seegongsik
Grade 5 (age 10-11)

grade 5 Earth and Moon Motion

Earth spins once a day (rotation) and travels once around the Sun each year (revolution). As it spins, the half facing the Sun has day and the other half has night, so Korea passes through one day and one night every 24 hours. The Moon makes no light of its own, so only the half facing the Sun is bright; as it circles Earth we see more or less of that bright half, and its shape seems to change. In the first picture, change the time and watch when Korea moves into daylight. In the second, change the day and see where the Moon is when it shows each shape.

Rotation: why day turns into night

12:00
🌍 Why do we have day and night?
①Earth is a ball, so sunlight only ever reaches the half that faces the Sun.
②As Earth spins, Korea is carried through the bright half and then the dark half.
③One full spin takes about 24 hours, and that is the length of a day.
④Countries on the far side of Earth have the opposite, so when it is daytime in Korea it is usually night in the United States.

Why the Moon changes shape

15 d
🌙 Why does the Moon seem to change shape?
①The Moon gives off no light; it reflects sunlight, so the half facing the Sun is always the bright half.
②As the Moon travels around Earth, the part of that bright half that faces us changes from night to night.
③When the Moon is on the same side as the Sun, its bright side faces away and we cannot see it (new moon); on the opposite side, we see the whole bright side (full moon).
④Going through all the shapes and back takes about 29.5 days, close to one month.

What rotation and revolution do

Rotation and revolution
Rotation: Earth spins once (about 1 day) / Revolution: Earth circles the Sun once (about 1 year)
The picture shows only the spin, but the real Earth is circling the Sun at the same time.
💡 What rotation and revolution do
①Rotation turns day into night and back again once a day.
②Rotation also makes the Sun look as if it rises in the east and sets in the west.
③Revolution changes which constellations we see in the night sky from season to season.
④Seasons happen because Earth travels around the Sun with its axis tilted. Revolution alone would not give us seasons.

Summary

Earth and Moon in one view
Earth's rotation → day and night / Earth's revolution → seasonal constellations / Moon's revolution → Moon's shape
For the seasons to change, the tilted axis is needed as well.
🎯 Key points
①Earth rotates once in about 24 hours, which gives us day and night.
②Earth revolves around the Sun once in about 365 days.
③The Moon shines by reflecting sunlight.
④As the Moon goes around Earth, the bright part we can see changes, so its shape changes.
⑤The Moon goes new moon → waxing crescent → first quarter → full moon → last quarter → waning crescent, and after about 29.5 days it is new again.

Examples and Unit Test

Example 1
The Moon makes no light of its own, yet it looks bright at night. Why?
1
Unlike the Sun, the Moon is not a body that gives off its own light.
2
Sunlight hits the Moon's surface and bounces off into our eyes, so the Moon looks bright.
▸ Because the Moon reflects sunlight.
Only the sunlit side is bright, so how much of that bright side we see depends on where the Moon is.
Example 2
What does Earth's rotation cause, and what does its revolution cause?
1
Because of rotation, the side facing the Sun has day and the far side has night, so day and night swap once a day.
2
Because of revolution, we look out at a different part of the night sky, so the constellations change with the seasons. Together with the tilted axis, it also brings the change of seasons.
▸ Rotation → day and night / Revolution → seasonal constellations and the change of seasons
Rotation repeats every day; revolution repeats every year.
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 Earth rotates.
③Earth takes about one day to go around the Sun.
④The Moon looks the same shape all month.
⑤The day after a full moon, we see a crescent moon.
▸ ② Day and night happen because Earth rotates.
1
Earth rotates once a day, so the side facing the Sun has day and the far side has night.
2
The Moon reflects sunlight (①), one trip around the Sun takes about a year (③), the Moon's shape changes a little each day (④), and after a full moon comes the last quarter, the waning crescent and the new moon before a crescent appears again (⑤).
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