Ancient Study of the Winter Solstice and the Astronomical Inferences in YaoDian

The study of the formation of ancient concept of the winter solstice helps to further explore the issue of seasons discussed in the pre-Qin documents.As YaoDian did not clarify astronomically the specific beginning and ending of a year,later scholars made various inferences.They identified four phases of time-midspring,midsummer,midautumn and midwinter,but could not measure the specific time of the vernal equinox,the autumnal equinox,the summer solstice and the winter solstice due to inadequate time measurement and recording,let alone the cyclic features of the winter solstice.All of these uncertainties made it impossible to determine the division of years.