Solar System — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Day and night happen because the Sun moves around Earth every 24 hours.
Corrected: Day and night happen because Earth rotates on its axis every 24 hours.
Earth spins on its own axis once every 24 hours, creating day and night. The Sun does not move around Earth — Earth rotates while the Sun stays in place at the center of the solar system.
2. Fix the sentence:
Seasons change because Earth moves closer to the Sun in summer and farther away in winter.
Corrected: Seasons change because Earth's axis is tilted, so different parts receive more direct sunlight at different times of year.
Seasons are caused by Earth's 23.5-degree axial tilt, not by distance from the Sun. When the Northern Hemisphere tilts toward the Sun, it receives more direct sunlight and experiences summer.
3. Fix the sentence:
The Moon produces its own light which is why we can see it shining at night.
Corrected: The Moon reflects light from the Sun which is why we can see it shining at night.
The Moon has no light of its own — it reflects sunlight. The bright glow we see at night is actually the Sun's light bouncing off the Moon's surface toward Earth.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Earth's axis is tilted at about 23.5 degrees, which causes the seasons.
Earth's axis tilts at about 23.5 degrees, and this tilt is what causes seasons by changing how directly sunlight hits each hemisphere throughout the year.
2. The Moon takes about 27 days to complete one orbit around Earth.
The Moon completes one orbit around Earth in about 27 days, which is called a sidereal month. It also rotates once in that same time, which is why we always see the same side.
3. When the Northern Hemisphere has summer, the Southern Hemisphere has winter.
Because Earth's axis tilts one hemisphere toward the Sun while the other tilts away, the seasons are opposite — when the north enjoys summer, the south experiences winter.
4. A full moon occurs when the entire sunlit side of the Moon faces Earth.
A full moon happens when the Moon is on the opposite side of Earth from the Sun, so its entire sunlit half faces us and appears as a bright, round disk.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Explain why it is daytime on one side of Earth and nighttime on the other side at the same moment.
Sample answer: Earth rotates on its axis, so the side facing the Sun receives sunlight and has daytime while the side facing away is in shadow and has nighttime.
Earth is a sphere that spins on its axis, so only the half facing the Sun gets lit at any moment. The lit side has daytime while the opposite side sits in Earth's own shadow, experiencing night.
2. Why does the Moon appear to change shape throughout the month?
Sample answer: As the Moon orbits Earth, we see different amounts of its sunlit side. The changing angle between the Sun, Moon, and Earth creates the phases we observe.
As the Moon orbits Earth, the angle between the Sun, Moon, and Earth changes. We see different amounts of the Moon's sunlit half depending on its position, which creates the cycle of phases from new moon to full moon and back.