Day and night, and the phases of the Moon
Integrated ScienceEarth & SpaceAges 11–12
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Earth & Space
Viewed from above the North Pole: the Sun lights up half of Earth, Earth's spin creates day and night for the observer (red dot), and the Moon orbits Earth with its lit half always facing the Sun. The panel on the right shows the Moon's shape as seen from Earth — new moon, crescent, quarter, gibbous, full moon — changing day by day. Drag the Moon along its orbit to pick a phase, click Run/Pause, and change the speed. A 3D view lets you rotate the Sun–Earth–Moon scene: Earth spins with day and night, the Moon is lit by the Sun, and an inset shows the Moon's shape as seen from Earth.
Lesson: Apparent motion of the Sun (day and night); apparent motion of the Moon (the Moon's visible phases)
What it shows
Day and night happen because Earth spins on its axis once every 24 hours, carrying each place into and out of the half lit by the Sun. The Moon's phases have a different cause. The Moon is always half lit by the Sun, but as it orbits Earth, taking about 29.5 days from one new moon to the next, we see a changing fraction of that lit half. At new moon the Moon lies between Earth and the Sun; at full moon it is on the far side of Earth. Earth's shadow does not cause the phases.
How to use
Set the Viewpoint to show both views, press Run and follow the observer's local time to link Earth's spin to day and night. Then drag the Moon around its orbit and have students match each position with the shape seen from Earth, naming the phases in order. Choose a Starting phase such as Full moon to open a discussion, and lower the Simulation speed to follow a whole month. The 3D view lets students rotate the Sun–Earth–Moon system.
Parameters you can change
- Simulation speed 0.1–5 days/s
- Viewpoint Top view + view from Earth, Top view only (North Pole), Moon shape from Earth only
- Starting phase New moon, First quarter, Full moon, Last quarter
- Show phase name and day
- Show observer and local time
Questions to explore
- Where is the Moon relative to Earth and the Sun at full moon, and where is it at new moon?
- If the Moon is always half lit by the Sun, why do we see different shapes during a month?
- About how many days pass between one full moon and the next in the simulation?
