A set of recently released picture books feature the 24 solar terms which guide Chinese people's work and life. [Photo provided to China Daily]

A set of picture books featuring the scientific principles and customs related to the 24 Chinese solar terms has recently been published.

The ancient Chinese used to divide the sun's annual circular motion into 24 segments, with each measuring around 15 days, to represent a "solar term", which indicates the seasonal climate changes and the consequent life cycle events of plants and animals.

The terms originated in the Yellow River area and the names of the solar terms reflect the observation of the heavens, temperature, rainfall and other natural phenomena in this region.

For more than 2,000 years, Chinese people have used the solar terms as guides for their agricultural practices.

The Twenty-Four Solar Terms, knowledge in China of time and practices developed through observation of the sun's annual motion, was listed as an intangible cultural heritage by UNESCO in November 2016.

The set of picture books, titled The Twenty-Four Solar Terms, comprises four volumes, separately introducing the solar terms-six in each of the four seasons.

The knowledge and stories are told by two cartoon characters-Yangyang (the sun) and Yueyue (the moon)-dressed in traditional Chinese clothes.

According to Chen Xuehui, the chief editor of the book set and deputy general manager of the China Animation Comic Game Group, the books follow the traditional Chinese principle of harmony among heaven, Earth and man.

A set of recently released picture books feature the 24 solar terms which guide Chinese people's work and life. [Photo provided to China Daily]

The position of the Earth when a certain solar term is used, as well as its climate features, are considered the elements of "heaven", while those of "Earth" are represented by animal activities, plant growth and farming.

The roles of "man" are represented by regional customs and folk festival celebrations, related ancient poems, as well as diet.

The principle is also seen in the design of the book covers, with patterns showing the sun's orbit, typical plants of the seasons and representative human activities.

Chen says that the solar terms represent the Chinese people's respect for nature and expectations of a good harvest.

"It is the natural laws that are behind the folk customs," Chen says, adding that the environmentally-friendly theme reflected in Chinese solar terms is consistent with the spirit of the current times.

Meanwhile, Chen wants to change the impression of traditional Chinese culture being monotonous and relatively hard to understand.

Yu Zhenyue, the illustrator of the picture books, says that the internet era provides more opportunities for cartoonists to create works with their painting skills, animation techniques and narration.

According to Chen, it took the team working on the books more than a year to complete the project, and he added that it is also working on a TV anime series on the 24 solar terms.