The moon - our nearest neighbour
Physics Narrative
for 5-11
A sphere with imperfections, reflecting light
The Moon is a sphere and it orbits the Earth. It is quite safe to look at the Moon, even through a telescope, because the light that comes from it is not very intense. The Moon reflects the light of the Sun – it is not luminous.
The Moon goes through phases so it seems to be different shapes at different times. A full cycle takes a month or moonth
. That's why from one full Moon to the next is one month.
The Moon always keeps the same side facing the Earth – the other side is the dark side
of the Moon. We never see the dark side from Earth and the only people who have seen it are the astronauts who have orbited the Moon.
It's a real coincidence that the diameter of the Sun is 400 times the diameter of the Moon but it is also 400 times further away! This extraordinary co-incidence means that the disc of the Sun, as we see it from the Earth, is almost identical in size to the disc of the Moon in the sky. The Moon can therefore just cover the Sun and obscure it completely during a total eclipse.
Phases – not for now
The reason for the shape of the Moon changing periodically, going through its different phases is tricky and widely misunderstood. This is not caused by the Moon being in the shadow of the Earth. It is caused by where the Moon is in relation to the Sun and the Earth and so how you see the Sunlight reflecting off the Moon. It really is best not to try to explain this to primary children. There is more on the phases of the moon in the SPT: Earth in space topic.