Moon Phase Simulator
The Moon never changes shape — we just see different amounts of its sunlit half. Drag through the 29.5-day cycle and watch the geometry and the view from Earth line up.
First Quarter
Sunlight always comes from the left
How it works
Half of the Moon is always lit by the Sun. What changes is how much of that lit half faces us.
When the Moon sits between Earth and the Sun we see its dark side: new moon. When Earth sits in the middle we see the lit face fully: full moon.
One full cycle takes 29.5 days — a little longer than the Moon's 27.3-day orbit, because Earth also moves around the Sun.
Fun facts
The Moon always shows Earth the same face, a effect called tidal locking.
A lunar month is 29.5 days, which is where the word 'month' comes from.
Waxing means growing; waning means shrinking.
The Moon drifts about 3.8 cm further from Earth every year.
