# Moon phases: the 3D book

> Turn the pages of a 3D book and watch the Moon, Earth and its shadow rise from the plates: why the Moon changes shape, with questions and a short quiz.

Canonical: https://spacesphere.sygnito.com/en/learn/book/moon-phases

Each night the Moon looks different: a sliver, a half, a full circle, then gone. Many adults will tell you it is Earth's shadow. And they will be wrong.

## 1. Half in sunlight, always

The Moon makes no light of its own: what we see is sunlight bouncing off its surface. And here is the key fact: the Sun always lights up half of the Moon, just as half of Earth is always in daylight. That sunlit half never goes away. What changes, night after night, is something else entirely: how much of that bright half happens to face us.

**Quick check:** How much of the Moon does the Sun light up at any moment?

- Only the part we can see
- Always half of it
- All of it during a full moon

## 2. A phase is a point of view

As the Moon travels around Earth, our viewing angle on its sunlit half keeps shifting. When the Moon sits between us and the Sun, its bright side faces away: we see almost nothing. That is the new moon. As it moves along its orbit, a sliver of the lit half comes into view, then more, until the whole bright side faces us: full moon. Then it narrows again. One full lap of this rhythm takes about 29.5 days: the same cycle you may remember as the Moon's calendar.

**Quick check:** Over several nights the Moon "grows" from a sliver to a full circle. What is really changing?

- The Moon's surface is brightening
- Earth is blocking less and less of it
- Our viewing angle on its sunlit half

## 3. It is not Earth's shadow

The most common wrong answer says Earth's shadow carves the Moon's shape. It does not. Earth's shadow touches the Moon only during a lunar eclipse: an event that happens a few times a year, not every night. The phases run on our changing viewpoint alone. Want proof you can check yourself? A full moon rises around sunset: when the Moon is opposite the Sun in the sky, we see its lit half completely, just as it climbs while the Sun sets.

**Quick check:** What does Earth's shadow actually do to the Moon?

- It causes an eclipse a few times a year
- It creates the phases each month
- It keeps the far side dark

## Quiz

**1.** Where do the Moon's phases come from?

- Our changing angle on the Moon's sunlit half
- Earth's shadow sweeping across the Moon
- Clouds passing in front of the Moon

**2.** During a new moon, where is the Moon's sunlit half?

- It disappears for a few days
- Earth is covering it
- Facing away from us, toward the Sun

**3.** A full moon is rising. Where is the Sun right about then?

- Right next to the Moon in the sky
- Setting on the opposite side of the sky
- Directly overhead

[Inspired by: Still Here, Techartist](https://iamtechartist.com/dinosaurs-to-birds/)

## Sources

- [NASA-M](https://science.nasa.gov/moon/moon-phases/)
- [NASA-E](https://science.nasa.gov/moon/eclipses/)

## Related

- [Learn](https://spacesphere.sygnito.com/en/learn)