Tides are caused by the gravitational interaction between the Earth and the Moon. The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. Since the earth is rotating while this is happening, two tides occur each day. They occur when the Earth, the Sun , and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides.
Spring tides occur during the full moon and the new moon.
The eccentricity of the orbit of the moon in this illustration is greatly exaggerated. The Proxigean Spring Tide is a rare, unusually high tide. The proxigean spring tide occurs at most once every 1.5 years . Neap Tides Neap tides are especially weak tides. Neap tides occur during quarter moons.