Lunar calendar related:
In Eastern culture, the perpetual calendar and the lunar calendar can be said to be inseparable companions. When people check the perpetual calendar, they cannot do without lunar calendar information, such as auspicious days and inauspicious dates. It can be seen that in daily life, checking the perpetual calendar and the lunar calendar is almost equivalent!
Eternal Calendar in Western Countries
"Perpetual calendar", literally means "perpetual calendar", refers to the calendar used by foreigners. It is mainly used to confirm what day of the week a certain day in the past or future falls on. The current Gregorian calendar, which is the commonly used civil calendar, was promulgated by Pope Gregory XIII in 1582. But don't forget there is also the Julian calendar, which started being used during the reign of Julius Caesar. When the calendar was modified, October 4, 1582 (Julian calendar) was directly moved to October 15 (Gregorian calendar), making it 10 days earlier all at once!
Small Differences Between the Julian Calendar and the Gregorian Calendar
The biggest difference between the two is the rule for leap years. The Julian calendar has a leap year every four years, but the Gregorian calendar modified this: if the last two digits of the year are 00, it must also be divisible by 400 to be considered a leap year. This change was made to correct the problem of the Julian calendar: according to it, the average length of a year is slightly longer than a tropical year. Year after year, the small error accumulates, leading to a more serious discrepancy, which in turn prompted the modification of the calendar. The Gregorian calendar reduced the number of leap years, making the average number of days in a year closer to the time it takes for the Earth to complete one orbit around the Sun!
Definition and Use of the Perpetual Calendar
Whether it's the East or the West, the calendar of the perpetual calendar is very old. Although it's called "perpetual", it actually cannot check dates for ten thousand years; it's just a rhetorical device to emphasize that it can be used for a long time, usually for several hundred years. The perpetual calendar includes both the lunar calendar (yin calendar) and the solar calendar (yang calendar), as well as the Gan-Zhi calendar (Heavenly Stems and Earthly Branches)!
Origin of the Sexagenary Cycle
During the Shang Dynasty, people began to use the Heavenly Stems and Earthly Branches to record days. This is not a guess; there is evidence in the oracle bones excavated from the Yin ruins. On a piece of oracle bone, there is a sixty-stem-branch table, indicating that a method for recording days already existed at that time. By the Spring and Autumn and Warring States periods, the Heavenly Stems and Earthly Branches were also used in astronomy and time division, determining the twelve time periods. In the Han Dynasty, one day in the Taichu calendar was divided into twelve periods, using the Heavenly Stems and Earthly Branches to mark the time periods, and giving the time periods vivid and descriptive names, like 'midnight' and 'rooster crowing'!
Heavenly Stems and Earthly Branches are Stems and Branches
What to do in ten days? It's just Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, Gui; what about the twelve earthly branches? It's just Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai. Combine these two, and you can create sixty combinations, called the sixty Jiazi, used for counting years!
Lunar Calendar: A Combination of Yin and Yang Calendar
The lunar calendar is often mistakenly regarded as the yin calendar; in fact, it incorporates features of both the yin and yang calendars. The yin calendar records months and years based on the waxing and waning of the moon, while the yang calendar divides the year into twelve months according to the sun's trajectory, with two solar terms in each month. Ancient people compiled the combined lunar and solar calendar by observing celestial phenomena!
True Lunar Calendar
The lunar calendar, also known as the moon calendar, is based on the lunar cycle. A month averages 29.5306 days, and a year has only 354 days, which is 11 days shorter than the solar year. Therefore, it requires small and large months and leap months for adjustment!
Gregorian and Lunar Calendar
The current Gregorian calendar was jointly developed by scientists and mathematicians of the Roman era, and after multiple revisions and papal approvals, it formed the current version. The Gregorian calendar is based on the movement of the sun, so it is also called the solar calendar. The conversion between the Gregorian calendar and the lunar calendar is actually the conversion between the solar calendar and the lunar calendar!
Farmer's Calendar: Simplified Version of the Almanac
The Farmer's Almanac is a simplified version of the Tongsheng, which contains more information on auspicious and inauspicious dates, generally used by professionals; while the Farmer's Almanac is a simplified version for the general public. In the past, when the astrologers compiled the calendar, they would add some content to help people 'determine good and bad luck, and clarify trends and avoidance.' This type of book was originally called 'Tongshu,' and because 'shu' and 'shu' are homophones, it was renamed 'Tongsheng'!