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This is Yasin's 73rd original article
Happy Mid-Autumn Festival!
Today is the fifteenth day of the eighth lunar month, the Mid-Autumn Festival. First of all, I wish you all a happy Mid-Autumn Festival! Have you eaten mooncakes yet?
At the same time, today is Teacher's Day. The Mid-Autumn Festival is calculated according to the lunar calendar, and Teacher's Day is calculated according to the new calendar. These two festivals occur on the same day. This "coincidence" has only happened three times in this century, which is really rare. They are 2022, 2041 and 2079 respectively.
The origin of Mid-Autumn Festival
Why is it called "Mid-Autumn Festival" today? The word "Mid-Autumn Festival" first appeared in "Zhou Li". According to the ancient Chinese calendar, there are four seasons in a year, and each season has three months, which are called Mengyue, Zhongyue, and Jiyue. In mid-August, it is called "Mid-Autumn Festival". It was not until the early Tang Dynasty that the Mid-Autumn Festival became a fixed festival. The popularity of the Mid-Autumn Festival began in the Song Dynasty. By the Ming and Qing Dynasties, it had become as famous as New Year's Day and became one of the main festivals in our country.
About the origin of the Mid-Autumn Festival, there are roughly three: it originated from the worship of the moon in ancient times, the custom of singing and dancing under the moon to find even a couple, and the ancient custom of worshiping the land god in autumn. There is a saying: worship the sky in spring, worship the land in summer, worship the moon in autumn , and worship the sun in winter.
There are so many days in August, why is it August 15th? Because the Chinese lunar calendar is formulated according to the phases of the moon. On the 15th of each month, the moon "looks" at its fullest. As for why the fifteenth moon is the roundest? We will discuss this topic in more detail below.
Song Wu Zimu's "Meng Liang Lu": "August 15th is the Mid-Autumn Festival. This day is just halfway through the three autumns, so it is called Mid-Autumn Festival. The moonlight on this night is brighter than usual, and it is also called the moon night."
Getting to know the phases of the moon
The term "phases of the moon" is something I only recently learned about. One night when I was wandering outside, I suddenly looked up and saw the moon in the sky. The moon is big and bright, but its shape seems strange to me. It roughly looks like this:
This has subverted my cognition of nine-year compulsory education a bit. In my previous cognition (this cognition is wrong, but I have always thought so before, manual dog head here~), in the moon, the bright side is the reflection of the sun, and the dark side is the earth’s shade Lived the sun, cast shadows. Based on this cognition, the luminous part of the moon should only be concave inward, and such a shape cannot appear, because the earth is a sphere, and its shadow must be round, and the moon should be like this:
But the fact is that I saw the moon with the luminous part protruding outward with my own eyes. Based on my cognition above, I doubted the authenticity of this world at that moment, and even thought of the movie "The Truman Show". But I did a search online first.
First of all, I went to Zhihu, and I saw that someone had the same question as me, haha~
The respondent expressed sympathy (T_T). . . And use a sentence and a picture to explain the principle behind it. "The dark part of the moon is not the shadow of the earth, but the backlit part of the moon itself as a sphere . "
Frankly speaking, I never knew about this before. I thought it was because of the science I studied in high school (because the moon phase should belong to geography or astronomy), but I asked my cousin who studied liberal arts, and he said he didn’t learn it either. Pass. . .
If one day, a child points to the moon in the sky and asks you, why is the moon sometimes curved, sometimes round, sometimes concave inward, and sometimes convex outward? This is actually difficult to explain in practical language and requires some spatial imagination. The best thing to do is to use diagrams and experiment.
An interesting experiment is: use a flashlight (simulate the sun), put a basketball (simulate the moon), and then walk around the basketball (simulate the earth), you can see what the moon phase looks like in each position.
Detailed Moon Phases
Then I went to station b to see a more vivid and intuitive video explanation, and learned more about moon phases:
Among them, the new moon is generally on the first day of the lunar calendar. We cannot see the moon with the naked eye during the new moon. see". There are also the first quarter moon and the last quarter moon, they are all very nice~
The position of the moon is also different:
The cycle of the moon phase change is called "synodic month". A synodic month is about 29.53 days . The moon is at its roundest around fifteen).
So the real moon phase should look like this:
Through the understanding of the phases of the moon, I also understand why we can sometimes see the moon during the day, and the scene of "sun and moon shining together" appears.
solar and lunar eclipses
In fact, solar and lunar eclipses are caused by real "shadows".
The so-called solar eclipse means that the moon is between the sun and the earth, and the moon blocks the sun. The so-called lunar eclipse is between the earth and the moon, and the earth blocks the sun. Complete cover is called "total eclipse", the probability of occurrence is relatively small, and more parts are covered, called "partial eclipse".
The formation theory of solar and lunar eclipses will be more complicated. The orbital plane of the earth and the orbital plane of the moon do not coincide, but form an angle. This angle is approximately 5.3 degrees. If these two planes coincide, the earth will block the sun's light on the fifteenth day of each new moon and a lunar eclipse will occur, and the moon will block the sun's light on the first day of each month and a solar eclipse will occur. In fact, lunar eclipses and solar eclipses are not so frequent, because the light of this included angle is not blocked by the earth or the moon.
Although solar eclipses occur many times a year, they can only be observed in a narrow range of several dimensions and last only about 7 minutes. For a certain point on Earth, a "total solar eclipse" occurs only about once every 300 years. The shadow of the earth is projected on the moon, which is much larger than the moon (about 2.5 times the area), so lunar eclipses are very common and can last for about an hour. The number of lunar eclipses per year is generally two, at most three, and sometimes Not even once.
The sun and the moon look the same size
There is also a cold knowledge, why do we see the sun and the moon are about the same size when we are on the earth?
Because the distance between the sun and the earth is 400 times the distance between the moon and the earth, and the diameter of the sun is exactly 400 times that of the moon! Is this a coincidence or the handwriting of "God"? Of course, the orbits of the earth and the moon are not circular, but elliptical, so this distance is changing, but it looks roughly the same.
And because there is tidal friction between the earth and the moon, the moon is gradually moving away. Therefore, only in the last few billion years, the sun and the moon appear to be the same size on the earth, and we can see the beautiful annular solar eclipse. Hundreds of millions of years ago, the moon was closer to the earth than it is now, and the lunar disc was always larger than the solar disc, so there would be no annular solar eclipse. But hundreds of millions of years later, the moon was farther away from the earth than it is now, and the lunar disc was always smaller than the solar disc. There would be no total solar eclipse.
epilogue
This is a "popular science article", which roughly explains the origin of the next moon phase, lunar calendar, Mid-Autumn Festival, and solar and lunar eclipses.
I just want to sigh: the wisdom of the ancients is really great! By observing the moon, a set of scientific calendar was formulated to guide farming and sacrifices for thousands of years.
I also want to lament that the ocean of knowledge is profound and endless. In many cases, our cognitive level is far from enough to understand the truth of the world, but as long as we have a heart to explore, we will always be one step closer to the truth. Isn’t this how human beings keep moving forward?
Moreover, it is possible that many of your existing cognitions are wrong.
I’m also very surprised, I haven’t been exposed to this piece of knowledge since I was a child, it’s my knowledge blind spot, it seems that I’ve read less books, haha~
Did you know this knowledge before? How did you learn about it? You can leave a message to discuss in the comment area~
about the author
I'm Yasin, a techie who loves to blog
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