Five days in a phase, three phases in a term Following this kind of observation, more than 1000 years elapsed step by step, up to the Spring and Autumn Period, when the ancients established the two days of the year in which "day and night are equally long," which are known in astronomy as the vernal and autumnal equinoxes.
順著這樣的觀察，足足過了一千多年，到春秋時代，古人又確立了一年中「日夜等長」的兩個日期，也就是天文學上的「春分」和「秋分」。