Arrows represent the force of the moon's gravitational pull on Earth. To get the tidal force—the force that causes the tides—we subtract this average gravitational pull on Earth from the gravitational pull at each location on Earth. The result of the tidal force is a stretching and squashing of Earth.
This is what causes the two tidal bulges. Arrows represent the tidal force. It's what's left over after removing the moon's average gravitational pull on the whole planet from the moon's specific gravitational pull at each location on Earth. These two bulges explain why in one day there are two high tides and two low tides, as the Earth's surface rotates through each of the bulges once a day. The Sun causes tides just like the moon does, although they are somewhat smaller. When the earth, moon, and Sun line up—which happens at times of full moon or new moon—the lunar and solar tides reinforce each other, leading to more extreme tides, called spring tides.
When lunar and solar tides act against each other, the result is unusually small tides, called neap tides. There is a new moon or a full moon about every two weeks, so that's how often we see large spring tides. When the gravitational pull of the Sun and moon are combined, you get more extreme high and low tides. This explains high and low tides that happen about every two weeks. Note: this figure is not to scale. The Sun is much bigger and farther away.
If the Moon causes a high tide on one side of the Earth, what causes the high tide on the other side? The Earth is spinning, which is why we have night and day. These two high tides draw water away from the rest of the oceans, causing two low tides between the high tides.
The Sun, just like the Moon and the Earth, also has its own gravity which can affect the tides. It still does have an effect, though. So the Moon affects the tides because of gravity, but gravity from the Sun and the spinning of the Earth also change how the tides behave.
Read more: Curious Kids: Is there anything hotter than the Sun? 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. Fossils and dinosaurs.
Geology around the world. Earth processes. Get involved. Tides Tides are the daily or twice daily rise and fall of the oceans. Home Links Info for parents.
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