Introduction to Chinese Calendar - How the astronomers developed it


What's a calendar?

A calendar is a system for measuring time, from hours and minutes, to months and days, and finally to years and centuries. The terms of hour, day, month, year and century are all units of time measurements of a calender system.

How does one measure time?

Distance can be measured with a stick. Time is measured by observing the movements of the sun, moon and stars. People in all major cultures have since discovered this fact since pre-historical time.

What's a 'Day?'

Every one knows about the rotation of the Earth about its axis, which causes (apparent) movement of the Sun from East to West across the sky. So we define one cycle of movement of the Sun as one 'Day.' The Chinese word is very straight forward and calls one day as one 'Sun.' More...

What's a 'Week?'

The concept of a "week" is less important in the Chinese calendar. The ancient Egyptians had a ten-day week, and so did the Chinese. The ancient Assyrians invented the seven-day week, and the names of days of the week that we use even today are based on a system of assigning the five planets visible to the naked eye, the sun, and the moon to the seven days of the week. More ...

What's a 'Month?'

For this we look at the Moon! Each night, the appearance of the Moon changes. From 'new moon' to 'full moon' and back. So we define a 'Month' as the time it takes for the Moon to go through one cycle of motion. As it happens, this takes about 29.5 days. So we round the month to be either 29 days or 30 days. Again, in the Chinese language a month is simply a 'Moon.' The English word "month" is derived from the word "moon." More...

What about a 'Year?'

The next larger unit of measurement of time is the 'Year.' For this we go back to the Sun again. Careful observations reveal that the over a period of many months (12), the position of the Sun shifts from very high overhead to a much lower point at Noon time. The length of daylight time also changes from longer to shorter. Even more importantly, the weather changes from hot to cold, giving rise to the four seasons of Winter, Spring, Summer and Fall. It is logical, therefore, to define the length of this time period as a 'Year.' The Chinese word for 'Year' is 'Nian', written as . Since the word 'Sun' has already assigned the meaning of a 'day', a new word has to be used to denote the 'year.'

How long is a year?

A little more than 365 days. In 104 B.C. the length of a year was determined to an accuracy of 365.2502 days. By 480 A.D., Ju Chongzhi refined it to 365.2428 days, or 52 seconds more than the modern value of 365.2422 days. To put it another way, in 2,000 years the total discrepancy is less than one day! Together with the voluminous annals of Chinese historians, the Chinese has provided the most accurate and uninterrupted time-line records.

Although 0.24 day does not look like much, over many years it becomes significant. How do we round it to a whole number of days? There are several different schemes to do this. The Chinese scheme is called the 'lunar calendar', and the nearly standard calendar is called the 'solar' calendar system.


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