Keep the sunlight fixed
The Sun lights approximately half the Moon at a time.
Moon Phase Explorer
Move the Moon around Earth and compare the sunlit portion seen by an observer.
Grades 3–5 · Earth Science
Your goal
Move the Moon to show full moon from Earth.
Reduced motion is on. The controls still update the scene.
Last quarter. 50% of the visible disk is sunlit. The Sun always lights half the Moon.
°
Phases come from our changing view of the sunlit Moon, not Earth's shadow. The orbit is seen from above the north side. The face view uses north up, so waxing light appears on the right. Southern views can look rotated.
Sizes and distances are not to scale. The Moon's tilted orbit usually takes it above or below Earth's shadow. This scene shows phases, not eclipses.
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Learn with Moon Phase Explorer
Moon Phase Explorer connects the Moon's orbit with the changing portion of its sunlit surface that we see from Earth. Move the Moon around Earth and compare the orbital diagram with the separate view from Earth. Students can investigate new moon, crescent, quarter, gibbous, and full moon positions. This elementary astronomy activity makes clear that ordinary Moon phases come from our changing view of the illuminated Moon, while Earth's shadow is involved in lunar eclipses instead.
What to look for
Change the viewpoint
As the Moon orbits Earth, an observer sees different portions of that sunlit half.
Separate phases from eclipses
Ordinary Moon phases are not caused by Earth's shadow.
For teachers and curious learners
Explain Moon phases using sunlight and viewing direction. Ask students to predict what will happen, change one setting, and explain what they observe. Learn gives a starting point. Practice and Challenge offer new goals with the same scene.
The orbit is drawn face-on and not to scale. The phase view uses a simplified observer orientation and omits eclipses, orbital tilt, and changing distances.
Continue with Moon Phases Explorer .