Chapter 37 Section 2 Twelve Hours

During the Spring and Autumn Period and the Warring States Period, people began to apply the names of December in the calendar to astronomical directions.The basic assumption is that the sun moves on the ecliptic for one week in 12 months every year. If the ecliptic is divided into 12 corresponding sky zones, then one sky zone corresponds to one month.People call the sky area where the sun is located in winter solstice Zi, the sky area where the sun is located in December is called Chou, and so on.The revolution of the earth causes the annual movement of the sun from west to east on the ecliptic, and the diurnal rotation of the earth causes the day and night movement of the sun from east to west along the equator.Therefore, people assume that the orientation of the celestial equator is also divided into 12 sky zones, the north is the sub-position, the south is the meridian position, the east is the mao position, and the west is the unitary position. Then the sun travels 12 positions throughout the day and night to return to the original position. In this way, the concept that the sun is located at a position of a chen is an hour, and a day and night are 12 hours, and people can use the position of the sun in the sky to determine the time.

This method of timekeeping was probably produced after Emperor Wu of the Han Dynasty changed the calendar in the early days, and was first proposed by astronomers who participated in the calendar change at that time.This method is more scientific and concise, so it was quickly accepted by people, and the old timekeeping method was gradually abolished.This method of timekeeping first appeared in "Han Shu Yi Feng Chuan", which contains "Ri Jia Shen" in the first year of the Yuan Dynasty (48 BC), which means the moment when the sun is located in Shen.Since then, this method of timekeeping has appeared continuously, and the name of timekeeping has changed from "day plus afternoon" to "time plus afternoon", and then further simplified to "noon time".This timekeeping method corresponds to the 24-hour system as follows:

After entering the Wei, Jin, Southern and Northern Dynasties, science and technology have been further developed, and people have put forward higher requirements for the timekeeping system. Even in civil use, the twelve o'clock as an independent timekeeping system, the interval is too large Some.So people began to come up with some ways to improve it and divide it into more detailed ones. The first idea is to divide each hour into two, and insert the eight heavenly stems of A, B, C, D, Geng, Xin, Ren, and Gui and Gen, Xun, Kun, and Qian in the middle of the twelve hour names. Four hexagram names, a total of 24 hour names.This division has been used until the Sui Dynasty.This kind of time name is not very convenient to remember, and it does not seem to be so harmonious. Astronomers in the Tang Dynasty divided the twelve hours into two parts. It starts at 0 o'clock, noon starts at 11 o'clock, and noon starts at 12 o'clock.After making this improvement, the early 24-hour name was abolished.Dividing the twelve hours into two parts, the beginning and the beginning, is the twenty-four hour system in ancient China.It has been used until the Qing Dynasty.