Earth spins once a day, giving us daytime and nighttime.
As it circles the Sun each year on a tilted axis, the seasons change.
The Moon makes no light of its own, so as it orbits Earth its sunlit face shifts through crescents and a full moon.
Drag the sliders to turn Earth and move the Moon, and watch day, night, and phases appear.
Earth's Rotation — Day & Night
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Rotation & day-night — Earth turning makes day and night
12 h
🌍 Why do day and night happen?
①Earth turns once each day (rotation)
②Side facing the Sun = day, opposite = night
③One turn in 24 hours — so a day is 24 hours
④When Korea has day, the US has night
Why the Moon Changes Shape
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Lunar phases — moon changes shape over ~30 days
15 d
🌙 Lunar Shape Changes
①The Moon does not glow on its own — it reflects sunlight
②As the Moon orbits Earth, the visible lit part changes
③One full orbit takes about 30 days (a month)
④New → Crescent → First Q → Full → Last Q → Waning
What is Revolution?
Rotation vs Revolution
Rotation: spinning (1 day) / Revolution: orbiting the Sun (1 year)
Why does the Moon look bright at night? Does the Moon make its own light?
1
The Moon does not make its own light.
2
It looks bright because it reflects sunlight.
▸ It makes no light of its own; it looks bright by reflecting sunlight
The Moon reflects sunlight. Its shape looks different depending on its position around Earth.
Example 2
What does each of Earth's rotation and revolution cause?
1
Earth rotating once a day causes day and night.
2
Earth revolving around the Sun once a year causes the seasons to change.
▸ Rotation → day and night / revolution → seasonal change
Rotation (a day) makes day and night; revolution (a year) makes the seasons.
Unit-test style
Which statement about the motion of Earth and the Moon is correct?
①The Moon makes its own light
②Day and night happen because of Earth's rotation
③Earth's revolution period is about a day
④The shape of the Moon never changes
⑤A new moon comes the day right after a full moon
▸ ② Day and night happen because of Earth's rotation
1
As Earth rotates once a day, the side facing the Sun has day and the opposite side has night.
2
The Moon reflects sunlight (①), the revolution period is about a year (③), the Moon's shape changes over about 30 days (④), and after a full moon it returns to new through the waning phases (⑤).