Tides are caused by the gravitational pull of the moon and sun on the Earth's oceans. This causes the ocean levels to rise and fall, creating high tides and low tides approximately every 12 hours on opposite sides of the globe. Spring tides occur during a full moon or new moon and have the highest tidal ranges, while neap tides happen midway between spring tides and have the lowest tidal ranges. Different types of tides are caused by the relative positions of the Earth, moon, and sun.