how do tides occur

Tides are periodic short-term movements in the height of the ocean surface caused by a combination of the gravitational pull of the sun, the moon and the Earth’s rotation. Since the moon is closer, its gravitational forces are the primary driving forces for tidal fl uctuation. The moon literally pulls water towards it, creating a “bulge” facing the lunar surface. On the opposite side of the earth, another water “bulge” is created through lesser gravitational attraction. At right angles to the “bulges” are areas of less water. Since the water is pulled towards the moon, and opposite the moon, these depressions are created by a lack of water. As the earth rotates, a single point will move into a bulge of water, then into the corresponding depression. To an observer, the tide rises as the earth passes into a bulge, then recedes when the earth passes out of the bulge and into the depression. The sun can also exert some effect on the strength of the tidal cycle. If the sun and moon are in line with the earth, the combined gravitational attraction is greater and results in a spring tide. However, if the moon and the sun are at right angles to each other, a neap tide occurs. This explanation must also include some variation in tides due to land mass interference and basin shape. For these reasons, the Earth’s actual tides are either semidiurnal (two high and two low tides of nearly equal intensity each day), diurnal (one high and one low tide each day) or mixed (successive high or low tides are of differing intensity).

*picture show lowest tide at church reef, semporna, sabah