什麼是潮汐？
Tides are one of the most reliable things in the natural world. Just as we know the Sun will rise in the east and the stars will come out at night, we can be sure that the ocean will rise and fall along our shores.
Tides are very long waves that move through the ocean in response to the pull of the Moon and the Sun. They start in the open ocean and travel toward the coast, where we see them as the regular rise and fall of the sea.
When the highest part of the wave, called the crest, reaches a particular place, it is high tide. Low tide happens when the lowest part of the wave, called the trough, arrives. The difference in height between high tide and low tide is called the tidal range.
Tides play an important part in the natural world, and they also matter a great deal to people who work at sea, from fishers to ship captains.
潮汐是大自然中最可靠的現象之一。就像我們知道太陽會從東方升起、晚上會有星星出現一樣，我們也可以確定，海水會沿著海岸一漲一退。
潮汐其實是一種波長非常長的波，它在月球和太陽的引力作用下在海洋中移動。潮汐在大洋中形成，往海岸推進，我們在岸邊看到的，就是海水規律的漲退。
當波的最高處，也就是波峰，到達某個地方時，那裡就是滿潮；當波的最低處，也就是波谷到達時，就是乾潮。滿潮和乾潮之間的高度差，叫做潮差。
潮汐對大自然影響很大，對在海上工作的人，從漁民到船長，也都非常重要。