Intro to Moon phases (video) | Khan Academy
The gravitational forces of the moon, Earth and sun affect the ocean tides. Each day, four Relationship Between Moon Phases & Tides. Although it is often asserted that the moon "controls" the tides, this is really an as a consequence of rotation and gravity, with the moon being the factor that tips . sides of the Earth (full moon phase) or on the same side (new moon phase). Expect higher-than-usual tides in the days following the January 31, the first quarter and last quarter moon phase – when the sun and moon.
Likewise, the portion of the earth's oceans that are on the opposite side of the earth from the Moon are farther away from the moon than the earth's center, and the center of the earth will feel the greater pull and be pulled away from the ocean on the side opposite the moon. This forms a second bulge or high tide on the opposite side of the earth. As the earth rotates on its axis, the tides will move on the surface of the earth so that the high tide remains fixed on the side directly facing, and directly opposite the moon.
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Many other factors can affect the path taken by tides in each ocean basin, such as the shape of surrounding landmasses, but the dominant effect is from the moon's gravitational pull. The tides are generated by the gravitational pull of the moon on the Earth. It is tempting to think that the moon pulls on the ocean, which makes it rise slightly - and this rising of the ocean is interpreted as a high tide by folks on the Earth.
In this picture, as the Earth rotates under the moon, the high tide would appear to move - and you would see a high tide every 24 hours. It turns out, however, that high tide occurs every 12 hours! So this theory of the tides is definitely wrong. The way this really works is a little tricky. It is helpful to try to draw a picture of what I will try to describe for you.Seasons, moon phases, eclipses - Sun, earth, moon relationship review
It might also help to go get a book on the solar system that has a picture of this drawn for you so you can follow along. It's not that it's too hard to understand how the tides work; it's just that what is happening is very geometrical and hard to describe without pictures. So if you don't understand, it is definitely my fault. You probably heard that the gravitational force gets weaker as you get farther away.
This means that, things close to the moon get pulled with a higher force than things farther away from the moon. It is helpful here grab a piece of paper and draw a circle to represent the Earth, inside a larger circle that represents the surface of the ocean.
Now next to those two concentric circles, draw a smaller circle to represent the moon. As you can see from this diagram, the part of the ocean closest to the moon gets pulled with a stronger force than the Earth, which gets pulled with an even stronger force than the part of the ocean farther away from the moon.
If the gravitational force causes things to shift so that they are closer to the moon, the part of the ocean closest to the moon gets pulled farther than the earth which gets pulled farther than the far side of the ocean. The result is that the oceans look like they have been pulled away from the Earth on BOTH the side closest to the moon and the side farthest from the moon, implying that high tide occurs on opposite ends of the Earth at the same time.
Now, from the point of view of people on the Earth, the high tide appears to move as the Earth rotates, with a high tide occurring every 12 hours. As often happens in science, the details are a little more complicated. The basic picture, however, is correct.
The tides are due to the gravitational pull of the Moon and the Sun on the Earth. Because the gravitational force decreases as the distance squared, the part of the Earth that is closer to the Moon or the Sun is pulled a little extra and a bulge is created.
In addition, the other side of the Earth is pulled a little less than the center of the Earth so another bulge is created on the back side. As the Earth rotates about its axis, these bulges move along the surface of the Earth and causes what we call tides.
The tidal effect occurs because of the relative closeness of the Earth and Moon. The easiest way to picture the tidal effect is to consider the gravitational effect of the Moon on the earth. In particular consider the differential gravitational tug between a point on the surface of the Earth on the opposite side of the Earth- moon line and a point at its antipode that is, on the Earth surface directly under the moon.
A picture is worth a words but email media does not allow this. But if you look up tidal effects in almost any geology or astronomy book you will see the picture. At any rate,the near-side bulge on the earth is a direct consequence of the greater gravitational attraction by the moon compared to the center of the Earth.
The bulge at the opposite side results from the weaker attraction of the far side Earth point compared to the center A lot of people have trouble seeing this, but if you draw a diagram with force vectors of the appropriate lengths qualitatively and then add the opposite of the force of attraction between the moon and the center of the Earth, you will see that directly below the moon the residual force or the tidal force points directly towards the moon whereas on the opposite side the net force points directly away.
The ocean responds almost instantaneously to these forces because the viscosity of water is so low. The moon or any gravitational body, for that matter exerts agravitational pull that is stronger the closer you are to it. Since the Earth has a physical size, the gravitational pull on the Earth is stronger on the side facing the moon than it is on the side facing away from the moon.
Because the Earth is being pulled on more strongly on one side than from the other, it is effectively being stretched by the difference in the magnitude of gravitational force from the moon. Most of the Earth, of course, is solid it is made of rockbut the oceans are not, and, as a result, they are much easier to stretch than the solid Earth. Therefore, the liquid is pulled toward the moon more strongly on the side facing the moon, causing it to accumulate there, while the side opposite the moon, not feeling the moon's pull as strongly, stays on the side opposite the moon.
Because the ocean is still held by the Earth's gravity as well, it does not come off the surface, and instead sea level on the side of the Earth facing the moon and on the side opposite the moon rises. At the same time, sea level falls due to a relative lack of water halfway around the Earth from the moon.
This change in sea level is what we call tides. This right over here is a diagram from NASA's website.
Intro to Moon phases
And what you see here, clearly this is not at scale. This picture over here, this inner picture, the size of the moon and the earth is roughly at scale, but clearly the distances between them are not. You don't see thatmiles between them. In this inner circle, what you see is that the moon and the earth is always lit up from the right. So, it's assuming that the sun is 93 million miles in that direction.
And it is lighting up both the earth and the moon from the right. Now, as the moon rotates around the earth in its 28 day cycle, and if you're wondering, gee a 28 day cycle seems awfully close to a month, that is not a coincidence. The notion of a month comes from the cycles of the moon. In fact, even the word month and the word moon have the exact same root in old English. And in proto Germanic. They are essentially the same word.
But what you see is the moon goes in this 28 day cycle, when the moon is roughly between the earth and the sun, the lit up half of the moon is away from what we can see here on earth. And so, we see the non lit up side which would be a new moon. Now, as the moon goes, this is viewing from above the earth, this would be the North Pole right over here, as it goes counter clockwise as viewed from above the earth, we start to be able to see a little bit of that half of the moon that gets lit up.
So, when the moon is in this position, we see, us from earth, from this vantage point, we're able to see a little bit of the lit up side. When the moon is over here, we're able to see half the lit up side and half the non lit up side. And that's called a first quarter moon. And that keeps on going. When we're halfway through our cycle here, at a full moon, the earth is between the moon and the sun and so from our vantage point, we are able to see the entire lit up side. And that's why it is a full moon.
And then we keep going all the way until we get back to a new moon. Now, one question that might be bothering you, it bothered me for many years, is as soon as I understood this, the cycle of the moon, how the moon has this 28 day cycle as earth rotates around the sun, I always wondered well the new moon, it looks like the moon is between the earth and the sun, why doesn't it block out the sun every time we have a new moon?
Why don't we have a solar eclipse every 28 days?