Emperor Yao (a legendary scholar ruler who reigned from 2357 to 2255 B.C.) ordered astronomers to study the times when the sun rose, and the length of its shadows. This led to the calculation that there are 365 1 / 4 days in a year, which is further divided into four seasons.
從展示的資料和圖表中可知，堯帝時，就命天文官測日出的早晚，日影的長短，得知一年有三百六十五又四分之一天，又置閏月。