Relationship Between Moon Phases & Tides

The moon is a natural satellite that orbits the Earth and has its own gravitational field. This field is strong enough that it affects the Earth, specifically water in the oceans. The side of the Earth closest to the moon will have a distinct bulge. The rise and fall of the ocean level results from the moon's gravitational field pulling as it moves in orbit around the Earth.

Tides

Tides are the rise and fall of the ocean water level at any given place. For six hours, a tide will rise on the beach. Then for six hours, the water level will recede into the ocean. Because oceans are liquid, their bulge is more obvious than the land bulge.

High Tides

The side of the Earth facing the moon will have a tidal bulge called the direct tide. Similarly, on the opposite side of the planet, the ocean will also be bulging. This is called the opposite tide. Therefore, high tides occur simultaneously on the opposite sides of the Earth.

Low Tides

Low tides are the receding waters between the high tides. In some places, low tide can be only a few feet while in others, the ocean can recede for miles. High and low tides both appear two times each in a 24 hour day, but, since the moon rises 50 minutes later each day, the tide cycles will differ by the same 50 minutes daily.

Spring Tides

The phase of the moon can also have an effect on tides. When the moon is at its full or new moon phases, the tides are the highest of their high tides and lowest of their low tides in their cycles than at other times. These highest of high tides are called spring tides. These can become even larger when the sun, moon and Earth all line up. The added gravity of the sun can make the oceans bulge even farther.

Neap Tides

During the moon's quarter phases, the sun pulls against the moon's gravitational pull instead of with it. During these tides, the result is the lowest high tide and the highest low tide. In other words, the least extreme difference between high and low tides. This is called a neap tide.

Perigee

If the moon is at perigee or the closest point in its orbit around Earth, the tides can be affected also. Combined with a full or new phase, the moon at perigee can produce the highest and lowest tides of all. Scientists can easily predict these highest of tides so warnings can be issued for possible coastal flooding.