1. Vocabulary Moon, Earth, Sun

2. System A collection of parts working together to perform a job.

3. State of Equilibrium When the parts work together and the system is stable.

4. Cycle A series of events that happen one after another in the same order, over and over again.

5. Gravity The force that pulls things toward the center of earth or moon.

6. Satellite A heavenly body that moves in an orbit around another larger body.

7. Lunar Phases When the moon looks as if it is changing shapes but it is really reflecting various amounts of sunlight during each month.

8. Orbit The path an object takes to travel around another object.

9. Solar Eclipse When the moon passes directly between the Earth and the Sun which blocks our view of the Sun for a short while. Sun Earth Moon

10. Lunar Eclipse When the Earth passes directly between the Sun and the Moon briefly blocking out the Moon. Sun Earth Moon

11. Rotation The daily turning of an object around an axis.

12. Equinox When the midday Sun crosses the equator.

13. Solstice The time when the midday Sun is directly overhead at one of the tropics (Cancer, Capricorn)

14. Star A huge ball of hot gas in space.

15. Sun The vast fiery ball of gas – a star – that is nearest to Earth and which provides the Earth with energy.

16. Tide Rise and fall of ocean water level due to the moon’s gravitational pull.

17. Season Caused by the revolution of the Earth around the Sun. At certain times of the year, the Earth is closer to the Sun than at other times.