What is a calendar?

The law of calculating the time length of year, month and day and the relationship between them, and making the time sequence is called calendar.

As early as in ancient times, people have gradually understood and mastered the movement law of the sun, the moon and the stars through long-term observation in production and life practice: from the phenomenon of alternating day and night, the concept of "day" has been formed; The concept of "moon" is formed according to the phase change of the moon and the movement period of the moon. From the phenomenon of alternating cycles of four seasons, the concept of "year" has been formed. The formation of these three concepts is independent of each other because of different objects. If the day with the longest sunshine in the four seasons is called the winter solstice, then the time between two consecutive winter solstice points is 1 year (1 tropical year); If the moon phase that appears after the new moon is called the new moon, then the time required for the new moon to appear again is 1 moon; The length of a day is well determined, that is, the sun is due south twice in a row, which makes the interval between sunshine and shadows the shortest. But the ancients discovered long ago that when the length of a day is determined, the length of a year is not an integer multiple of the day and the month, and the length of the month is not an integer multiple of the day. (According to modern accurate determination, the tropical year of 1 is 365.2422 flat solar days, that is, 12.3683 lunar month; 1 The first month of the lunar calendar is 29.5306 flat sun day. However, when making calendars, people are not used to dividing a complete day into two consecutive months or two consecutive years. Therefore, calendars formulated by countries all over the world are stipulated in different ways because of different customs and different emphases. We can generally divide them into three categories: one is the solar calendar, the number of days in a year is based on the astronomical phenomena, and the average is about the tropic of cancer, while the number of days in a month and the number of months in a year are artificially specified, such as the Gregorian calendar and julian calendar; The other is the lunar calendar, where the number of days in a month is artificially set according to the astronomical phenomena, such as the Islamic calendar and the Greek calendar. There is also a kind of lunar calendar, which calculates the year, month and day according to the astronomical phenomena. The average number of days in a month is about equal to the first month of the lunar calendar, and the average number of days in a year is about equal to the tropic year, such as the lunar calendar and Tibetan calendar still adopted in China.

In addition, the calendar also includes determining the beginning of a year, the beginning of a month, solar terms and time units longer than a year.

The original unit of time-the origin of the day

The first time unit that humans first knew was not a year, nor a month, but a day.

In the era of fishing and hunting in primitive society, nothing can affect human survival more than the brightness and warmth of dawn and the darkness and cold brought by sunset on the earth. The sun rises and sets in the west, and goes round and round. From this sunrise to the next sunrise, or from this sunset to the next sunset, such a natural time change cycle makes people gradually produce the concept of day.

With the concept of "day", people began to calculate the date. Counting dates is the need of the ancients to fight against nature, and it is also the logical development in the history of cognition. But at that time, under that condition, it was not easy to count the days.

As mentioned earlier, it is said that the ancients originally used the methods of "tying the rope to record the day" and "carving the wood to record the quotation" to calculate the day. These legends reflect the ancient people's intuitive counting of the initial sunrise and sunset, rather than speculation. Even today, similar traces can be found in the customs of some ethnic minorities (such as Dulong and Wa) in China.

The earliest method of recording Japanese in China was Oracle Bone Inscriptions's "Table of Branches and Branches" in the Yin and Shang Dynasties. Dry means that the sky is dry. It consists of 10 words "A, B, C, D, E, F, G, Xin, nonyl and decyl". Branches are earthly branches, represented by 12 words "Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai". Heaven is dry and earth is branched. It forms a pair of dry branches. If the heavenly stems begin with the word "A" and the earthly branches begin with the word "Zi", sixty pairs of stems and branches can be obtained by combining them in this order, which is called sixty Jia Zi or sixty Hua Jia. Choose one day as the beginning, and the days after that can be called the beginning. Although this method is simple, it appeared in the Yin Dynasty more than 3000 years ago, which is a great creation. According to historical records, China began on February 4th, the third year of Lu Yingong in the Spring and Autumn Period (722 BC), and lasted for more than 2,600 years (19 1 1) in Xuantong in the Qing Dynasty. This is the longest Japanese calendar record in the world.

Branches and branches were also used to track the moon, but they were soon abolished. Dating with dead branches began in the early years of the Eastern Han Dynasty and has never stopped since. Until today, for example, 1983, the words "the year of Guihai" are printed on the calendars of our country. In other words, AD 1983, the lunar calendar is the year of Guihai.

The origin of the month

The night sky is clear, the moon is high and clear as a mirror. The changeable moon, occupying the present, has aroused people's reverie and yearning! The Goddess Chang'e flying to the moon is a masterpiece through the ages. "Lonely Chang 'e Twilight Sleeve, Wan Li in the sky, dancing for the loyal soul. "This immortal poem, a more beautiful myth, shines with brilliance.

The moon is the most remarkable astronomical phenomenon in the night sky. In ancient times when there were no lights and candles, fishing, grazing and even some farm work could be done in the moonlight. Even in the era when fire can be used for lighting, the moon still has a great influence on people. "Things always follow the moon, and when you attack and fight, you will retreat when you are defeated in the moon" (The Story of Xiongnu in Hanshu), and even you have to use moonlight to March and fight. So for the ancients, the role of the moon was second only to that of the sun.

Chang's "twelve out of ten" is probably the earliest understanding of the moon by the ancients. They think that the moon will slowly die from the full moon, and a new moon will come out next month. But, "What is the virtue of glowing? Death is fruitful "(Qu Yuan: Tian Wen) reflects the ancients' further thinking about the moon.

The rise and fall of the moon, as well as the change of its roundness and wane, is one of the earliest astronomical phenomena recognized by human beings. The bronze inscriptions of the Zhou Dynasty in China began with the appearance of the "rib"-the new moon on the third day, which was called "the first auspicious day". Pushing forward from the "rib", on the first and thirtieth day of each month, there is no moon at all. This is the "new moon". Around the tenth five-year plan, the moon is the roundest, called "Wang". People noticed that the change of Wang Shuo had a fairly accurate cycle, which gave birth to the concept of Wang Shuo's moon.

The so-called new moon is to set the time interval from this new moon to the next, or from this time to the next time interval as January, which is equal to 29 ~ 30 days.

The appearance of the new moon is another time period after the "sun". The development from the initial time unit "day" to a longer time unit "month" marks a step forward in human understanding and measurement of time.

Now we know that the moon is a satellite of the earth. It goes around the earth, and it doesn't shine, but reflects sunlight. In the process of the earth and the moon orbiting the sun together, sometimes sunlight can completely illuminate the surface of the moon facing the earth, sometimes it can only partially illuminate, and sometimes it can't illuminate at all. So people living on the earth will see that the moon has different shapes, called the moon phase, also called profit and loss.

The phase change of the moon mainly has five stages: the first quarter of the new moon, the first quarter of the full moon and the last moon. On the evening of the second and third day of the lunar calendar, the new moon appears in the west of the sky, which is the "rib" mentioned above. The first quarter moon appears on the eighth and ninth days, and you can see half the moon. The full moon is on the 15th and 16th, when the sun and the moon are just opposite each other across the earth, so it is also called "looking". The last quarter moon is a crescent moon that appeared in the east of the sky in the early morning of 2067. On the first and thirtieth day of each month, the side of the moon facing away from the earth just faces away from the sun, which is the "new moon" mentioned above.

How many days does a new moon contain? This is not a simple number. Because the orbit of the moon around the earth is an ellipse. When the moon moves in an elliptical orbit, one of the points is closest to the earth, which is called perigee; The farthest point from the earth is called apogee. Near perigee, the moon moves faster; Near apogee, the moon moves slowly. So the speed of the moon is not uniform, but changes periodically. In addition, the apparent motion of the sun changes periodically, so the time of the moon's absence is not fixed. Modern observation shows that the exact length of the first lunar month is about 29.5306 days. Please remember this number, which is the reason and basis for the division of large and small months in the lunar calendar.

The origin of a year

In people's modern life, a long time interval, such as recalling the past or planning the future, is often based on "years". We are used to Nian today. But it took thousands of years in the history of science to understand this cycle and organize it into applicable time units!

Although historians of science can't explain exactly when the concept of year came into being, one thing is certain, that is, it must have appeared with the development of agricultural society. Millet stored in Xi 'an Banpo site, Chinese cabbage and mustard seeds stored in clay pots; There are a lot of rice in Hemudu site in Yuyao, Zhejiang Province, which shows that there was a certain level of agriculture on the vast land from the Yellow River basin to the south of the Yangtze River as early as 6000 years ago. It should be admitted that people had basically mastered the relationship between the basic laws of the four seasons and the growth cycle of crops. Because the development of agriculture depends on grasping the season from the beginning.

Of course, we don't mean that people in that era have learned to observe astronomical phenomena and master their changing laws. The alternation of years is the cycle of the earth revolving around the sun. At that time (about the Neolithic Age), there was not only the scientific level of observing the laws of celestial bodies, but also the concept that the earth revolved around the sun. The ground motion theory was put forward by Copernicus, a modern Polish astronomer, in the17th century.

Therefore, we can think that the year of primitive human understanding was not based on astronomical phenomena at first, but on various natural phenomena on the earth: river flooding, vegetation withering, bird and beast migration, alternating cold and warm, and so on. Even today, some farmers judge the seasons according to these natural phenomena, and the difference will not be too big. These natural phenomena are collectively called "phenology".

The working people in ancient China have accumulated a lot of experience in observing phenology in their long-term production activities. In the ancient book "Summer", there was a rich description of phenology, one of which said:

In the first month, geese fly north, fish float, voles come out of holes, and peach trees bloom;

In February, millet was planted, lambs gave birth to lambs, violas sprouted, and insects were ready to move;

In March, mulberry leaves germinate and willow trees sprout;

In April, apricot trees bear fruit and frogs croak in the fields of Gouhe River.

In May, cuckoos crow, cicadas sing and summer melons bear fruit;

In June, peaches are ripe and eagles learn to fly;

In July, the rainy season comes and reeds grow;

In August, the melons are ripe and the dates are coming down.

In September, geese move south, chrysanthemums are in full bloom, and birds and animals are preparing for winter;

In October, crows fly around, ready to hunt;

1 1 month, the antlers went bald and started hunting;

In December, insects dive underground and kites fly in the sky. ...

There are many records about phenology in ancient China, and almost every nation has its own Xia Zhengxiao. These phenological observations were initially purely intuitive. However, on the basis of a large number of intuitive observations, the ancients will inevitably begin to think about the changing laws of these phenology, thus gradually forming the concept of year.

Of course, different nationalities have different phenological phenomena based on different living environments and different observation objects. For example, when describing the extension of the customs of the Qiang people in Wei Shu, he said: "The customs are silent, and the years will not be remembered until the vegetation flourishes and withers." In ancient China, Nian had different names (even in modern times). Er Ya Shi Tian explains the year: "Summer is old, business is called worship, Zhou is called year, and Tang Yu is called load." In Wei Shu, it is said that "vegetation records years", that is, records years.

In addition, the ancient Mongolians who lived on the grasslands in northern China simply took pasture as the year. They call a few years old "how many grasses" or "how green the grass is".

In ancient times, phenological observation was generally rough, coupled with climate change, so even in the same area, phenological phenomena would vary from time to time, which could not meet the needs of the development of agriculture and animal husbandry, which prompted the ancients to slowly learn to use astronomical phenomena to change the chronology.

Division of four seasons

After understanding the "year", the ancients subdivided the "year" in labor practice. Divided into two, divided into four, resulting in four seasons.

We now call spring, summer, autumn and winter the four seasons, and the ancients called them the four seasons. The early division of the four seasons is artificial. Warm spring, hot summer, cool autumn and cold winter are different in different areas. In some parts of the world, there are two seasons: dry season and rainy season; Some places are divided into three seasons: rainy season, cold season and hot season; Some places even have six seasons. But the names of spring, summer, autumn and winter are widely used all over the world.

The division of the four seasons in ancient China originated from the "Four Sides". The article Guanzi Four Seasons has this explanation:

The stars are in the east. It was spring then.

It's sunny in the south, but it's summer.

To the west, it was Chen. It was autumn.

The moon is in the north. It was winter then.

In foreign countries, ancient Greece was the first country to divide the year into four parts. The ancient Greeks divided a year into four seasons: spring, summer, autumn and winter, marked by the rise and fall of the Pleiades and arcturus.

With the development of astronomy, it took many centuries before people gradually linked the four seasons with the annual apparent motion of the sun.

As we know, the sun is a star and the earth revolves around it. The movement of the earth consists of two parts, one is rotation and the other is revolution. A turn is a day, and a turn is a year. We live on the earth and can't detect the movement of the earth. Look at the stars in air movement at night and the sun in air movement during the day. Astronomy calls this seemingly moving phenomenon apparent motion.

If you carefully observe the apparent motion of the sun, you will find that the sun not only rises and sets every day, but also moves on the background of stars. After a certain period of time, this movement makes the sun revolve around itself in the stars, and then returns to its original starting position. Reflected in the celestial sphere, the sun draws a big circle on the celestial sphere. This great circle is called the ecliptic. The ecliptic and equator intersect at two points on the celestial sphere, one is called vernal equinox and the other is called autumnal equinox. On the ecliptic, there are two points opposite to the vernal equinox and the autumnal equinox, namely, the summer solstice and the winter solstice. The movement of the sun on the ecliptic is called the annual apparent movement of the sun. If spring is the starting point, the time when the sun orbits the ecliptic and returns to the vernal equinox is a tropic year.

When the sun runs on the ecliptic, it enters the northern hemisphere from the southern hemisphere of the celestial sphere through vernal equinox on March 2 1 every year. At this time, the time of day and night on the earth is equal. On June 2 1 day, the sun reached the summer solstice. At this time, the sun in the northern hemisphere has the highest height and the longest day. Around September 23rd, the sun entered the southern hemisphere from the northern hemisphere of the celestial sphere through vernal equinox, and the time of day and night on the earth was equal again. Around February 22, 65438, the sun reached the winter solstice, with the lowest sun height and the shortest day in the northern hemisphere. The four seasons on the earth, from spring and summer to autumn and winter, from summer to cold, are endless, which is caused by the annual visual movement of the sun.

The equinox (vernal equinox and autumnal equinox) and the solstice (summer solstice and winter solstice) are the midpoint of each season. The midpoint from the winter solstice to the vernal equinox is beginning of spring, which is called "beginning of spring". Other seasons, etc.

The significance of studying calendar

Due to the needs of production and life, as early as ancient times, people were eager to understand and master the changing laws of day and night, moon phases and seasons, as well as longer-term measurement methods. Ancient civilizations in the world began to make calendars based on astronomical observations very early. Now we know that there are sidereal day, True Sun Day and Peaceful Sun Day, Stellar Moon and Lunar Moon, Stellar Year and Tropic Year.

Which year, month and day should we choose as the standard in the calendar?

Ancient people used the true solar day as the length of the "day", but the true solar day was long and short, which was not suitable as a unit for calculating time. Although sidereal day is relatively unified, it has little to do with people's lives. People's daily life is closely related to the appearance of the sun and the alternation of day and night. As people often say, "work at sunrise and rest at sunset" reflects human dependence on the sun. However, the beginning of sidereal day is uncertain, starting at noon on the day of the vernal equinox and starting at midnight on the day of the autumnal equinox. So people summed up and imagined a flat solar day, which is the basic unit of time that we still use today. Although we now know that the sidereal moon is the real cycle of the moon's revolution around the earth, it has nothing to do with our daily life. It has attracted people's close attention to the moon since ancient times. The moon's profit and loss is not only remarkable, but also closely related to human nighttime activities and tidal changes, so it naturally becomes a longer time unit than the sun. For a unit of time longer than a month, I'm afraid we can't ignore the periodic changes of the four seasons. The planting and harvesting of crops are closely related to human life, and the corresponding year can only be the year of the return of the sun, not the year of the sidereal. Because the days, months and years used in calendars are not completely equal to the real solar days, new moons and tropical years, we call them "calendar days", "calendar months" and "calendar years".

The standard length unit of time has been determined, which only needs further precision. However, it is still difficult to make a calendar: how to make every day different from any other date in order to record the order of events; How to predict the coming of hot and cold weather and the change of the moon phase according to the calendar ... The most difficult thing here is probably to specify the number of months of 1 and the number of days of 1, because there is no greatest common denominator among days, months and years, the tropical year of 1 is 365.2422 flat solar days, and the lunar month of 1 is 20. How to make the length of years in the compiled calendar equal to the tropic year and the length of months equal to the first month of the lunar calendar, which is both convenient to use and easy to remember ... These requirements cannot be met at the same time, but if they are not handled properly, the consistency of months and seasons, dates and moon phases will inevitably be destroyed over time. It may snow in February this year and rain in a few years; August 15 this year is the Mid-Autumn Festival. After a while, the first day of August and January may be full ... using this hot and cold reversed calendar has brought great inconvenience to our lives. Therefore, how to make proper adjustments and arrangements according to the actual relationship between day, month and year, so that the daily order can not only conform to the rhythm of natural phenomena, but also adapt to the laws of human life, and be as neat, simple, easy to remember and easy to use as possible, is indeed a science.

The Gregorian calendar, which is widely used in most countries in the world today, is undoubtedly in an advanced position compared with the old calendars of various countries in history. However, there are still many unsatisfactory aspects in the solar calendar. For example, the number of days in each month is different, and there are too many leap days (there is a leap day every four years, and there are 97 leap days in 400 years), which makes it difficult to calculate the past and future dates. In the past 100 years, many scientists in the world have been exploring ways to change calendars. 19 10, a "World Calendar Change Conference" was held in London. Up to now, there have been more than 100 schemes to change the calendar, but still no new calendar is recognized as the most scientific and practical. It is so difficult to change the calendar because the calendar is strictly constrained by the operation of astronomical phenomena. At present, the newly calculated tropical year is 365.438+09879 flat solar day. Although the mantissa after the decimal point puzzles many scientists, perhaps another new calendar scheme that is easier to calculate and remember and will not be out of step after tens of thousands of years is quietly taking shape.