When are the twenty-four solar terms in China lunar calendar? How did it come from?

Solar terms are precious scientific heritages created by Chinese ancestors after thousands of years' practice, and they are tools to reflect the changes of weather, climate and phenology and master the farming season.

As early as the Spring and Autumn Period and the Warring States Period, China was able to measure the length of the sun's shadow at noon with a soil gauge (a pole was erected on the plane), thus determining four solar terms: winter solstice, summer solstice, vernal equinox and autumn equinox. In a year, the shortest day of the noon soil return shadow is the summer solstice, the longest day is the winter solstice, and the shadow with moderate length is the vernal equinox or autumn equinox. The Book of History in the Spring and Autumn Period recorded the solar terms. The twenty-four solar terms are completely recorded in Huainanzi written by Liu An in the Western Han Dynasty. In ancient China, the lunar calendar was used to record time, and the solar calendar was used to divide the 24 solar terms of spring, summer, autumn and winter. Our ancestors called five days 1, and three days were called solar terms. The whole year was divided into 72 days out of 24 solar terms.

With continuous observation, analysis and summary, the division of solar terms is gradually enriched and scientific. By the Qin and Han dynasties more than 2000 years ago, a complete concept of 24 solar terms had been formed.

In ancient times, a year was divided into twelve months, and each month had two solar terms. The former is solar terms, while the latter is neutral. For example, beginning of spring is the first month's festival, and it rains in the first month. Later generations called solar terms and neutral gas solar terms.

The names of the 24 solar terms are: beginning of spring, Rain, Sting, Vernal Equinox, Qingming, Grain Rain, Changxia, Xiaoman, Mangzhong, Summer Solstice, Xiaoshu, beginning of autumn, Chushu, Bailu, Autumnal Equinox, Cold Dew, Chufrost, beginning of winter, Light Snow, Winter Solstice, Slight Cold and Severe Cold.

The twenty-four solar terms are divided according to the position of the sun on the ecliptic (that is, the orbit of the earth around the sun). Depending on the sun starting from the vernal equinox (longitude zero, at this moment the sun shines vertically on the equator), every advance of 15 degrees is a solar term; After a week's operation, I returned to the vernal equinox, which is a tropical year with 360 degrees, so it is divided into 24 solar terms. The dates of solar terms are relatively fixed in the solar calendar. For example, beginning of spring in the solar calendar always falls between February 3rd and 5th. However, in the lunar calendar, the date of solar terms is not easy to determine. Take beginning of spring as an example. It can be the first day of the lunar calendar in the previous year, 65438+February 15, and the latest is the first month, 15.

It can be seen from the naming of the twenty-four solar terms that the division of solar terms fully considers the changes of natural phenomena such as seasons, climate and phenology. Among them, beginning of spring, Changxia, beginning of autumn, beginning of winter, vernal equinox, autumnal equinox, summer solstice and winter solstice are used to reflect the seasons, and a year is divided into four seasons: spring, summer, autumn and winter. The vernal equinox, autumnal equinox, summer solstice and winter solstice are divided from an astronomical point of view, reflecting the turning point of solar height change. Beginning of spring, Changchun, beginning of autumn and beginning of winter reflect the beginning of the four seasons. Because China is a vast country with a very obvious monsoon and continental climate, the weather and climate vary greatly from place to place, so the four seasons in different regions are also very different.

The five solar terms of slight summer heat, great summer heat, slight cold and severe cold reflect the change of temperature and are used to express the degree of heat and cold in different periods of the year; Rain, Grain Rain, light snow and heavy snow reflect the phenomenon of precipitation, indicating the time and intensity of rainfall and snowfall; The three solar terms, White Dew, Cold Dew and First Frost, on the surface reflect the phenomenon of condensation and condensation of water vapor, but in essence reflect the process and degree of gradual temperature drop: when the temperature drops to a certain extent, water vapor condenses; The continuous drop in temperature not only increases condensation, but also gets colder and colder; When the temperature drops below zero degrees Celsius, water vapor condenses into frost.

Xiaoman and awn seeds reflect the maturity and harvest of related crops; Frightening and Qingming reflect natural phenology, especially stinging, which indicates that spring will return with the recovery of early thunder in the sky and underground stinging insects.

The comparison list of dates between 24 solar terms and Gregorian calendar is as follows:

Solar Term Month Day Solar Term Month Day Solar Term Month Day

Slight cold 65438+1October 5 or 6, long summer May 6 or 7, September 8 or 9 of the Millennium.

Great cold on 20th or 2 1, autumnal equinox on 2nd1or 22nd, 23rd or 24th.

Beginning of spring February 4th or 5th, June 6th or 7th, cold dew 65438+1October 8th or 9th.

Rain 19 or 20 summer solstice 2/kloc-0 or 22 first frost 23 or 24.

On March 6th and 7th, I was in a daze, and on July 8th, it was slightly hot. beginning of winter165438+1October 7th and 8th.

Vernal equinox 2 1 or 22, intense heat 23 or 24, light snow 22 or 23.

On April 5th and 6th in Qingming Festival, August 8th and 9th in beginning of autumn, with heavy snow of 65438+ February 7th and 8th.

Grain Rain 20th or 2nd1Summer, 23rd or 24th Winter Solstice, 23rd or 24th.

Introduction to the 24 solar terms (1)

Beginning of Spring

Since the Qin Dynasty, beginning of spring has been the beginning of spring in China. Beginning of spring is divided from astronomy, but in nature and people's minds, spring is warm and flowers are fragrant. Spring is growth, cultivation and sowing. In climatology, spring refers to the period when the average temperature is between 10℃ and 22℃. Speaking of beginning of spring, people obviously feel that the days are getting longer and the sun is getting warmer. Temperature, sunshine and rainfall are often at the turning point of the year and tend to rise or increase. The growth of crops in early spring is accelerated, and the water consumption for bolting rape and jointing wheat is increased. Irrigation and topdressing should be done in time to promote growth. Agricultural proverbs remind people: "When it begins to rain in spring, get up early and go to bed late." Da Chun also began to prepare for farming. Although "spring" has been established, frost will still appear in most areas of the basin. In a few years, there will be a scene of "snow can't reach spring, so it flies through trees". These climatic characteristics should be taken into account when arranging agricultural production. Where is the information that people often look for in spring? The buds protruding from the wicker are "softer than gold and softer than silk"; The eager grass in the soil is waiting for "they grow taller in the spring breeze"; In order to win a new harvest, people who work hard in the fields are creating real spring with their hands.

Rain Water

The rainy season means that it begins to rain and the rainfall gradually increases. In the Yellow River valley, the birthplace of the 24 solar terms, it was cold before the rain, but it was snowing and raining unpleasantly. After the rain, the temperature can generally rise above 0℃, with less snow and more rain. However, in the warm climate of Sichuan Basin, even in the dead of winter, rainfall is not uncommon. During this period, the average climate temperature in our province is mostly above 10℃, peaches and plums are in bud, and cherries are in full bloom. It is indeed a climatic spring. In addition to a few years, the frost period has come to an end. Grafting fruit trees and planting trees is just the right time. After the dry winter, there are many droughts in spring all the year round, especially in the west of the basin. In agriculture, attention should be paid to moisture conservation and timely irrigation to meet the water supply at jointing and booting stage of wheat and at the critical stage of bolting and flowering of rape. The mountainous area of western Sichuan Plateau is still in the dry season, with low temperature and high wind speed, which is prone to forest fires. In addition, the invasion of cold wave will cause strong cooling and snowstorm, which will do great harm to the old, weak and young animals. These should pay special attention to prevention. Time flies and the seasons remind people. "A year's plan lies in spring". The management of Koharu and the preparations for Da Chun should be carried out quickly, so as to make this year better than previous years.

Awakening of Insects

Sting, which reflects the natural phenological phenomenon, refers to the sudden movement of spring thunder, which wakes up the hibernating animals in the soil. At this time, the temperature rose rapidly, and spring thunder gradually appeared in most areas of the Yangtze River Basin. In the eastern part of the basin of our province and the southern part of Liangshan Prefecture, the first sound of spring thunder can also be heard in the perennial rain and stormy waves; In the northwest of the basin, except for a few years, it usually doesn't thunder until Qingming, which is the latest area where thunderstorms begin in our province. By the time of the earthquake, most parts of China had entered the busy season of spring ploughing. Really: the season waits for no one, and every moment is worth a thousand dollars.

Spring Equinox

The vernal equinox is one of the solar terms reflecting the changes of the four seasons. In ancient China, beginning of spring, Changxia, beginning of autumn and beginning of winter were used to indicate the beginning of the four seasons. The vernal equinox, summer solstice, autumn equinox and winter solstice are in the middle of each season. On the vernal equinox, the sun shines directly on the equator, and the time between day and night is equal all over the earth. Therefore, the ancient vernal equinox and autumnal equinox are also called "equinox", and there is a folk proverb that "vernal equinox and autumnal equinox are equally divided day and night". After the vernal equinox, the overwintering crops in most parts of China entered the spring growth stage. There is an agricultural proverb in Central China, "Wheat starts at the vernal equinox, and every moment is worth a thousand dollars".

Qingming Festival

Qingming is a solar term representing phenology, which means sunny weather and lush vegetation. Tomb-Sweeping Day has folk customs such as climbing mountains, eating cold food and sweeping graves. As the saying goes, "Qingming breaks snow, Grain Rain breaks frost." When the weather is clear, the climate in the basin is warm and the spring is strong. However, before and after Tomb-Sweeping Day, cold air still invaded from time to time, even making the average daily temperature lower than 12℃ for more than three consecutive days, resulting in rotten seedlings of middle rice and dead seedlings of early rice. Therefore, it is necessary to avoid warm tail and cold head when sowing and transplanting rice.

Grain Rain

As the saying goes, "Rain gives birth to a hundred valleys". With sufficient and timely rainfall, cereal crops can thrive. Grain Rain solar terms have such a meaning. It is the sixth solar term among the 24 solar terms and the last solar term in spring. As the saying goes, "It's snowy in Qingming Festival and frosty in Grain Rain", and the average temperature in most parts of the country is above 12 degrees. After Grain Rain, the temperature rose rapidly, and from that day on, the rainfall began to increase. Abundant rainfall has irrigated and moistened the newly planted seedlings and new crops, and the grain is growing well. The duckweed in the pond began to breed, and the mulberry trees also grew new green leaves. This is the time when sericulture families began to be busy. At this time, spring tea also began to harvest around this time. In the south of the Yangtze River, from hills to mountains, sweaty tea farmers are busy picking tea, and tea farmers are busy making tea at home. The fragrant tea fragrance permeates the countryside of Shan Ye. After Grain Rain, agricultural production entered a busy period. Therefore, it is very important to seize the opportunity after the autumn harvest, intensively cultivate, pay attention to the weather changes, compete for seeds and plants, and not miss the farming season.

Early summer

As the name implies, long summer refers to the beginning of summer. However, the temperature varies from place to place, and the time of entering summer is actually inconsistent. According to climatology, the five-day average temperature is higher than 22℃ as the standard in summer. The sixth day of the fifth lunar month is a long summer. At this time, "Dou refers to the southeast, Wei is the long summer, and everything has grown up since then, so it is named long summer." At this time, the longitude of the sun is 45 degrees. Astronomically, Chang Xia said that bidding farewell to spring is the beginning of a summer. When the temperature rises obviously, the summer heat comes, thunderstorms increase and crops enter the peak season, people are used to taking long summer as an important solar term. After the long summer, it is the key period for planting early rice in a large area, and the arrival and amount of rain during this period are closely related to the future harvest. The farmer's proverb says well: "If it doesn't last long in summer, the plow will hang high." "There is no rain in the long summer, and there is no rice in the head." There is also a folk custom, saying that weight is afraid of summer heat. It is said that after weighing this day, you will not be afraid of the heat and lose weight, otherwise you will be troubled by the disease. Jiangxi also has the custom of drinking tea in the long summer, saying that if you don't drink tea in the long summer, you will suffer all summer. As early as ancient times, kings often went out of the city to welcome summer on the first day of summer, and the day to welcome summer was long summer.

Introduction to the Twenty-four Solar Terms (2)

Grain Buds

Most of the 24 solar terms can be defined by their names, but Xiaoman is somewhat puzzling. Originally, Xiaoman means that summer crops such as wheat are full of milk and seeds. Agricultural proverbs in Sichuan basin give Xiaoman a new meaning: "Xiaoman is not satisfied, he thinks about it"; "Little people are full of discontent, regardless of mangoes." The word "full" is used to describe the amount of rain, and it is pointed out that if there is not enough water in the field when it is full, the ridge may crack and even rice cannot be planted when it is planted. Because "transplanting rice in long summer and planting rice in small fields" and "seedlings rushing into small fields in autumn", small fields are suitable for rice planting. The severity of summer drought in the basin is directly related to the rice planting area. Planting sooner or later is closely related to the yield of rice. In the central and western parts of the basin, there are often droughts in winter and spring, and heavy rains come late. In some years, the rainstorm didn't come until June, or even as late as July. In addition, the annual rainfall in the small solar term is not much, with an average of only about 40 mm, and the natural rainfall can not meet the water demand for planting seedlings, which makes the summer drought in the central part of the water-deficient basin more serious. As the saying goes, "storing water is like storing grain" and "preserving water is like storing grain". In order to resist drought, in addition to improving cultivation measures and speeding up afforestation, it is especially necessary to pay attention to water storage and moisture conservation in the first year. However, we should also pay attention to the possible continuous rainy weather, which will affect the harvest and drying of spring sowing crops. In the mountainous area of western Sichuan Plateau, at this time, many crops have entered the rainy season, and the crops are growing vigorously and thriving.

Grain in Ear

The awn seed is a symbol of the maturity of awned crops such as wheat and a solar term reflecting agricultural phenology. By the time of the awning, the wheat harvest season in Sichuan Basin has passed, and the transplanting of mid-season rice and sweet potato is coming to an end. In most areas, the mid-season rice has entered the green stage, and the seedlings are green and full of vitality. The poem "The east wind dyed 3,000 hectares, and the herons kept coming and going" vividly described the beautiful scenery of the field at this time. In the awning season, the medium rice that has not been transplanted in the basin should be planted quickly; If it is postponed again, the vegetative growth period of rice will be shortened due to the increase of temperature, and the growth period will be easily affected by drought and diseases and insect pests, and the yield will inevitably be low. Osmunda japonica should be transplanted before summer at the latest; If sowing is too late, not only the drought will worsen, but also the temperature will drop in Qiu Lai, which is not conducive to the expansion of potato chips and the yield will be significantly reduced. This is the truth of the agricultural proverb "busy planting".

Summer solstice

On the solstice of summer, the sun shines directly on the Tropic of Cancer, which is the longest day of the year in the northern hemisphere. It takes about fourteen hours from sunrise to sunset in all parts of Sichuan. Although the summer solstice has the longest day and the highest sun height, it is not the hottest time of the year. Because the heat in the near-surface layer is still accumulating at this time, and it has not reached its maximum. After the summer solstice, due to the vigorous growth of crops, the rapid growth and spread of weeds, pests and diseases, and the golden season of grass, fertilizer and livestock flourishing in plateau pastoral areas, agricultural production in our province has entered the field management period. At this time, the rainfall in the western part of the basin increased obviously, which gradually changed the distribution trend of rainfall in the basin from the east to the east since the spring. If there is a summer drought, it is generally expected to be lifted at this time. In recent 30 years, the number of large-scale floods in the western part of the basin in late June is small, but the degree is serious. Therefore, special attention should be paid to preparing for flood control. The solar term from summer solstice is the solar term with the largest annual rainfall in the eastern part of the basin, which is often controlled by subtropical high in the future, resulting in summer drought. In order to enhance drought resistance and win a bumper harvest in agriculture, it is an important measure to capture and store pre-dormant rainwater in these areas. After the summer solstice, the ground is heated strongly and the air convection is strong, and thunderstorms are often easy to form in the afternoon to evening. This kind of hot thunderstorm comes and goes, and the rainfall range is small. People call it "dividing fields in summer and rain". In Sichuan, Liu Yuxi, a poet of the Tang Dynasty, skillfully used this weather to write a famous poem "Rising in the east and descending in the west, the road is sunny and sunny".

Minor Heat

Trees are shady and summer is hot. The average summer temperature in Sichuan Basin is about 26℃, which is already midsummer and quite hot, but it is not the hottest time yet. In mid-July, in the low-altitude valley area in the southeast of the basin, there may be a concentrated period in which the daily average temperature is higher than 30℃ and the daily maximum temperature is higher than 35℃, which is unfavorable for heading and flowering of hybrid rice. In addition to fully considering this factor in the layout in advance, corresponding remedial measures should be taken for those that have been planted. In the northern Sichuan Plateau, frost and snow can still be seen at this time, which is equivalent to the scene of early spring in the basin. Around the summer, the western part of the basin enters the season with the most rainstorm, and the number of rainstorm days in July and August can account for more than 75% of the whole year, usually about 3 days. Mountain torrents often occur in places with large relief, and even cause mudslides. However, in the eastern part of the basin, due to the frequent control of subtropical high, the weather is sunny and hot, and after experiencing a slight summer heat, it began to enter the summer drought period. The climatic characteristics of the waterlogging in the east and west of this basin in our province are closely related to the abundance and shortage of agriculture. We must take drought and flood control measures as soon as possible to minimize the harm. Around the summer heat, all parts of our province entered the season with the most thunderstorms. Thunderstorm is a disastrous weather phenomenon, often accompanied by strong winds, heavy rain and sometimes hail, which is easy to cause disasters and must be prevented.

Major Heat

Hot in summer means hot. Explanation is the hottest solar term in a year. Generally speaking, the summer solar term is the period with the most sunshine and the highest temperature in a year in the basin, the period with the most abundant rainfall, the most common thunderstorm and the most concentrated high temperature days above 30℃ in the west of the basin, and the period with the most frequent high temperature above 35℃ in the east of the basin. The high temperature around summer is a sign of normal climate, because in Da Chun, higher temperature is beneficial to the flowering and filling of crops. However, if the temperature is too high, it will inhibit the growth of crops and the seed setting rate of rice will decrease obviously. After the western part of the basin was flooded, light, heat and water were at the peak of a year, which promoted each other and formed good climatic conditions for crop growth in Da Chun, but attention should be paid to flood control and drainage. In the eastern part of the basin, high temperature and long sunshine are often accompanied by little rain, which will not only limit the exertion of light and heat advantages, but also aggravate the adverse effects of drought on crops in spring and summer. In order to resist summer drought, we should not only pay attention to early water storage, but also improve crop cultivation measures based on "early" according to the climatic characteristics in the eastern part of the basin, so as to achieve advantages and avoid disadvantages. The sultry summer is the season when jasmine and lotus are in full bloom. The more fragrant jasmine is, the more fragrant it is, giving people a clean and fragrant enjoyment. Noble lotus flowers, not afraid of the hot sun and showers, gather in the morning and evening. The poet praised it as "reflecting the different colors of lotus flowers in the sun", and the vibrant midsummer is gestating a bumper harvest.

Introduction to the Twenty-four Solar Terms (3)

Beginning of Autumn

"It's cool on beginning of autumn Day" obviously associates beginning of autumn with cool weather. It can be seen that beginning of autumn is the beginning of cool autumn. Because of the different latitudes and altitudes, it is practically impossible to enter autumn at the same time in beginning of autumn. According to the climatological standard that the five-day average temperature is between 10℃ and 22℃, in China, except those places with high altitude in north latitude, beginning of autumn is still in hot summer, and even in most parts of Northeast China, there is no autumn scenery with cool breeze and yellow leaves fluttering. For the Sichuan Basin located in the middle subtropical zone, the summer heat is still heavy in August all the year round. Statistics of climate data show that the basin will not enter autumn until the middle and late September. It is impossible to say when autumn begins in the plateau mountainous area where winter is all the year round or winter is long without summer, and spring and autumn are connected.

The heat is over

Summer is a solar term reflecting the temperature change. "Chu" means to hide and die, and "early summer" means that the hot summer has passed. The Twelve Episodes of the Moon Order says: "In mid-July, this place will stop, and the summer heat will stop here." At this time, the dog days have passed or will soon end, so it is called "the summer ends here". There are also proverbs all over the country, indicating that the summer heat is fading away. However, the weather in autumn is not really cool. At this time, the sunny afternoon is no less hot than midsummer, which is in line with the saying that "autumn tigers are as poisonous as tigers". This also reminds people that there will still be hot weather in autumn, which can be regarded as a return of summer. Gu Tieqing, the author of Jia Qinglu, described the summer heat: "After the summer heat, the weather is still gloomy, and it will take about 18 days to cool down;" As the saying goes, eighteen pots of summer heat means eighteen days of bathing. "This means about eighteen days of sweating. At this time, the longitude of the sun is 150 degrees, and the almanac records: "Fighting refers to the summer heat, and the summer heat will retreat, crouching and diving, hence the name. "

From the agricultural point of view, there is also the autumn harvest scene of "summer valley yellow" and "busy rice fields". In addition, after the summer, continuous autumn rains often patronize us. Farmers should pay special attention to the weather forecast, seize every sunny day, and do a good job in autumn harvest without losing time.

White Dew

Dew is water droplets formed by condensation of water vapor on the ground or near-earth objects due to temperature drop. So the Millennium actually indicates that the weather is getting cold. September 7th to 9th in the solar calendar is the millennium. Millennium is a typical autumn solar term. From this day on, dewdrops became more and more dignified and famous. According to the lunar calendar, "the bucket refers to the dew, and the yin is getting heavier and heavier, so it is called dew." The longitude of the sun at this time is 165 degrees. Because of the cold weather, the water vapor in the air often condenses into dew on trees and flowers every night, and birds begin to prepare for winter. "Book of Rites and Moon Order" records the scene of this solar term: "When the blind wind comes, the geese come, the mysterious birds return, and the birds are ashamed." In other words, this solar term happens to be the time when geese fly south to avoid the cold and birds begin to store dried fruit food for the winter. It can be seen that the Millennium is actually a symbol of cold weather.

Both of them are Millennium solar terms, and their scenery is different in different parts of China. The water vapor in the north is condensed, and some areas in the south are still full of flowers. There was a saying that "after a thousand years, osmanthus fragrance". There is also a saying that the Millennium solar terms shelter from the wind and rain, such as "the northeast wind of the Millennium, ten bells (cotton peaches) and nine pus; It's windy in the northwest, ten rings and nine empty "and so on. From this proverb, it is not difficult to see that farmers' friends attach importance to solar terms.

Autumn Equinox

The autumnal equinox is a solar term representing seasonal changes. On the day of the autumnal equinox, the sun is located at longitude 180 degrees, and the sunlight is almost direct to the equator, and day and night are almost equal. "The bucket refers to the autumnal equinox, and the northern and southern hemispheres are equally divided day and night, which is half autumn, hence the name." The longitude of the sun is 180 degrees, and the solar calendar is from September 22 to 24 every year. According to the old calendar, the autumnal equinox happens to be the midpoint of ninety days in autumn. Just like the vernal equinox, the sun is almost direct to the equator, and the length of day and night is equal again. It can be said that the autumnal equinox is a very special day. From this day on, the position of direct sunlight continued to move from the equator to the southern hemisphere, and the northern hemisphere began to have shorter days and longer nights. It is recorded in the Spring and Autumn Annals: "The autumnal equinox is half cloudy and half sunny, so it is cold and hot day and night." In astronomy, the autumnal equinox is considered as late summer and early autumn. To be exact, autumn in the northern hemisphere begins at the autumnal equinox. At this time, most parts of our country have entered the cool autumn, and the cold air from the south meets the gradually decaying warm and humid air, resulting in repeated precipitation and temperature drop. As people often say, it's time for "an autumn rain and a cold", but the daily precipitation after the autumnal equinox will not be great. At this time, the field farming in the south and the north is different. In northern China, there is an agricultural proverb that says: "The white dew is early, the cold dew is late, and it is the right time to plant wheat in the autumn equinox." Proverbs clearly stipulate the sowing time of winter wheat in this area; And "White clouds come in autumn equinox, good songs and good rice seeds are everywhere" reflects the planting time of rice in Jiangnan area. In addition, the working people's taboos on the autumnal equinox solar terms are also summarized as proverbs, such as "The autumnal equinox is only afraid of lightning, how much is it?"

Cold Dew

In ancient times, dew was considered as a sign that the weather turned cold. The solar term of the Mid-Autumn White Dew is "dew condensation and white". It is cold in season and autumn, and it is already "dew gas is cold and will condense" into frost. The spring rain surprised the spring and the valley, and the summer was busy and the summer was even hot. Autumn dew, autumn frost, little snow in winter and cold in winter. This is the twenty-four solar terms summed up by the working people in ancient China through continuous practice. At first, they just noticed that the position of the sun was different in different climates at the same time, so they set up a bamboo pole on the ground and observed the change of the shadow length of the bamboo pole. The shortest day of bamboo shadow at noon is the summer solstice, while the longest day of bamboo shadow is the winter solstice. Gradually, they found that one day in spring and autumn was equal to the length of day and night, so they decided to call it the vernal equinox and autumnal equinox, which was too long for production. Other solar terms have also been formulated. Beginning of spring, Rain, Long Summer, Slight Summer, beginning of autumn, Early Summer, Millennium and Early Frost were formulated in the Qin Dynasty. By the Han dynasty, all the 24 solar terms were determined, exactly the same as our current 24 solar terms.

Frost's Descent

The solar term of the first frost means that the weather is getting colder and first frost begins. In the south latitude Sichuan Basin, the average temperature is about 65438 06℃, and there are three solar terms before the first frost day. In the southern valley of the basin, frost can only be seen in the dead of winter. Of course, even at the same latitude, the temperature and humidity of the air close to the stratum are different due to the difference of altitude and topography, and the first frost period and frost day are also different. From a scientific point of view, the saying that "dew becomes frost" is not accurate. The frozen dew formed by dew freezing is hard small ice beads. Frost refers to the phenomenon of crop freezing injury caused by the sudden drop of temperature, and its harmful temperature varies with crops, varieties and growth periods. To form frost, the temperature of the ground or ground objects must drop below 0℃, and the water vapor content in the air on the ground should reach a certain level. Therefore, there may not be frost in first frost, and there may not be frost in first frost.