How Can the Moon Affect Tides?

Times of slack water

This link above provides a tutorial on how to use the official tide website. Once you are familiar with how it works, you can go directly to the tide website by clicking on the tide link at the top of the page.

How do the effects of the sun and the moon affect tide? The gravitational pull of the moon tugs on the surface of the ocean until its surface mounds up and outward in the direction of the moon. When the mound of water has reached its highest point it is called high tide. On the side of the earth opposite the moon, the centrifugal force caused by the earth's rotation produces another mound of water and high tide on the opposite side of the earth. Somewhere in between these two high tides are two flat areas on the surface of the ocean, these are low tides.

The moon appears to rotate around the earth each day, however it is the earth's rotation that gives this appearance. The moon actually orbits the earth in an elliptical pattern, taking 27.3 days to complete one orbit. The length of time that it takes for the earth to rotate around so that the moon is in the same position is actually a little over a normal 24 hour day. It is 24 hours and 50 minutes or a tidal day. That is why the tidal cycle starts approximately 50 minutes later each day. As the earth rotates, the moon’s gravitational force continually mounds the water and that fluid mound moves around the earth. The actual height of the tide is influenced by the shape of the coastline and depth of the water.

Two other areas that need to be covered are "spring tides" and "neap tides." It was mentioned previously that the tides are affected by both the sun and the moon. Actually, the sun's effect is less than half that of the moon but when these two bodies are in alignment and pulling in the same direction they cause higher high tides and lower low tides called spring tides.

On the other hand when the Sun and Moon are at right angles to one another with the moon pulling one direction and the sun pulling another there is somewhat of a canceling affect and you get lower high tides and higher low tides called neap tides.

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