Discover why ocean water rises and falls along the world's coastlines.
Tides are the regular rise and fall of sea level caused mainly by the gravitational pull of the Moon and Sun. Coastal communities and marine life are often shaped by the rhythm of incoming and outgoing tides.
Learn how the Moon's pull helps create bulges of ocean water on Earth.
Learn MoreSee how the Sun adds to or weakens the Moon's tidal pull.
Learn MoreCompare the extra-strong and extra-weak tides that occur each month.
Learn MoreExplore how many coastlines experience two high tides and two low tides.
Learn MoreMeet the tough creatures that live where land meets sea twice a day.
Learn MoreDiscover how tides shape beaches, mudflats, and coastal habitats.
Learn MoreLearn how scientists forecast tides using data and mathematics.
Learn MoreThe Moon's gravity pulls on Earth's oceans, creating a bulge of water on the side of Earth facing the Moon. A second bulge forms on the opposite side of the planet because of the way gravity and motion balance across Earth. As Earth rotates, coastlines pass through these bulges, producing rising and falling tides.
The Sun is much farther away than the Moon, but it is so massive that its gravity also affects ocean tides. Depending on how the Sun, Moon, and Earth line up, the Sun's pull can strengthen or weaken the tidal bulges created by the Moon.
When the Sun and Moon line up during the new moon and full moon, their combined pull creates especially strong tides called spring tides. When the Sun and Moon are at right angles to each other, their pulls partly cancel out, producing weaker neap tides.
Many coastlines experience about two high tides and two low tides each day as Earth rotates. The exact timing and pattern of tides can vary between locations because of coastline shape, ocean depth, and other local factors.
The intertidal zone is the shoreline area that is underwater at high tide and exposed to air at low tide. Animals and plants living here, such as barnacles, mussels, crabs, and sea stars, must survive changing water levels, temperature, and wave action.
Tides help shape beaches, mudflats, salt marshes, and estuaries by moving sediment and water in regular patterns. Some coastal regions experience a large difference between high and low tide, while others have only small changes in water level.
Scientists can predict tides using data about the Moon, Sun, Earth's rotation, and local coastline features. Accurate tide predictions help sailors, fishers, and coastal communities plan activities such as navigation, fishing, and construction.