During the course of your day, the oceans are constantly moving. Every minute they are flowing, making the water rise and sink. This change in the level of the water is called the Tide. The tide moves verticly, or up and down, but if you did not have something to measure this against, you might not know it. On a beach though, one might actually see the tide creeping it's way up to your towel where you are laying. Often on beaches people move themsleves back, did you ever wonder why? Because the tide is rising. The tide rises and falls at a pretty steady rate. In some places there might be a tidal range of about three feet in around eight to twleve hours, but in places like the Bay of Fundy the range for the tides is as great as forty feet in about six hours! A Roman scholar, Seneca, realized that the basic motion of the tides had to do with the moon. When there were unusually high tides, he observed that the moon, earth and sun were all in line. We call the phase of the moon when this occurs, the new moon, or the full moon. During the new moon, you could look up in the sky for hours, but you would never see the moon. It is in between the earth and the sun, allowing no light to reflect off of it, so that we can't see it. A full moon is when the whole moon is lit up, a large bright circle in the sky, now the earth is in the center of the sun and the moon, and the moon is fully reflecting the suns rays back to us, we can see it perfectly. We refer to the rising tide as a flood, and the falling tide as an ebb. The word flood comes from a word used on a thirteenth century englishman's tide table, he uses the word flod. His tide table also proves that the tide follows the moon. In 1687, Issaic Newton dicovered what we refer to as Newton's Law of Gravitation. He claimed that everything was being pulled by the gravity of another object, and everything exerts it's own gravitational pull. In this way, the two largest heavenly bodies that are near to us, are the sun and the moon, therefore they are exerting gravitational pull, not only on the earth, but the tides. Because the ocean is a liquid, it is able to flow, the moon pulls the ocean, and the tides follow the moon. One might think that the Sun would rule the oceans, it's so large! Not so, though, distance also plays a part in gravity. The distance from the earth to the sun is 93,000,000 miles, the distance from the earth to the moon is only 239,000 miles. The moon is much closer to us, and so the Moon Control's the Tides. But exctly how does the moon control the tides? There are many parts the moon plays in controlling the tides, there are also parts played by other important forces, these are called the tide producing forces. High tide is basiclly when the moon is most over head. If we were to have a world with no land interfereing with the flow of tides, directly under the moon, the water would bulge towards it's pull. There is one high tide. At the excat oopposite of the earth there is another high tide there. Why, you say, would the water also bulge outward away from the pull of the moon? The reason for this is what we call centrifugal force. Centrifugal force tends to propel things outward. Centirfugal force, the motion of the earth's spin on it's axis, and the pull from the moon, overpowers the earth's gravity, and the water bulges out. There are normally two high tides during the day. So we said, the sun is a junior partner in the flow of the ocean, it's power is less than half the moon's, and all it basiclly does is increase or decrease the moon's power over the oceans. Everyday the tide rises fifty five minutes later than the day before. This has to do with the moon's revolution around the earth. The above was the fundemantals of tides, for more detailed information see the links.