Why is there two tides a day

These will come, but not until later in afternoon with the incoming tide. The kids are extremely confident of this fact. But my follow-up is tougher: how come there are two tides a day?

In most places on Earth, there are two high tides each day. Why is it so? In the midth century, Galileo suggested tides were caused by the motion of water as Earth circled the around the Sun. It was one of the rare occasions that Galileo got something wrong. Johannes Kepler, his German rival, was closer to the mark. Based upon ancient observations and correlations, Kepler thought the Moon must cause the tides.

Several decades later, Isaac Newton published his famous Principia. The book was most famous for describing the laws of gravity, and these same laws finally explained the tides. When it comes to the effects of gravity, there are three major players we have to consider: the Earth, the Moon and the Sun.

As a result, they end up in orbit around each other. Note: This animation is shown from the perspective of a viewer in the northern hemisphere. From a viewer in the southern hemisphere, the rotation would appear to go clockwise.

Welcome What are Tides? Why do these bulges exist? In a nutshell, they're primarily caused by the moon's gravitational pull upon the Earth. That force can have two separate components. It can pull matter "vertically," by which we mean perpendicularly to the Earth's surface.

And it can also pull things "horizontally" — i. Now, the spot on the globe that sits right beneath the moon at any given time is called the sublunar point. Meanwhile, the spot on the other side of our planet that is directly opposite the sublunar point is known as the antipodal point.

It's no coincidence that the ocean bulges are highest right over those two spots. At the sublunar point and the antipodal point, the moon's gravitational pull lacks a horizontal component — something that is also missing at the two corners of the world that are located 90 degrees away from these spots.

Those four areas are unique in that regard; every other location on Earth experiences a horizontal force that pushes water molecules in the ocean toward either the sublunar point where the moon's gravitational force is at its strongest or the antipodal point where the moon's gravitational pull is at its weakest. This is why the ocean bulges up over those two areas. Once every 24 hours, Earth completes a full rotation around its axis. During this process, any given spot on the planet's surface like, say, Long Island or Australia will pass right through both of those ocean bulges.

So — in most areas — when your home is directly under a bulge, the local tide should be high. But as it enters the space between the bulges, the tide in your area should get lower. This isn't always the case, as you'll learn next.

For now, let's discuss another factor that influences our tides. The sun also exerts a gravitational pull on the oceans , but because our solar companion is further away, its effects on the tides are less pronounced than the moon's. As the water rushes up the channel it sort of piles into these funnels and then as it gets narrower the wave gets higher. You actually get a high tide as the water rushes up. You get another one on the other funnel as the water rushes back down the channel so you get twice as many tides as you should have.

Go on a website called Nautide and look at todays forsact for tides. They note 4 x Low tides and 4 x High tides for today. Is there an explainatio. For that? The Earth is turning inside the orbit of the moon. And as the Earth turns, the gravitational pull of the moon causes water to heap up on the side of the Earth facing and the side farthest away from the moon; and as the planet turns, it turns inside that bulge, so the high tide happens twice, all around the world, during the day.

But, at the same time, remember that the moon is also in orbit around Earth, although it's making that journey quite slowly: it takes a month to complete a single orbit.

So, every day, the moon has moved a bit further along its orbital path, and therefore the time of day when a particular point on the Earth's surface is directly facing, or directly opposite, the moon's surface will be about an hour later than it was the previous day.

Hence the high and low tides occur about an hour later each day. Nearly every place in the world gets two high tides, two lows based on the lunar position.