Why the Moon changes shape.
Why does the Moon seem to change shape?
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Why does the Moon seem to change shape?
Move the Moon, then view its illuminated half from Earth.
Sunlight illuminates half the Moon. As the Moon orbits, an observer on Earth sees different fractions of that lit half. Full Moon is opposite the Sun in our sky. Earth’s shadow causes lunar eclipses, not ordinary phases.
Sun is far to the right. Illumination fraction (1−cos orbital angle)/2 from Earth; full Moon at 180°. Orbital size is schematic; eclipses are explained in a separate lesson.
Find the full Moon opposite the Sun.
Compare the Moon’s sunlit half with Earth’s view.