What do winter solstice and summer solstice mean? The role of the twenty-four solar terms.

Winter solstice is one of the eight festivals in a year. In ancient times, there was a custom of "eight festivals" to worship the gods and ancestors. Winter solstice is regarded as a big holiday in winter. There is a folk saying that winter solstice is as big as a year, so the ancients called it "sub-year" or "off-year". In some coastal areas in southern China, the traditional custom of worshipping ancestors from the winter solstice is still continuing.

The winter solstice marks the minimum height of the sun and the shortest day in the northern hemisphere, but the temperature in winter solstice is not the lowest. On the solstice of winter, the sun shines directly on the ground and reaches the southernmost tip of the year. The sun shines almost directly on the tropic of Capricorn (also known as the winter solstice daily line), and the sun is most biased towards the northern hemisphere.

2. Summer solstice

The summer solstice is the northernmost day of the sun in a year and the limit of the sun's northward movement. The solstice in summer is the turning point of the sun. After this day, I went back, and the direct sunlight point began to move south from the Tropic of Cancer (23 26 north latitude), and the days in the northern hemisphere became shorter day by day.

After the summer solstice, the Tropic of Cancer and its northern region, the midday sun height angle also began to decrease. At the same time, after the arrival of the summer solstice, the stars in the night sky gradually became summer stars.

3, the role of the twenty-four solar terms

"Twenty-four solar terms" reflect the influence of the sun on the earth and belong to the solar calendar category. It is a knowledge system formed by observing the movement of the sun in a year and understanding the changing laws of the four seasons, climate and phenology in a year.

It not only plays a guiding role in agricultural production, but also affects the food, clothing, housing and transportation of ancient people, and even cultural concepts. The current lunar calendar absorbs the solar terms of the trunk calendar as a supplement to the calendar, and is adjusted to conform to the tropic year through the leap method, forming a combined calendar of yin and yang.

Twenty-four solar terms are not only the time criterion promulgated by successive governments, but also the compass to guide agricultural production and to predict cold, warm, snow and rainy days in people's daily life. In the field of international meteorology, the 24 solar terms are known as "the fifth invention of China".