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Highs are higher and lows are lower than at other times through the month. These more extreme tides, with a greater tidal range, are called spring tides. Spring tides occur when the tidal bulges from the Moon and Sun are aligned.
The Moon is full in this image; in the bottom image the Moon would appear as a new Moon. Neap tides are tides that have the smallest tidal range, and they occur when the Earth, the Moon, and the Sun form a 90 o angle Figure below. How do the tides add up to create neap tides? At neap tides, the tidal range relatively small. Neap tides occur when the Earth, the Sun, and the Moon form a right angle; the Moon is in its first or third quarter.
High tides occur about twice a day, about every 12 hours and 25 minutes. The reason is that the Moon takes 24 hours and 50 minutes to rotate once around the Earth so the Moon is over the same location 24 hours and 50 minutes later. Since high tides occur twice a day, one arrives each 12 hours and 25 minutes. What is the time between a high tide and the next low tide?
Some coastal areas do not follow this pattern at all. These coastal areas may have one high and one low tide per day or a different amount of time between two high tides. These differences are often because of local conditions, such as the shape of the coastline that the tide is entering. Skip to main content. The Ocean. Search for:. Tides Tides Wind is the primary force that causes ocean surface waves, but it does not cause the tides.
The Bay of Fundy has one of the greatest tidal ranges on Earth. The gravitational attraction of the Moon to ocean water creates the high and low tides. The tidal force causes water to bulge toward the moon and on the side opposite the moon. These bulges represent high tides. If the moon's gravity is pulling the oceans toward it, how can the ocean also bulge on the side of Earth away from the moon?
It does seem a little weird. It's all because the tidal force is a differential force—meaning that it comes from differences in gravity over Earth's surface. Here's how it works:. On the side of Earth that is directly facing the moon, the moon's gravitational pull is the strongest. The water on that side is pulled strongly in the direction of the moon. On the side of Earth farthest from the moon, the moon's gravitational pull is at its weakest.
At the center of Earth is approximately the average of the moon's gravitational pull on the whole planet. 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.
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