Test the Moon

Explore Moon phases, eclipses and the way the Moon moves. Choose an experiment, change one setting and watch what happens.

Try the question

Why does the Moon change shape?

Move the Moon around Earth. Watch the Moon itself stay half lit while the phase seen from Earth changes.

Experiment Moon’s angle from the Sun 90°

What changed First quarter: 50% of the Earth-facing disc is lit, although half of the Moon is still in sunlight.

Watch for: The dark part is lunar night, not Earth’s shadow.

The dark part is lunar night, not Earth’s shadow.

Every experiment has a direct link

The string after ?state= is the learning contract. It chooses the model, starting position, control, task and observation without creating ten copies of the engine.

Why does the Moon change shape?What are the Moon phases called?Why is the phase month longer than one orbit?What does tidal locking actually mean?How can a locked Moon appear to wobble?Why does moonrise get later each night?Why isn’t there an eclipse every month?How much difference does Moon distance make?When can one month contain two full moons?Is the far side always dark?

What this model does and does not claim

These are explanatory models, not an ephemeris. Periods and tilt come from the same Moon and orbit constants used elsewhere on the site; the supermoon distance range is sampled from the site’s Moon solver. Sizes and separations are enlarged to keep the relationships visible.

For tonight’s real phase, rise time and distance, use the Moon pages. For the three bodies at a real place and instant, use the Sun, Moon and Earth movement simulator.