Tides Explained Simply
High and low tide (together: the tides) are caused mainly by the moon's gravitational pull on the ocean water.
On the moon-facing side and on the exact opposite side of the Earth, two water bulges (high tide) form at the same time. In between, at right angles to that, is low tide.
đź’¬ Mia asks Grandpa Theo
If the moon pulls the water towards it, why is there high tide on both sides of the Earth at once?
Because the moon-facing side is pulled the strongest, the Earth's center a bit less, and the far side the least. That difference "stretches" the water outward on both sides.
And why does high tide keep coming back, about twice a day?
Because the Earth rotates! Over the course of a day, every location on Earth passes through both water bulges and both "valleys" in between - that gives two high tides and two low tides.
The sun also pulls on the water, but with only about half the moon's force. When sun, Earth, and moon line up (at full or new moon), they reinforce each other into a spring tide. When they form a right angle (half moon), they partly cancel out into a weaker neap tide.