A system can be either closed or open: A closed system is a system that is completely isolated from its environment. ... An open system is a system that has flows of information, energy, and/or matter between the system and its environment, and which adapts to the exchange. I hope this helps .
It would depend where the moon is located around the earth. If it was in bewtween the sun and earth we would not ever see the moon, but if it was behind the earth we would see a full moon every night.