Q.How are tides caused?

Tides are caused by the gravitational pull of the Moon and, to a lesser extent, the Sun on Earth's oceans. The Moon's gravity pulls the water on the side of Earth facing it more strongly than it pulls the solid Earth, creating a bulge of water toward the Moon. On the opposite side, the Moon's pull is weaker, so the water lags behind, forming a second bulge away from the Moon.

As Earth rotates, different parts of its surface pass through these two bulges each day, producing two high tides and two low tides roughly every 24 hours. The Sun also contributes, though its effect is about half that of the Moon. When the Sun, Moon, and Earth align (at new moon and full moon), their pulls combine to produce higher-than-normal spring tides. When the Sun and Moon are at right angles to each other (at first and last quarter), their pulls partially cancel, giving low …

Think of the ocean as a vast, flexible skin stretched over the Earth. It does not sit perfectly still; it is constantly being tugged and squeezed by forces from space. The most important tug comes from the Moon, our nearest neighbour. Even though the Moon is small compared to the Sun, it is much closer, and closeness matters enormously in gravity. The Moon’s pull is about twice as strong as the Sun’s in raising tides. That is why the Moon, not the Sun, is the chief architect of the daily rhythm of the sea.

The key to understanding tides is to realise that gravity does not pull uniformly across the whole Earth. The side of the Earth facing the Moon feels a stronger pull than the centre, and the centre feels a stronger pull than the far side. This difference in pull is what we call the tidal force. It stretches the Earth slightly, and the oceans, being fluid, respond dramatically. On the side facing the Moon, water is pulled outward toward the Moon, creating a bulge. On the opposite side, something subtler happens: the Earth itself is pulled away from the water, leaving a second bulge behind. So there are two high tides at any moment, one facing the Moon and one facing away from it.

Now, the Earth rotates on its axis once every twenty-four hours. As it spins, different parts of the globe pass under these two bulges. A point on the coast experiences a high tide when it enters a bulge, then a low tide as it moves into the trough between bulges, then another high tide when it reaches the second bulge, and so on. That is why most coasts see two high tides and two low tides roughly every day, spaced about twelve hours and twenty-five minutes apart. The extra twenty-five minutes creep in because the Moon is also moving in its orbit, so the Earth has to rotate a little further to catch up with the same spot under the Moon. …