Chinese astronomy divides the year into twenty-four parts based on the longitude of the sun on the ecliptic, which are called the "Solar Terms". This shows the relationship between the universe, season, climate and agriculture. To date, it has functioned as a complete weather calendar , to guide the agricultural production in China.

What is a Solar Term ?

A solar term is any of the 24 points in traditional East Asian lunisolar calendars that matches a particular astronomical event or signifies some natural phenomenon. The points are spaced 15° apart along the ecliptic and are used by lunisolar calendars to stay synchronized with the seasons. Solar terms originated in China, then spread to Korea, Vietnam, and Japan. Each solar term or node is the moment when the sun reaches one of twenty-four equally

spaced points along the ecliptic, including the solstices and equinoxes, positioned at fifteen degree intervals.

Because the calculation is solar based, these nodes fall around the same date every year in solar calendars, but do not form any particular pattern in the Chinese calendar. Calendars with the 24 seasonal markers are published each year in farmers' Chinese almanacs.

What are the Twenty-four Solar Terms and their meanings ?

Each Jieqi (solar term) was given a name that signified the related meteorological and phenological changes on the earth.

The table below show the Twenty-four Solar Terms :

Why was the Twenty-four Solar Terms was invented by ancient Chinese?
In ancient times, agriculture was the economic mainstay of China and its people, and the purpose of establishing a calendar was to regulate agricultural production. Chinese ancients discovered through astronomical observation, that during the earth's 12-month orbit around

the sun, its changing position gave rise to periodical changes in climate and thus distinctive farming seasons. They subsequently designated 24 positions within the earth's orbit, calling them the 24 Jieqi (24 solar terms).

Chinese months follow the phases of the moon, and as a result, they do not precisely follow the seasons of the solar year. To help farmers to decide when to plant or harvest crops, the Chinese calendar is marked with 24 seasonal markers, which follow the solar year.

How does the Twenty-four Solar Terms come into existence and develop?

The Twenty-four Solar Terms come to being and develop in close relationship with Chinese agricultural production, and?today the year comprises of 24 Solar Terms. During the Shang Dynasty they only used four solar terms; the Zhou Dynasty (11th century BC - 221BC), used eight; but it was in the Western Han Dynasty (206BC - 24) that the 24 terms were finally decided upon.

At the initial stage of agricultural development, people began to explore the seasonal rule in the agricultural production to meet the needs in seeding, harvesting and other activities. Gradually, they formed the concept of "Seed in Spring, grow in Summer, Harvest in Autumn and Store in Winter". During the Spring and Autumn Period, the agricultural production was high, subject to the seasonal changes with the invention of iron tools, thus forming the concept of Solar Term. At that time, the method of tugui was used to measure the shadow of the sun for determining the solar terms. Initially, there were only the Summer Solstice and the Winter Solstice. Later added were the Spring Equinox, the Autumnal Equinox, the Beginning of Spring, the Beginning of Summer, the Beginning of Autumn and the Beginning of Winter.

?Astronomically, the Twenty-four Solar Terms are defined according to the position of the sun on the ecliptic. 0 degree of celestial longitude is the Spring Equinox and the every solar term matches the passage 15 degrees. As a result, there come Twenty-four Solar Terms as it passes by 360 degrees. Later, the Twenty-four Solar Terms were introduced into North Korea, Japan and other neighboring countries.