Hailed as China's fifth greatest invention, in addition to papermaking, the compass, gunpowder and printing techniques, the solar terms were created and developed based on ancient Chinese people's observations of celestial bodies and nature.

The ancient Chinese divided the Earth's elliptical orbit around the sun into 24 segments. Each segment was called a specific solar term. These Twenty-four Solar Terms originated in Central China and have been progressively applied nationally.

Conforming to the movement of the Earth and changes in nature, a year is divided into 24 periods, each of 15 days. Following the Start of Spring and Rain Water are Awakening of Insects, Spring Equinox, Pure Brightness, Grain Rain, Start of Summer, Grain Buds, Grain in Ears, Summer Solstice, Minor Heat, Major Heat, Start of Autumn, End of Heat, White Dew, Autumn Equinox, Cold Dew, Frost's Descent, Start of Winter, Minor Snow, Major Snow, Winter Solstice, Minor Cold and Major Cold.

According to phenological observations, the Chinese in ancient times further divided each 15 days evenly into three sections and marked each section with a natural phenomenon. For example, in the first five days from the day of Start of Spring, warm east winds start thawing the frozen land; in the second five days, hibernating insects awaken in their caves; and in the third, river ice starts melting and fish swim among the floating ice fragments.

In the first five days of Rain Water, otters start catching fish. Five days later, wild geese start flying north from their winter sojourn in the warm south. In the last five days of this period, as the name indicates, rain falls and grass grows and trees start budding.

Li Xiutang, a 68-year-old retired senior middle school teacher in Suqian, East China's Jiangsu province, still remembers the proverbs he learned from his grandfather decades ago. Located on the lower stream of the Huaihe River, having four distinct seasons, Suqian is a place where the solar terms can accurately reflect the changes of weather throughout the year.