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Spring Tides When the moon is full or new, the gravitational pull of the moon and sun are combined. At these times, the high tides are very high and the low tides are very low. This is known as a spring high tide. Spring tides are especially strong tides they do not have anything to do with the season Spring. 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. Neap Tides During the moon's quarter phases the sun and moon work at right angles, causing the bulges to cancel each other.

The result is a smaller difference between high and low tides and is known as a neap tide. Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another with respect to the Earth. Neap tides occur during quarter moons.

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 Sun and the Earth.

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The proxigean spring tide occurs at most once every 1. This is a time lapse of the tidal rise and fall over a period of six and a half hours. During the next six hours of ebb the fishermen unload their boats on the dock.

Effects of the Moon's Gravity

There are two high tides every 25 hours. The gravitational force of the moon is one ten-millionth that of earth, but when you combine other forces such as the earth's centrifugal force created by its spin, you get tides. The sun's gravitational force on the earth is only 46 percent that of the moon. Making the moon the single most important factor for the creation of tides. The sun's gravity also produces tides.

But since the forces are smaller, as compared to the moon, the effects are greatly decreased.

Keep up with Mother Nature

Tides are not caused by the direct pull of the moon's gravity. The moon is pulling upwards on the water while the earth is pulling downward. Slight advantage to the moon and thus we have tides. Whenever the Moon, Earth and Sun are aligned, the gravitational pull of the sun adds to that of the moon causing maximum tides. Spring tides happen when the sun and moon are on the same side of the earth New Moon or when the sun and moon are on opposite sides of the earth Full Moon.

When the Moon is at first quarter or last quarter phase meaning that it is located at right angles to the Earth-Sun line , the Sun and Moon interfere with each other in producing tidal bulges and tides are generally weaker; these are called neap tides. Offshore, in the deep ocean, the difference in tides is usually less than 1. In bays and estuaries, this effect is amplified. In the Bay of Fundy, tides have a range of Because the earth rotates on its axis the moon completes one orbit in our sky every 25 hours Not to be confused with moon's 27 day orbit around the earth , we get two tidal peaks as well as two tidal troughs.

These events are separated by about 12 hours. Since the moon moves around the Earth, it is not always in the same place at the same time each day. So, each day, the times for high and low tides change by 50 minutes. The type of gravitational force that causes tides is know as "Tractive" force. Why are there no ocean tides at the equator? For any particular location, their height and fluctuation in time depends to varying degrees on the location of the Sun and the Moon, and to the details of the shape of the beach, coastline, coastline depth and prevailing ocean currents.

The tidal bulge of the Moon follows along the path on the earth's surface which intersects with the orbital plane of the Moon. This plane is tilted about 23 degrees with respect to the equatorial plane of the earth. The result is that near the equator, the difference between high tide and low tide is actually rather small, compared to other latitudes.

To see this, draw a circle inscribed in an ellipse, with the major axis of the ellipse rotated by 23 degrees with respect to the circle's horizontal diameter. Now measure the height of the elliptical contour just above the 'equator' of the circle. You will see that it is quite small compared to other positions on earth, particularly at latitudes of 23 degrees or so. Even larger differences can occur depending on the shape of a bay or inlet or continental shelf. Also, like the surface of a vibrating drum, the world oceans have vibratory modes that get stimulated in changing ways from minute to minute.

Finally, there are storms at sea and elsewhere which move large quantities of water.

Detailed forecasts are available for high and low tides in all sea ports. The oceans are, of course, being periodically 'forced' by a number of tidal sources including the Moon and the Sun, but this forcing has a number of different periods and harmonics. The two dominant periods are sue to the Sun and Moon, these are referred to as the S1 and M2 'modes' which have roughly 12 hour periods because they raise TWO water tides on the ocean diametrically opposite each other.

But, for a variety of reasons, any given port will not have two high and two low tides each day; also called 'semi-diurnal tides'. A careful monitoring of the tides at any port for several years will show that in addition to the major modes, there are as many as minor or 'harmonic' modes as well. The World Ocean is a complex dynamical system. The natural velocity of a water disturbance depends on the depth and salinity of the water at each point it passes.

When bodies of land circumscribe bodies of water, they produce a collection of resonating systems that favor water oscillations with certain frequencies over others. The result is that the 'two high two low' tide rule can be strongly modified so that the time between successive high tides can be greater than or less that 12 hours in many cases. The result is that for some locations, there can be days when only one high tide occurs.

Looking at the Atlantic and Pacific Coast tide tables for , the data for the various 'Standard Ports' showed that virtually all days had two high tides and two low tides in San Diego, San Francisco, New York and Charleston. There were, however a few days every few months when only a single high tide occurred. Because tidal forces vary as the third power of distance, this little 8 percent change translates into 25 percent increase in the tide- producing ability of the Moon upon the Earth.

If the lunar perigee occurs when the Moon is between the Sun and the Earth, it produces unusually high Spring high tides.

It's Just a Phase: The Supermoon Won't Drive You Mad

When it occurs on the opposite side from the Earth that where the Sun is located during full moon it produces unusually low, Neap Tides. The gravitational pull of the moon acts even on these water bodies! Ram Kumar, Tenkasi, India There are. But most bodies of water are too small for the effect to be great.

Slightly longer days

On the other hand, check out the Great Lakes' tide tables. Peter Brooke, Kinmuck, Scotland Firstly, tides are not simply caused by the gravitational pull of the moon as such. The moon doesn't revolve around the Earth precisely. They both revolve around their mutual centre of gravity, but because the Earth is so much heavier this means that the moon travels in large circles while the Earth travels in very small circles.

It is this movement which causes the Earth's oceans, which are all interconnected, to "slosh" around, hence tides.

Lakes would be very slightly affected but they are extremely small in comparison with the world's oceans, and not interconnected so they can't slosh around so noticeably. Theoretically lakes must experience tides but the tides would be so small that even in the largest lakes the effect is masked by river inflows and wind and so on, all of which cause greater differences in water height than tides presumably must, so the latter are unmeasurable.

Michael Fisher, Brisbane, Australia The sloshing around is also caused by the bulge of water attracted by the pull of the sun and moon. As the earth rotates daily, the coast is dragged through the bulge, and so the water level rises and falls each day.