Moon classroom
Why do Moon phases change?
Separate lunar phases from Earth’s shadow and explore the sunlit half of the Moon.
Half the Moon is illuminated
As the Moon orbits Earth, its sun-facing hemisphere is lit. From Earth we see different portions of that hemisphere. A thin crescent does not mean the Moon has shrunk.
Phases are different from eclipses
The dark part in ordinary phases is the Moon’s own night. An eclipse happens when a full Moon crosses Earth’s shadow. The tilted orbit prevents an eclipse every month. The experiment below models a cycle from 0 to 1; it does not predict actual dates.
Connect the model to the sky
Compare the model with today’s calendar and position. Fifty percent illumination describes the visible disk, not half of the entire surface. Its apparent orientation changes with location and time.
Reviewed: 2026-10-13 · Moon Where operator