This is the Spring Equinox, one of the twenty-four solar terms.

Name: This is the Spring Equinox, one of the twenty-four solar terms.
Author: Gao Chunxiang, Shao Min Text; Xu Mingzhen, Li Jing Images

The 24 Solar Terms are a unique intangible cultural heritage of China. Children know that spring has arrived, but they don't understand what "Spring Equinox" means, or how ancient people calculated it.