The Vernal Equinox is one of the twenty-four solar terms and the fourth solar term of spring. It occurs when the sun's ecliptic longitude reaches 0°, and it takes place between March 19th and 22nd of the Gregorian calendar each year. The Vernal Equinox holds significant importance in astronomy. On this day, the sun is directly above the equator, and the day and night are of equal length in both the northern and southern hemispheres. From this day onward, the sun's direct path moves northward from the equator towards the northern hemisphere, and in the northern hemisphere, the days begin to be longer than the nights. In the southern hemisphere, the opposite is true. In terms of climate, there are also distinct characteristics. After the Vernal Equinox, except for the Qinghai-Tibet Plateau, the northeastern region, the northwest region, and the northern part of the north-central region of China, the entire country enters a bright spring. 
The word "fen" in "Spring Equinox" has two meanings. The first meaning is "seasonal division", traditionally, the period from the beginning of spring to the beginning of summer is regarded as spring. The Spring Equinox day falls exactly in the middle of these two seasons, thus dividing spring evenly. The second meaning is "equal day and night". On the Spring Equinox day, the sun shines directly on the equator, making the day and night of equal length, each lasting 12 hours. The climatic characteristics of the Spring Equinox are warm weather and bright sunshine. During this season, in Chinese folk customs, there are activities such as flying kites, eating spring vegetables, and standing eggs. 
Meaning of the section title 
The term "Spring Equinox" means "half" - it signifies division into two. It represents the equal division of day and night, and the balance of cold and heat. Additionally, the Spring Equinox also signifies the division of the spring season. Traditionally, the period from the beginning of spring to the beginning of summer is considered as spring. The Spring Equinox falls exactly in the middle of these three months. Therefore, in ancient times, it was also called "Midday", "Equal Day and Night", or "The Second Month of Spring". On the Spring Equinox, the sun shines directly on the Earth's equator, resulting in equal day and night. According to the work "The Explanation of the Seventy-Two Solar Terms" by Yuan Guicheng: "In the middle of February, 'division' means half. This is when the ninety days are halfway through, so it is called 'division'." In "The History of the Ming Dynasty - Astronomy": "The division point is where the intersection of the ecliptic and the tropic occurs. When the sun reaches this point, day and night are evenly divided." Also, in "The Spring and Autumn Exposition": "The Spring Equinox is when yin and yang are evenly divided. Therefore, day and night are equal and cold and heat are balanced." In the lunar calendar: "When the Heavenly Stems point to the Rabbit, it is the Spring Equinox. It covers a full circle, and the day and night on both the northern and southern hemispheres are evenly divided (except at the poles). It is also the halfway point of spring, so it is called the Spring Equinox." 
Agricultural activities 
As an old saying goes: "When the vernal equinox arrives, the wheat sprouts; fertilization and water supply must follow closely." Every spring rain brings warmer weather, and after the spring rain, it's time to plow the fields. The busy season of spring is about to begin, and spring management, spring farming, and spring planting will enter a busy phase. After the vernal equinox, overwintering crops enter the growth stage, and field management needs to be strengthened. Due to the rapid rise in temperature, the water demand is relatively large, and farmers need to strengthen water storage and soil conservation. 
In the northern regions with scarce rainfall in spring, efforts should be made to carry out spring irrigation, ensure adequate water supply for the emergence period, apply fertilizers during the tillering stage, and take precautions against late frost damage. In the south, the work of draining water and preventing waterlogging should continue. The early rice seedling cultivation in the Jiangnan region and the early rice film seedling cultivation in the Jianghuai region have already begun. In early spring, with frequent changes in temperature, it is necessary to soak and germinate the seeds when the cold air arrives, and sow promptly when the cold air ends. 
In the northern regions with scarce rainfall in spring, combating spring drought remains an important agricultural activity during the vernal equinox. In these areas, it is necessary to promptly carry out spring irrigation, ensure proper watering for the emergence period, apply appropriate growth-promoting fertilizers, and make adequate preparations for resisting spring drought and frost damage. 
In spring, when the weather gradually warms up, cold air often invades. Especially in the Jiangnan region and along the Yangtze River, when the cold air from the north meets the warm and humid air from the south, continuous rainy weather occurs in spring, causing the temperature to drop significantly. This is what people commonly refer to as "reverse spring cold".