Phases of the Moon Interactive Simulation

The Moon does not produce its own light — we see sunlight reflecting off its surface. As the Moon orbits Earth over roughly 29 days (the synodic period), we see different fractions of its sunlit face, creating the cycle of phases from New Moon (fully dark) through First Quarter, Full Moon, Last Quarter, and back. The illuminated fraction is determined purely by the Moon's orbital angle relative to the Sun–Earth line. Students can change day and compare what happens. Use it for earth science inquiry with Grades 3–5, Middle School, and High School on a projector or student device.

Standards: NGSS MS-ESS1-1

• Why the Moon appears to change shape over the month (orbital geometry, not shadow)
• How the illuminated fraction goes from 0% (New Moon) to 100% (Full Moon) and back
• Why First and Last Quarter moons are exactly half-lit (90° orbital angle)
• The difference between a waxing (growing) and waning (shrinking) moon
• Why we always see the same side of the Moon (tidal locking)

1. 1Predict how changing day will affect the illuminated, then test the prediction.
2. 2Use evidence from the interactive visual to explain the result.

Questions teachers ask