In my first post, I’m going to explain the phases of the Moon and how you can demonstrate them yourself at home. Over the course of about a month (29.5 days to be exact) the Moon orbits around the Earth and as it does it shows different “phases” but what causes these phases?
If we look at the image below we can see that on the left we have the Sun. The sun pours out huge amounts of light in the direction of the Earth and the Moon. However, the Moon does not produce light. The Moon acts as a giant mirror. If the Sun does not shine on the Moon we can’t see it.
At the start of the lunar cycle, the Moon is positioned between the Earth and the Sun. As we look from Earth we can only see a tiny piece of the Moon lit up. Most of the side we see is in darkness and this is called the New Moon. As the Moon moves around the Earth so that the Sun the Moon and the Earth form a right angle we can see half of the illuminated Moon and this is called the first quarter.
By half way through the cycle the Moon has moved all the way around to the other side of the Earth so that the Moon, Earth and Sun are in a straight line. We can now see the full illuminated side of the Moon or full Moon. The cycle continues and when the Moon forms another right angle with the Earth and Sun we see the third quarter.
Finally the Moon moves back into position between the Earth and Sun and the cycle starts again.
Demonstrating phases at home.
You can demonstrate the phases of the Moon yourself at home. You will need:
- A dark room.
- A torch.
- A ball such as a tennis ball.
Place the torch on a table or ask someone to hold it for you. The torch represents the light from the Sun. Stand a little away and hold the ball up so that it is between you and the torch. The ball represents the Moon. Check what part of the ball you can see lit up. Now move to your right and see what part of the ball is lit up. As you rotate around in a circle you should see the lit up portion of the ball changing.
Paul Smith 
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