How does the moon affect the tides?
How does the moon affect the tide?
We've all seen the moon in the night sky and heard people talk about how it affects the tides. But how exactly does the moon influence the ebb and flow of the ocean? In this article, we'll look at the science behind how the moon affects the tides, and how understanding this phenomenon allows us to predict tide times.
The moon is a powerful force on the Earth's oceans. Whilst the force of gravity exerted by the Earth is far greater, the Moon also has a gravitational field. It is close enough that it has some effect on the Earth but this mostly goes unnoticed. However, because water is easily moved the Moon's pull has a significant effect on the world's oceans.
The Moon's gravitational pull creates a bulge in the ocean on the side of the Earth closest to the moon called a high-tide bulge. A second bulge also occurs on the side furthest away from the moon, but this is caused by inertia. This is a little complicated to understand and outside the scope of this article. Basically the water here experiences less pull from the moon so is not drawn away, plus centrifugal force from the earth spinning pushes it out..
How these tidal bulges translate into high and low tides is quite simple in theory. I.e. the location of the bulge is where the tide is highest. And as the earth rotates the high tide bulge stays in place relative to the moon. So given there are two tidal bulges and the earth rotates once a day this equates to two tides per day. Roughly speaking this is correct, but there are other factors to take into account. For example, the earth's surface is not entirely ocean.
Also the moon isn't the only factor that affects the tides. The sun's gravitational pull also has an influence, but it is much weaker than the moon's – somewhere in the order of half, or less. In the same way the moon does, the sun's gravity causes two additional bulges in the ocean, one on the side of the Earth closest to the sun, and one on the side of the Earth farthest from the sun
It is this combination of the moon's and sun's gravitational pulls causes the tides to vary in size throughout the month. During a full or new moon, the gravitational pull of both the moon and the sun are aligned, creating the highest high tides and lowest low tides. This is known as a spring tide. During a first or third quarter moon, the gravitational pull of the moon and sun are perpendicular, creating smaller tides known as neap tides.
Understanding how the moon affects the tides can help us make better predictions of the ocean's behavior. With this knowledge, we can use tide charts to plan our fishing trips, beach visits, and other activities that involve the ocean. So the next time you're standing on the shore, take a moment to appreciate the powerful force of the moon, and how it affects the tides of the ocean.
How does a full moon affect the tides?
As explained above, it is both the sun and moon's gravitational pull which cause the tides. But what effect does the full moon have on the tides?
The full moon occurs when the sun, Earth, and moon are aligned. This means that the moon is on the opposite side of the Earth from the sun which illuminates the whole moon. When the moon is full, the gravitational pull of the sun acts on the tidal bulge on one side of the earth and the pull of the moon on the bulge on the far side. This combined gravity causes the tides to be higher than usual. These tides are called spring tides and are the highest tides of the month.
Neap tides are the tides that occur when the sun and moon are at right angles to each other. During neap tides, the gravitational pull of the sun and the moon are working against each other, which causes the tides to be lower than usual.
So, in short, the full moon causes spring tides - some of the highest tides of the month
Are tides higher during a full moon or new moon?
We have established that during a full moon the tides are higher because the sun, Earth, and moon are aligned which causes the gravitational pull of the sun and moon to combine. This combined gravitational pull causes the tides to be higher than usual.
Another alignment occurs during the new moon, except this time the moon is on the same side of the earth as the sun. The obvious effect is the moon's face is in shadow so we can barely see it, the other is a significant effect on the size of the tide.
As the moon and the sun are both on the same side of the earth, their gravitational pull is combined. In theory this greater, combined pull could make the tides during a new moon slightly higher than during a full moon. However, in practice there are a host of complicating factors that make this difference pretty negligible. For example, the alignment of the celestial bodies is rarely exact and even if it is, it might not occur at high tide.
Does moon cause high or low tides?
The moon does both. The moon's gravitational pull causes the Earth's oceans to bulge out on the side of the Earth that is facing the moon and the Earth's inertia causes an equal bulge on the opposite side. These are the high tide bulges.
Meanwhile on the ocean at a right angle from the moon the water level is suppressed which results in a low tide.
The moon's gravity is not the only force that affects the tides. The sun's gravity also affects the tides, but to a lesser extent. The sun's gravity causes the Earth's oceans to bulge out on the side of the Earth that is facing the sun. This bulge is called the solar tide. The solar tide is considerably smaller than the lunar tide.
Would there still be tides if there was no moon?
There would still be tides if there was no moon, but they would be much smaller than the tides we experience. The moon's gravity is the main factor in causing the tides, so without the moon, the tides would be the result of the sun's gravity alone. The sun's gravity is much weaker than the moon's gravity (less than half), so the tides would be much smaller.
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