The moon goes around the earth once a month. Why is it that eclipses and eclipses do not occur every month?

When an eclipse occurs, the moon passes between the sun and the earth, blocks part or all of the sunlight, and casts its shadow on the earth. We see the solar eclipse. < / P > < p > we know that it takes 365 days for the earth to circle the sun at 5:48:46, which is very slow. The cycle of the moon around the earth is very short, and it only takes 29.5 days. In the process of rotation, the moon always passes through the middle of the sun and the earth, or passes through the other side of the sun and the earth. < / P > < p > we are familiar with the moon’s waxing and waning. In space, one half of the moon will be illuminated by sunlight, but the part of the moon that we see on earth will be different because of the change of the position of the moon around the earth. < / P > < p > this results in the fact that we often see a very thin crescent rising from the East on the night of the beginning of the lunar month. At this time, the moon is in a slightly easterly position between the sun and the earth, because the moon revolves counterclockwise from west to East. < / P > < p > in the next night, we will see that the moon will shift 12 ° in the sky every night at a certain time than the previous night, which is caused by the moon’s one-day orbit around the earth. < / P > < p > so it changes its position in the sky at the same time of night compared to the previous day, and the distance of 12 ° in the sky is about the width of a palm. < / P > < p > in the process of this change, the crescent will become bigger, fuller and brighter. When the moon moves from west to East and is perpendicular to the line between the sun and the earth, we will see a half illuminated and half dark moon in the sky. < / P > < p > the moon has changed from the first crescent to the half moon, that is, the upper dark moon. This is a month. After a quarter of the time, we will see a gradually round moon every night, becoming a waxy convex moon. < / P > < p > at the lunar month, we will see a full moon hanging high in the sky. This is what we can see from space. The moon is on the side of the sun and the earth, and the half of the moon illuminated by the sun can be seen by all the people on earth at night. < / P > < p > next, the moon will continue to move, and the process of the first half of the month will be repeated in the opposite way. The dark side of the moon will begin to swallow up the bright side, forming a waxy moon, a downward rotating moon, and a residual moon at the end of the month. At this time, the moon will return to the position between the sun and the earth, that is, from the end of the remnant moon to the beginning of the new moon of the next month, we can’t see the moon for a day or two. < / P > < p > this is because the moon is hidden in the dazzling light of the sun. At this time, the back of the moon is bright by the sun, but the side facing the earth in the daytime is dim, so it can not be seen. < / P > < p > in a day or two, the moon will move eastward, creating an angle. This is when people on earth will see the formation of a new crescent, and a new phase change will begin. < / P > < p > you should have noticed that there are two very special positions when the phase of the moon changes. That is to say at the beginning, the moon is in the middle of the sun and the earth. What if it blocks the sunlight? It’s a solar eclipse. < / P > < p > What if the moon is on the back of the earth? What if it enters the earth’s shadow? It’s an eclipse. Each month, the moon passes through these two locations, but it does not form a lunar eclipse or a solar eclipse. The reason is that when the moon moves around the earth, its orbital plane does not completely overlap with the earth’s orbit plane around the sun, but has an included angle. Take a look at the figure below < / P > < p > this angle is 5 degrees. Therefore, although the moon passes through these two positions every month, it does not form a special astronomical phenomenon, but most of the time it will fly above or below the sun and can not block the sun. < / P > < p > the same is true for lunar eclipses. Because of this angle, most of the time, the moon will miss the shadow of the earth and enter the shadow formed by the earth. Of course, we can’t see the eclipse. However, the orbit of the moon around the earth and that of the earth around the sun are not fixed. If you look at the earth moving around the sun and the moon moving around the earth, the change of the earth’s position will cause the moon’s orbit to rotate in space. < / P > < p > at least twice a year, the orbit of the moon will overlap with the earth’s orbit at these two special points, and then special celestial eclipses and eclipses will occur. Let’s talk about solar eclipses first. We all know that solar eclipses can be divided into three types: partial eclipse, total eclipse and annular eclipse. These three kinds are the moon’s shielding from the sun, but the different ways of shielding form three different kinds of sky phenomena. < / P > < p > when a partial solar eclipse occurs, no matter where you are on the earth, you will only see half of the sun blocked. Because the sun is very bright and rumored, even if the sun is covered by more than half, we will not feel the sky darken on the earth, nor can we observe it. We must use a professional sun filter to see it. < / P > < p > looking in space, we will find that the main reason is that the position of the moon is still a little biased. The umbra formed by the moon, that is, the dark shadow, has not been cast on the earth, but the penumbra has swept the earth. < p > < p > total eclipse, that is, the sun is completely blocked by the moon, and the sky becomes dark, just like night, and even the brightest stars in the sky can be seen. There are two necessary conditions for the occurrence of this kind of astronomical phenomena: first, the moon should be strictly in a straight line with the sun and earth; secondly, the moon is better to move to the perigee, so that the surface of the moon looks larger and can completely block the sun. < / P > < p > from space, we can see that the deep dark umbra cone formed by the moon under the sun’s illumination will cross a specific belt along with the rotation of the earth. In fact, the annular solar eclipse is the same as the total eclipse, except that the moon is not in the perigee, but is a little far away from the earth, so it can not completely block the sun, leaving a golden ring. < / P > < p > if you look from space, you will find that the umbra cone of the annular eclipse of the sun and the moon is a little short and can’t reach the earth, but it also delimits a specific belt area on the earth, which is the annular solar eclipse. People in other areas are still seeing a partial eclipse. < / P > < p > lunar eclipse is more simple, there is nothing to say, only partial eclipse and total eclipse, no annular eclipse. Because the shadow formed by the earth is very big, there is no situation that cannot cover the moon. The partial eclipse of the moon occurs before and after the total eclipse, that is, the moment when the moon is fully in or out of the earth’s umbra. A total eclipse, of course, is when the moon completely enters the dark shadow of the earth. Developed a “plug and play” solar power generation scheme, and “5B” won a $12 million round a financing

Author: zmhuaxia