Why do the tides change anyway ?
The animation below shows the gravitational action of
the sun and moon on the earth's oceans, bringing this
dynamic process to life.
The world's oceans are in constant flux. Winds and
currents move the surface water causing waves. Ocean
levels fluctuate daily as the sun, moon and earth
interact. As the moon travels around the earth and as
they, together, travel around the sun, the combined
gravitational forces cause the world's oceans to rise
Imagine the earth covered completely by water. As the
earth spins, this water is balanced evenly on all sides
by centrifugal force. The moon has a gravitational pull
on this layer of water as it orbits the earth. This pull
causes the water to bulge toward the moon. Because the
earth is spinning there will be a bulge on the opposite
side of the earth as well.
As the earth rotates on its axis, each location on
the earth will experience both tidal bulges. The areas
of high water levels are high tides and the areas of low
levels are low tides.
Since the earth and the moon rotate around the sun,
there is an added modifying factor. When the sun and
moon are aligned, there are exceptionally strong
gravitational forces, causing very high and very low
tides which are called spring tides, though they have
nothing to do with the season. When the sun and moon are
not aligned, the gravitational forces cancel each other
out, and the tides are not as dramatically high and low.
These are called neap tides.
Tides vary from day to day. As the earth, moon, and
sun orbit, their positions constantly shift, causing
slightly different gravitational effects. This causes
the tides to occur at slightly different times. Tides
also vary from place to place. Geographical position
determines the level of tide. In Northern California
there are two unequal tides each day. In the Gulf of
Mexico there is only one high tide and one low tide each
Thanks to sfgate.com for the above. You can see
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