However, as time passes and people have relied more on science and technology, the solar terms seem less useful than they were in ancient times. Living a fast-paced life in modern cities of steel, cement and glass, people, working around the clock, have lost their sense of time and connection with nature. Depression and insomnia are blighting an increasing number of people's lives.

"Now many people live their life, not according to the instruction of the Twenty-four Solar Terms, but deadlines," says Li Min, astronomer and a former professor of Nanjing University.

"The decrease of sunlight is related to depression in winter," he says.

Living organisms are also influenced by gravity relationships between the sun, the Earth and the moon, he says, including when to rest and when to work.

"As we see, when people refer to deadlines to adjust their daily schedules, rather than the natural rules developed during the evolution of human beings over tens of thousands of years, many fall ill and some even die suddenly due to overwork," he says.

Scientists have been trying to decipher the riddle of the circadian rhythm of living organisms. In 2017, the Nobel Prize in medicine was awarded to three scientists for their discoveries of molecular mechanisms controlling the circadian rhythm, which explain how plants, animals and humans adapt their biological rhythm to synchronize it with the Earth's revolutions.

"Although the solar terms are a heritage left by ancient agricultural society, it is still meaningful to modern society," Yu was quoted as saying in a previous interview.