# Moon Phases and Eclipses Simulation

> A free 3D model of Moon phases and solar and lunar eclipses for class: the real Moon on any date, its 5.1° tilt, the shadows, and real eclipses to jump to.

Source: https://olyclass.com/simulations/moon-phases-and-eclipses/ · Updated 2026-11-01

This simulation shows why the Moon has phases and why eclipses are rare. The Earth sits in the middle, the Moon moves along its real path for the date you choose, and sunlight comes from the Sun's real direction. A panel shows the Moon as you would see it from the Earth that night: its phase, how much of it is lit and how many days old it is. Switch to Eclipses to see the Moon's tilted orbit, the Earth's shadow and the Moon's shadow, and jump straight to real eclipses.

## How to use it

- **Phases:** the Sun is at the top. The yellow ring on the Moon marks the edge of the half the Sun lights; the dashed white ring marks the edge of the half facing the Earth. Where the two halves overlap is the part we see.
- **Seen from Earth:** the Moon as it looks in the sky, with north up for the Northern Hemisphere. Tap S to see it the Southern Hemisphere way, upside down.
- **Eclipses:** shows the Earth's orbit plane, the Moon's orbit tilted to it, the two nodes where they cross, and the shadows. The panel says whether this new or full moon makes an eclipse, and if not, how far it misses.
- **Time:** play at 1 hour, 6 hours or 1 day per second, choose a date, or step to the previous or next new moon, full moon or eclipse. The chips under Eclipses jump to real eclipses of 2026 and 2027.
- **Distance:** "Not to scale" draws the Moon 6 times closer (and bigger in Phases); in Eclipses its size, its height above the plane and the shadows stay true, so it meets the shadow when the real Moon does. "True distance" puts it 60 Earth radii away.
- **On a projector:** use the full screen button. Space pauses, N and F step to the next new and full moon (Shift goes back), E to the next eclipse.

## Why does the Moon have phases?

The Moon makes no light of its own. The Sun always lights one half of it, the half facing the Sun. As the Moon goes round the Earth, about once every 29.5 days, we see that lit half from a changing angle.

| Phase | Where the Moon is | What we see | Rises about |
|---|---|---|---|
| New moon | Between the Earth and the Sun | The dark half: nothing | With the Sun |
| Waxing crescent | A little east of the Sun | A thin curve, lit on the right | Mid-morning |
| First quarter | 90° from the Sun | The right half lit | Noon |
| Waxing gibbous | Between quarter and full | More than half lit | Afternoon |
| Full moon | Opposite the Sun | The whole lit half | At sunset |
| Last quarter | 270° from the Sun | The left half lit | Midnight |

After full moon the lit part shrinks in the same steps, now lit on the left (waning gibbous, last quarter, waning crescent). Left and right swap in the Southern Hemisphere.

The Moon goes once round the Earth in 27.3 days, but phases repeat every 29.5 days. While the Moon goes round, the Earth also moves along its orbit, so the Moon needs about two more days to line up with the Sun again.

## Why isn't there an eclipse every month?

A solar eclipse happens when the Moon passes between the Sun and the Earth and its shadow falls on the Earth. That can only happen at new moon. A lunar eclipse happens when the Moon passes through the Earth's shadow, which can only happen at full moon.

But the Moon's orbit is tilted 5.1° to the Earth's orbit plane. Most months the new moon passes above or below the Sun, and the full moon passes above or below the Earth's shadow. The orbit crosses the plane at two points called nodes. An eclipse needs a new or full moon close to a node. That lines up about twice a year, in "eclipse seasons" about 173 days apart, so every year has at least four eclipses and at most seven.

Lunar eclipses can be total, partial or penumbral (only the pale outer shadow). Solar eclipses can be total, annular or partial. The Moon and the Sun look almost the same size in our sky: the Sun is about 400 times wider but also about 390 times farther away. When the Moon is near its farthest point it looks a little smaller than the Sun, and a bright ring is left around it: an annular eclipse.

## Try this

Go to Eclipses and step through the full moons of 2026 with the Full moon button. Watch the Moon's height above the plane in the panel:

| Full moon (2026) | Moon's height | Eclipse? |
|---|---|---|
| 3 January | 4.3° above | No |
| 1 February | 2.3° above | No |
| 3 March | 0.4° below | Total lunar eclipse |
| 2 April | 2.9° below | No |
| 28 August | 0.5° above | Partial lunar eclipse |
| 26 October | 4.6° above | No |

The Earth's dark shadow at the Moon's distance is about 9,400 km wide, roughly 2.7 times the Moon's diameter, so the Moon has to pass within about 1° of the shadow's centre. Then press New moon a few times around 12 August 2026: the Moon passes 0.9° above the Sun's centre, close enough for its shadow to touch the Earth, giving the total solar eclipse seen from Greenland, Iceland and Spain.

## Teaching ideas

1. **Predict (3 min):** "The Sun lights half the Moon all the time. Why do we see a thin crescent some nights?" Collect ideas.
2. **Watch (5 min):** play at 1 day per second in Phases. Pause at each quarter and ask students to draw the Moon they expect, then compare with the panel.
3. **Explain (5 min):** point to the two rings. "Which half do we see? Which half is lit?" Students describe each phase as the overlap of the two halves.
4. **Puzzle (5 min):** "Why don't we get an eclipse every month?" Switch to Eclipses, step through the full moons in the table above, then compare a total and an annular solar eclipse with the chips.
5. **Review (10 min):** press "Make a review game" for a class game on the same screen, in teams, with your phone as the remote.

## Frequently asked questions

### Is the Moon in the simulation where the real Moon is?

Yes. Its position comes from the main terms of the lunar theory in Jean Meeus's Astronomical Algorithms. New and full moons match the published times to within a few minutes, and its eclipses match NASA's tables in date and type.

### Why do phases happen if the Earth's shadow doesn't cause them?

Phases come from where we stand. The Sun always lights half the Moon, and as the Moon goes round the Earth we see more or less of that lit half. The Earth's shadow only reaches the Moon during a lunar eclipse, at some full moons.

### Why don't we have a solar eclipse every new moon?

Because the Moon's orbit is tilted 5.1° to the Earth's orbit. At most new moons the Moon passes above or below the Sun and its shadow misses the Earth. An eclipse happens only when new moon falls near one of the two nodes.

### Why is the Moon red during a total lunar eclipse?

No sunlight reaches the Moon directly, but the Earth's air bends some sunlight into the shadow. On the way the air scatters the blue light away, as at sunset, so the light that reaches the Moon is red.

### Is it safe to look at a solar eclipse?

Only through certified eclipse glasses or a pinhole projector. Looking at the Sun, even when most of it is covered, can damage the eyes. During a total eclipse it is safe to look only in the short moment when the Sun is completely covered.

[Make a review game](https://olyclass.com/create?subject=science&grade=6&topic=Moon%20phases,%20solar%20and%20lunar%20eclipses)

## Credits

Moon and Earth maps: [Solar System Scope](https://www.solarsystemscope.com/textures/), CC BY 4.0, based on NASA data. Moon and Sun positions: the main terms of Jean Meeus, Astronomical Algorithms (chapters 25 and 47). Eclipse dates and types checked against NASA's eclipse catalogues (Fred Espenak).