20 October 2026
Why the moon changes shape
A kitchen-table experiment with a torch and an orange that explains the phases of the moon better than any diagram.
Bayo Adeyemi, learning team (example)
What you need
A torch or phone light, an orange or a ball on a stick, and a dark room. The torch is the sun, the orange is the moon, and your head is the Earth.
Doing it
Put the torch on a table at one side of the room, switched on. Hold the orange at arm's length and turn slowly on the spot. Watch the lit part of the orange as you turn. You will see a thin crescent, a half, a full orange and back again.
What is going on
Half of the moon is always lit by the sun. What changes is how much of that lit half faces us. When the moon is between us and the sun we see the dark side, the new moon. When we are between the moon and the sun we see the whole lit half, the full moon.
Take it further
Keep a moon diary for a month, drawing the shape each evening at the same time. Then check your drawings against the moon tool on our Sky tonight page. Children who do this rarely forget it.
Try it
Quick tips
Reader questions
Can I ask the author a question?
Yes. Send it in the chat or on WhatsApp and the author answers on the next Telescope Friday.
Can I use this at school?
Please do. The learning team can also run it as a workshop for your class.
