The Mystery of the Tides (4)

As you know, Uncle Ahab and Ernest have been n conversation about all things sailing. Ernest wants to sail and Ahab is just the man to teach him. Their sailing lessons continue and this time, they talk about tides…

“So, Ernest,” began Ahab, “this is the big question: what do you know about tides?” Ahab settled back, waiting for the explanation of what makes the sea go up and then go down again.

Ernest thought about this. “Well, not much but I do know,” he continued “that they have something to do with the moon!”.

“Excellent! But as sailors, we need to know a little more,” continued Ahab “And so today we are going to talk about tides.”

“You are right. Tides are caused by the gravitational attraction of the moon. In effect, the moon causes the world’s oceans to bulge out in the direction of the moon. But another bulge is caused on the opposite side as the earth is being pulled toward the moon. Because the earth is rotating, we get two tides a day.” explained Ahab.

“So, tell me, Ernest, why are the tides not at the same time each day? Why isn’t life simple and why don’t we have the same low tide and high tides every day?”

The silence was telling.

“Let me help you out. The earth is rotating, as we know, and it rotates along a given path with is not circular around the sun but slightly elliptical. This means that the moon is in different places at different times and so every day, the timing of high and low water changes. Get me?”

“It must be tough predicting tides then?” suggested Ernest

“Not really. Tides are a forced by the relationship between the earth, the moon and the sun. In the 21st century, we understand this relationship very well and so predicting where the moon and the sun are going to be and when means we can predict the tides with some accuracy.” replied Ahab, “But, there is a little bit of a problem on the horizon that some experts believe could change some of this.”

“Where?” as Ernest, standing to look at the horizon.

“Not literally Ernest! Hypothetically speaking,” continued Ahab, shaking his head. “Rising sea levels could cause some changes in tide prediction times but for the moment, this is not something we need to worry about.”

Ahab could see Ernest was thinking about something. After several minutes he asked, “I went on holiday to Spain and I swam in the Mediterranean but all the time I was there, the tide never went in or out. Why was that then?” asked a puzzled Ernest.

“The Mediterranean is a sea but you’re right, its tidal movement is tiny. This is because the sea is enclosed in a basin and thus, there isn’t a lot of room to move. Unlike our vast sea here. There is plenty of it to move.” Ahab continued, “we are going to talk more about tides because they are the things that stop us from sailing but also contribute sometimes to the swell and speed of the water beneath. We’ll talk more soon…”

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