The Earth is very big.  The Earth is in space.  The Earth is made of rock.  The Earth goes around the Sun.

Planets are very big.  Planets are in space.  Planets can be made of rock or gases.  Earth is a planet.  There are 8 planets in our Solar System.

A moon is made of rock.  A moon is very big.  A moon is smaller than a planet.  A moon goes around a planet.

Our solar system is in space.  Our solar system has a Sun, 8 planets and their moons.  The planets go around the Sun.

Space is very big.  All the planets, Earth, the Sun, and moons are in space!  Stars are in space.  Space is very, very bog.  There is no air in space.

Rock is very hard.  The Earth is made of rock.  Some planets are made of rock.  The moon is made of rock.

Air is a gas.  Gas can fill things up like a balloon, a tire, or a bubble.  A planet can be made from gas.

Rotate means to spin like a top spins.  A planet rotates.

Orbit means to go around.  A planet orbits a sun.  A moon goes around a planet.  This is called to orbit.  A planet orbits the Sun.