The Sun, Moon, and Stars
Grade 3 · Science · Study Guide
Explore our solar system's star, Earth's natural satellite, and the night sky.
Look up on a clear night and you'll see thousands of stars — but the most important star for us is the one we can't look at directly: our Sun. The Sun is a massive ball of hot gas (mostly hydrogen and helium) that produces energy through nuclear fusion in its core. That energy travels 93 million miles to reach Earth and powers all life here — from warming the oceans to driving photosynthesis in plants.
The Moon is Earth's only natural satellite. It's about 238,855 miles away and orbits Earth about once every 27 days. The Moon doesn't produce its own light — what we see as moonlight is actually reflected sunlight. As the Moon orbits Earth, we see different portions of its lit side, creating the phases of the Moon: new moon, crescent, quarter, gibbous, and full moon.
The Moon's gravity affects Earth too! The Moon pulls on Earth's oceans, creating tides. When the Moon is closest, ocean water bulges toward it — that's high tide. The area away from the Moon gets high tide too, while the sides get low tide.
Stars are incredibly far away — even the next closest star to our Sun (Proxima Centauri) is so far that light takes over 4 years to travel here from it. Stars are organized into patterns called constellations. Ancient people used constellations for navigation and storytelling.
Key terms
- star
- A massive ball of hot gas that produces energy through nuclear fusion
- Moon
- Earth's natural satellite that orbits our planet approximately every 27 days
- orbit
- The path one object takes as it travels around another in space
- phases of the Moon
- The changing appearances of the Moon as seen from Earth during its orbit
- constellation
- A pattern of stars in the night sky given a name by ancient astronomers
Flashcards
- Sun
- The star at the center of our solar system; provides light and heat to Earth
- Moon
- Earth's natural satellite; orbits Earth every 27 days
- orbit
- The curved path an object takes around another in space
- phases of the Moon
- The changing shapes of the visible Moon throughout its monthly orbit
- constellation
- A named pattern of stars visible in the night sky
- satellite
- An object that orbits a larger body in space
Practice questions
What kind of object is the Sun?
- A planet
- A moon
- A star
- A comet
Show answer
Answer: A star
The Sun is a star — a ball of hot plasma powered by nuclear fusion. It's our closest star, about 93 million miles away, and the center of our solar system.
The Moon produces its own light.
Show answer
Answer: False
The Moon has no light of its own. We see it because it reflects sunlight back to us. A full moon reflects the most sunlight; a new moon reflects none toward us.
The path the Moon takes as it travels around Earth is called its ___.
Show answer
Answer: orbit
An orbit is the path an object takes due to gravity. The Moon's orbit takes about 27 days. Earth orbits the Sun in about 365 days.
What causes the phases of the Moon?
- Earth's shadow on the Moon
- Clouds blocking the Moon
- Different amounts of the lit Moon visible from Earth
- The Moon moving closer and farther from Earth
Show answer
Answer: Different amounts of the lit Moon visible from Earth
As the Moon orbits Earth, we see different portions of its sunlit side. A full moon means we see all of the lit side; a new moon means we see none of it.
Constellations are patterns of stars in the night sky.
Show answer
Answer: True
Constellations like Orion, the Big Dipper, and Cassiopeia are patterns that ancient cultures recognized and named. They help astronomers and navigators locate objects in the sky.
Fun facts
- The Sun is so large that about 1.3 million Earths could fit inside it!
- Footprints left by Apollo astronauts on the Moon will last millions of years because there's no wind to erase them.
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