Why do we have two high tides in the same day?

Puzzlement. In most places on Earth, there are two high tides each day. Why is it so? To answer this, let's first turn to our usual suspects. In the mid-17th century, Galileo suggested tides were caused by the motion of water as Earth circled the around the Sun. read more

In between the two high tides are the low tides, and of course there are two of them as well. As a point on the Earth rotates under the high tide bulge, the water rises. A few hours later, when the Earth has rotated one quarter of the way around, that point is now under a low tide, and the water has receded. read more

Gravity at work in the Cornish fishing village of Mousehole, but it’s not the Moon’s effect alone that causes two high tides a day. – Getty Images When it comes to the effects of gravity, there are three major players we have to consider: the Earth, the Moon and the Sun. read more

Chris - As the planet turns, it's turning through both of those bulges of water, so you get high tide number 1, then it takes 12 hours to get round to the other side which is half a rotation, half a day, and there's the second bulge, second high tide. Dominic - Exactly, so. Those two bulges stay in the same place in space more or less on the line through the Earth to the moon, and the Earth is rotating once every 24 hours, so we move through one of those two bulges every 12 hours as you say. read more