What is the solar term of equal length between day and night in the old nest?

The nest as long as day and night is also the habitat of mysterious birds. The solar term is: vernal equinox.

At the vernal equinox, the direct point of the sun is on the equator, and then the direct point of the sun continues to move northward, so the vernal equinox is also called "rising equinox"; In ancient times, it was also called "Japan-China", "Day and Night" and "Mid-spring Moon". The vernal equinox is an important solar term, which is of great significance in astronomy: the northern and southern hemispheres are equally divided day and night; Since then, the direct position of the sun has continued to move from the equator to the northern hemisphere. The days in the northern hemisphere are getting longer and shorter, and the nights in the southern hemisphere are getting shorter and shorter.

During the spring equinox, China has entered a beautiful spring scenery except the Qinghai-Tibet Plateau, Northeast China, Northwest China and North China. At this time, the climate is mild, the rain is abundant and the sun is shining, and the wintering crops in most parts of China enter the spring growth stage; "Li Mingshi Yi": "The dividing line, the point where Huangchi meets, the sun is here, and the day and night are equally divided." Therefore, the significance of the vernal equinox, first, refers to the equal division of day and night, each of which is 12 hours; Second, the vernal equinox is just in the middle of three months in spring, and spring is equally divided.