What Causes Tides?

Tides are caused primarily by the gravitational pull of the Moon (and to a lesser extent the Sun) on the Earth's oceans. As the Earth rotates, bulges of water follow the Moon, creating the rise and fall of sea level we call tides.

Most places around the UK experience mainly semi-diurnal tides — commonly two high waters and two low waters in a lunar day of roughly 24 hours and 50 minutes. A comparable tide is therefore often about 50 minutes later on average, but actual intervals vary by port and from one tide to the next, so use published predictions.