Scientific rambling
As the saying goes: "The moon of fifteen is sixteen round", so is it the moon circle of fifteen or the moon circle of sixteen?
This question involves the way the moon changes, which is the "moon phase". The change in the phase of the moon is caused by the moon orbiting the earth, and the moon, as a satellite, does not emit light on its own, and the moonlight is the result of the moon's reflection of the sun's light. Because of this, the position relationship between the sun, the earth, and the moon determines the shape of the moon that we can see on the earth. The Moon orbits the Earth, so how long does it take for the Moon to orbit the Earth? Since movements are all relative, there are two answers to this question.
If the Sun is used as a reference, then the Moon takes about 27 to make one revolution around the Earth3 days, which is called the "sidereal month".
Yet it seems to us on Earth that 273 days is not enough for the moon to complete a change of profit and loss, this is because the moon is orbiting the earth at the same time, the earth is also moving in a circle around the sun, so if the earth is used as a reference, the moon must return to the extension line of the connection between the earth and the sun after a circle around the earth, which is considered to be a circle, at this time on the earth we see, the moon has completed a complete change of profit and loss, which is called the "synodic month", the time is about 295 days.
The lunar month used in China is determined according to the synodic month, which is divided into large and small months because the synic month is not a whole day.
The big month is 30 days, the small month is 29 days, and a big month plus a small month is exactly two weeks when the moon orbits the earth, which is two synodic months. During a synodic month, the Moon undergoes 8 different shapes. When the moon is located between the earth and the sun, the sun's light is completely blocked by the moon, and the side of the moon facing the earth is completely dark.
Later, as the position of the moon changes, we can see a curved crescent moon at night, and this form of the moon is called the "eyebrow moon".
After a few more days, the crescent moon gradually plumped up, and finally we could see the half moon, which is called the "first quarter moon". Later, the moon becomes larger, about three-quarters of the full moon, and the moon is called the "waxing gibbous moon". In 14After 75 days, the Moon finally came to the extension of the line between the Sun and the Earth, and the Full Moon appeared, and the Moon at this time was called "Mochizuki".
After looking at the moon, the moon begins to lose again due to the movement of the moon, and it once again takes on the form of a waxing gibbous moon, but at this time it is called a "waning gibbous moon".
After that, the half moon that appears again is called the "last quarter moon", and then it is reduced again to a curved crescent moon called the "waning moon", and finally the moon again comes to the middle of the sun and the earth, becomes invisible, and returns to the new moon, which is a complete synodic cycle. It can be seen that the moon is the time when the moon is at its fullest, that is, 14 after the new moon75 days. However, although the lunar month is established based on the synodic month, it does not completely overlap with the synodic month, and whether it is a 30-day large month or a 29-day small month, there is no guarantee that the fifteenth day will be the moon.
As a result, there is a phenomenon that the moon may appear not only on the fifteenth day of the lunar calendar, but also on the sixteenth day of the lunar calendar, and even on the fourteenth or seventeenth day of the lunar calendar.
It can be seen from this that it is not correct to say that the moon of the sixteenth must be rounder than the fifteenth, and the specific day of the moon is more round, depending on which day it happens to be the moon. In this case, why is there a saying that "the moon of fifteen is sixteen rounds"? In fact, the original meaning of this sentence has been misunderstood in the process of circulation, and the real meaning of this sentence should be: "the moon is round on the fifteenth and sixteenth days of the lunar calendar", not "the moon on the sixteenth lunar calendar is more round than the fifteenth on the lunar calendar". In fact, there are many common sayings that have been misunderstood in the process of circulation, such as cutting the hair in the first month as "thinking about the old", and as a result, it became the "dead uncle" in the first month, which made the uncle of the world have one more thing to worry about in the first month.