Moon phases · sunlight · orbit position · viewing angle
Learning outcomeExplain why the Moon appears to change phase as its orbital position changes.
Interactive 3D model
SunlightEarth / observerMoon orbit
Drag to orbit · Scroll to zoom
First quarter50% illuminated · 90° orbital position
Illuminated50%
Lunar age7.4 days
PhaseFirst quarter
What’s happening
The Moon is moving away from the Sun–Earth line. More of its sunlit half turns toward Earth, growing from a crescent toward first quarter. Its inclination only nudges the Moon above or below the reference plane.