The saying "the moon on the fifteenth day is sixteen circles" may have been heard by everyone, and the meaning is also very clear. The moon on the fifteenth day may be sixteen circles, but people pay more attention to the moon on the sixteenth circle; In fact, it is possible for the full moon to occur on 14, 15, 16 or even 17, but have you ever thought about why such a phenomenon occurs? The following is the information I collected. Let's have a look!
The moon's sixteenth circle on the fifteenth is an astronomical phenomenon. When the new moon appeared relatively late on the first day of the new year, Wang appeared on the 16th. Even seventeen. The moon's fullest and brightest moment is when it looks. What is "Hope"? On the first day of the lunar calendar, the moon moves between the earth and the sun. The illuminated hemisphere of the moon carries the earth behind it. We can't see the moon. It's called "new moon" or "new moon"; On the evening of the 15th and 16th of the lunar calendar, all the bright sides of the moon face the earth, so we see the moon as round as a jade plate, "full moon" is also called "Hope".
In short, due to gravity, the speed of the moon's revolution around the earth is sometimes fast and sometimes slow. The average period from "new moon" to "new moon" or from "Hope" to "Hope" is 29.53 days, but the difference between the longest period and the shortest period is about 13 hours. If the moon shines slowly before "Hope", it may take 16-17 days from "new moon" to "Hope", Therefore, there will be a situation of "the moon is 16 circles on the 15th, and sometimes even 17 circles".
Some friends with astronomical knowledge may know that the moon has been locked by the earth's tide, and its rotation and revolution cycle are consistent. The time of circling the earth is less than a few days a month. To be precise, it should be 27.32166 days. Things suddenly become clear, because if there are only 27 days in a month, if it is a new moon at the beginning of the lunar month (the time when the moon cannot be seen in full darkness), then the moon watching (the full moon time) should take place on Nong 13, The next new moon should be the 27th day of the lunar calendar. Is that true?
Changes in the phase of the moon
It does seem so. No problem at all? From the above figure, the lunar phase change experienced by the moon during its revolution is completely in line with the change of light lunar phase in the astronomical sense, but why is the law of new moon observation nearly half a day in half a month (calculated according to the first 14th lunar month), and nearly three days in less than a month? Is there a problem with our common sense?
In fact, if the earth doesn't move in its orbit, there is no problem with the phase change of the moon in the above figure, but the earth doesn't gallop in its orbit at a speed of nearly 30km / s per second. (the above figure is only the new moon chart from the stellar monthly cycle). If the influence of revolution is added, the phase position of the moon should be understood as follows:
Genesis of moon watching plastic
If the corresponding position at point a is the new moon, and the earth and the moon are in the same straight line, then the earth's position reaches point B in the second month, and the moon at the same position is no longer the connection between the earth and the sun, branching out at a relatively large angle. The moon needs to rotate another angle to become the new moon again, and this angle difference requires 2.21 days to reach the moon!
Stellar month: the theoretical phase change of the moon's rotation cycle is a stellar month cycle. The stellar month does not consider the change of the relative position between the earth and the sun. The time of a stellar month is 27.32166 days
Lunar New Moon: the profit and loss cycle of the lunar phase considering the influence of the earth's revolution. A lunar new moon cycle is 29.53059 days
The lunar calendar takes the new moon as the cycle, but there is no half day. Therefore, the size of the lunar month is 29 days and 30 days. Therefore, the cumulative difference will lead to the cycle of the full moon. It will not be on the 15th day of the lunar calendar every time, but it will change slightly in that range!
In addition, this will lead to another problem. By the way, the twelve new moon cycles of the lunar calendar are one year. According to this calculation, there are only 354.3667 days a year, which is about 11 days different from a regression year (the earth's revolution considering precession). Therefore, there will be a leap month every three years to eliminate this extra 33 days!