Figure 1.0: Imagine a shell of the outer Earth , this diagram shows the Moon's gravity differential over the thickness of the shell.
1.1 Spring Tides and Neap Tides Spring tides are especially strong tides. 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. This very high tide occurs when the moon is both unusually close to the Earth (at its closest perigee, called the proxigee ) and in the New Moon phase (when the Moon is between the