🌓 Why the Moon changes shape

Round, half, a thin curve, then gone. Slide the Moon round the Earth and see why its shape changes every night.

What did you see last night?
Some nights the Moon is a bright round ball. Other nights it’s half, a thin curve called a crescent, nearly round (gibbous), or not there at all. Does the Moon really change shape?
Half in sunshine
The Moon doesn’t make its own light. Moonlight is sunlight bouncing off it. Like the Earth, one half of the Moon is always in sunshine, and the other half is dark.
Slide through a month
The Moon goes round the Earth, and the shapes come back every 29.5 days. Slide it round. As we see more of its sunny half it’s waxing; as we see less it’s waning.
Is it the Earth’s shadow?
Lots of people think the dark part is the Earth’s shadow. It isn’t! It’s just the Moon’s own night side. The Earth’s shadow only lands on the Moon in a lunar eclipse.
Same Moon, turned round
Everyone on Earth sees the same phase on the same night. But from the south, the Moon looks turned round, half a turn. Pick a place. (Its exact angle also depends on the time and where it is in the sky.)
The Moon right now (about)
Here’s the Moon’s phase right now, worked out on your device. It counts 29.5-day cycles from a new moon in 2000, so it can be up to a day out. It shows the phase, not whether you can see the Moon where you are.
Quiz time
It’s a full moon over London tonight. Make a guess, then fly to Sydney, on the other side of the world.
Guess, then try: What does Sydney see tonight? (A full moon / A half moon / No Moon at all)

⭐ Remember

The Moon is always half lit by the Sun.
As it goes round the Earth, we see more or less of that sunny half. Those are the phases.
It’s not the Earth’s shadow. Everyone sees the same phase, but from the south it looks turned round.

The globe pictures are simplified to show the idea. Earth images: NASA Blue Marble (public domain).