Which solar term was first determined in ancient China?

The vernal equinox ranks fourth among the 24 solar terms and is one of the earliest solar terms in ancient China. As early as the Spring and Autumn Period and the Warring States Period, China began to measure the length of the midday sun shadow with earth gauge. Through this ancient method, the ancients in China determined four solar terms: winter solstice, summer solstice, vernal equinox and autumn equinox. During the Qin and Han Dynasties, China had a complete concept of twenty-four solar terms.

Every year on March 2 1 day, the sun reaches the hottest meridian zero, which is vernal equinox. The vernal equinox means the average distribution of time between day and night, every 12 hours. The vernal equinox is in the first three months of the year. In the spring equinox season, the average temperature in China is stable at around 10 degrees Celsius, and in the spring of meteorological significance, agricultural production has also entered the peak season.

In the pre-Qin period, China had four seasons. "History? Yao Dian recorded four solar terms: the sun is always short, and the day is midnight, representing the vernal equinox, autumnal equinox, summer solstice and winter solstice respectively. In ancient China, the vernal equinox was divided into three stages: waiting for the arrival of mysterious birds; Second, wait for Reynet to make a sound; Third, wait for the electric bird? This refers to the swallow, right? Equinox? . ? Autumn equinox? It is a migratory bird. The vernal equinox is one of the earliest solar terms in China, which is both a solar term and a festival. Since the Zhou Dynasty, there have been ceremonies to worship the sun at the vernal equinox. Later, successive dynasties gradually formed a ritual system about the vernal equinox and the autumn equinox.

On the vernal equinox, there are many folk customs, such as hiking, flying kites, sending spring cattle and eating spring vegetables, and there is also a very interesting custom of laying eggs. Why do eggs stand upright at the vernal equinox and autumnal equinox? Scientists analyzed the reasons and found that at the vernal equinox and autumnal equinox, the length of day and night in the northern and southern hemispheres is the same, and the earth axis and the orbital plane around the sun are in a relatively balanced state, which is conducive to egg-shaped erection. From the perspective of an egg, you can choose a new egg that has been laid for four or five days. This time, the yolk of the egg sinks and the center of gravity of the egg drops, which makes the success rate of the egg standing up higher.