits our planet, the Sun's light focuses on different parts of it, making it seem that the Moon is changing shape over time.
[1 mark]

(c) No, the moon will not have phases.
[1 mark]

The phases are caused as the Sun illuminates different parts of the moon as it orbits Earth. If the moon emits light of its own, there will be no effect of light falling on the moon from the sun and we won’t observe phases.
[1 mark]