Lunar
Understand Moon phases through Sun–Earth–Moon geometry
Connect the Moon’s appearance with its position relative to Earth and the Sun. Explore phases and eclipse geometry across dates.
Key idea
Moon phases come from how much of the sunlit half we see from Earth. They are not normally caused by Earth’s shadow; that alignment produces a lunar eclipse. The orbital view helps separate these two geometries.
Try this first
Choose a date and compare the Moon’s illuminated appearance with the orbit view. Move time forward through part of a month and follow the changing Sun–Earth–Moon angle. Compare the phase with the geometry rather than memorizing its name alone.
How to get started
- Choose a date or drag the timeline; Now returns to the current moment.
- Compare the illuminated Moon with the orbital view to connect its phase with the Sun–Earth–Moon geometry.
- Explore the calendar and eclipse events, then open an event to examine its date and geometry.
Explore a little further
Try another experiment
Compare new Moon, first quarter and full Moon using the phase and orbit views. For each, identify the direction of sunlight and the side facing Earth. Explain why a quarter Moon looks half illuminated.
Good to know
Moon phases are not caused by Earth’s shadow; that is relevant to lunar eclipses. The app’s diagrams simplify size and distance so the relationships remain visible.
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