LITTLE QUESTIONS / MOON MAGIC, MEET SCIENCE

The Moon’s little
shape show.

Always round. A different view of its light.

The Moon stays round. Its phases change because, as it orbits Earth, we see different amounts of its sunlit half. Synchronous rotation keeps approximately the same face towards Earth. Ordinary phases are not caused by Earth’s shadow.

01 / LOOKING DOWN FROM NORTHYou move the Moon!

Time passed: 7.4 Earth days

Follow the pink marker: that side keeps facing Earth as the Moon turns.

Move the Moon around Earth

New MoonFull MoonNew again

Playback paceEarth and the Moon always slow down together.

Earth spins once per day relative to the Sun. About 29½ days pass from new Moon to new Moon. Everything is sped up together.

Read the science behind this exploration

Why does the Moon change shape?

The eight phases, in order: New Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, third quarter, and waning crescent. Waxing means the visible illuminated portion is growing; waning means it is shrinking.
The same face stays towards Earth: The Moon spins once per orbit relative to the stars. This synchronous rotation keeps its near side facing Earth. The space view and Earth view in this lesson use one shared, body-fixed crater pattern. A pink teaching marker shows the centre of the near side.
An orbit is about 27.3 days; a phase cycle is about 29.5: The Moon takes about 27.3 days to orbit Earth relative to the stars. New Moon to new Moon takes about 29.5 days because Earth also moves around the Sun. Earth’s daily spin is linked to the same elapsed time.
Phases and eclipses are different: Ordinary phases result from our viewing angle on the sunlit Moon. A lunar eclipse happens when the Moon passes into Earth’s shadow. The Moon’s tilted orbit usually carries it above or below that shadow.
What this diagram simplifies: The map looks from north and keeps the Sun on the left. It uses exaggerated sizes, parallel sunlight, a circular path and average speeds. Axis and orbit tilts, eclipses and libration are omitted. The Earth view is north-up; the Moon’s orientation in an actual sky varies with place and time. Craters are illustrative.

Sources: NASA: Moon phases ↗ · NASA: Tidal locking ↗

THE SAME FACE, ALL THE WAY AROUND

One trip around Earth.
One turn of the Moon.

The Moon turns as it travels. Those two motions keep the same side facing us. Watch the craters in the Earth view: the bright part changes, while the face stays the same.

BE A MOON DETECTIVE

Can you find a crescent?

Move the Moon until you see a little slice of light.

ONE LITTLE THING TO REMEMBER

The Moon stays round.
Our view changes.

The Moon doesn’t make its own light. It reflects sunlight. As it goes around Earth, we see different amounts of its sunlit half.

Earth’s shadow makes a lunar eclipse, a different event. The Moon usually passes above or below that shadow, so we can have full Moons without eclipses.

Explore light and shadows next ↗

For curious grown-ups

This map is viewed from the north and keeps the Sun on the left. It turns slowly with the Earth–Sun line; it is not a fixed view against the stars. Earth’s daily spin is linked to the same elapsed time as the Moon. The Moon’s spin stays synchronized with its orbit, keeping the near side facing Earth. Sizes and distances are exaggerated, and the path uses a circle at constant average speed. Axis/orbit tilts and eclipses are omitted to keep this diagram readable.

An orbit and a spin each take about 27.3 days relative to the stars. A phase cycle takes about 29.5 days because Earth also moves around the Sun. The Earth view is north-up; its orientation in your sky depends on location and time. Small real changes in the visible face, called libration, are omitted. The faint dark-side fill and pink marker are teaching aids; the crater pattern is illustrative.

Source: NASA: Moon phases ↗ · NASA: Tidal locking ↗