Tide
![High tide, Alma, New Brunswick in the Bay of Fundy, 1972Low tide at the same fishing port in Bay of Fundy, 1972](/Images/godic/202501/31/Bay_of_Fundy_High_Tide4827.jpg")
![Photo of boat resting on bottom next to dock](/Images/godic/202501/31/Bay_of_Fundy_Low_Tide4827.jpg")
![Schematic of the lunar portion of earth's tides showing (exaggerated) high tides at the sublunar and antipodal points for the hypothetical case of an ocean of constant depth with no land. There would also be smaller, superimposed bulges on the sides facing toward and away from the sun.](/Images/godic/202501/31/Tide_overview.svg4827.png")
![In Maine (U.S.) low tide occurs roughly at moonrise and high tide with a high moon, corresponding to the simple gravity model of two tidal bulges; at most places however, moon and tides have a phase shift.](/Images/godic/202501/31/Tide_and_Moon4827.jpg")
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth.
The times and amplitude of tides at a locale are influenced by the alignment of the Sun and Moon, by the pattern of tides in the deep ocean, by the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry (see Timing). Some shorelines experience a semi-diurnal tide - two nearly equal high and low tides each day. Other locations experience a diurnal tide - only one high and low tide each day. A "mixed tide"; two uneven tides a day, or one high and one low, is also possible.