Chapter 41 The first winter solstice point is moving

Before the Han Dynasty, people did not know that the winter solstice point was moving, and everyone was working hard to determine the evening stars of each solar term, thinking that once the evening stars of each solar term were determined, they would remain unchanged forever.At the same time, calendarists are also exploring the position of the sun at the beginning of the year and the winter solstice in the calendar.Due to the strong sunlight, the sun covers all the stars and planets at sunrise, so it is impossible to directly measure the position of the sun in the starry sky during the winter solstice. However, astronomers in the Warring States Period still used an indirect method to derive the position of the sun during the winter solstice. Morning glory.

Since pre-Qin astronomers have always used the dynamics of stars' rising, setting, and mid-heaven to determine the seasons, this method is indeed an effective way to determine the seasons, but it also creates an illusion for people, thinking that stars in the evening The relationship to the seasons never changes.It is precisely because of this understanding that many astronomers did not consider re-measurement of the sun's position at the winter solstice when the calendar was changed at the beginning of the Western Han Dynasty, and still used the value measured by the predecessors.At the end of the Western Han Dynasty, when Liu Xin compiled the calendar of the three systems, he observed the winter solstice point, and the result he obtained was that the winter solstice point was "four degrees and five minutes before the advance and retreat of the ox", that is, the position of Jianxing.Jianxing is the constellation located between Dousu and Niusu; the distance between Dousu and Niusu is 26 degrees, and four degrees in front of Niu is 21 degrees in Dousu. This value is actually relatively correct, but Liu Xin still dare not affim.It was not until the Eastern Han Dynasty and the reform of the calendar that Jia Kui clearly pointed out that the sun in the winter solstice was at 21 degrees in Dousu, and this result coincided with Liu Xin.Jia Kui affirmed his measured results, but he did not consider why his measured results were inconsistent with those of his predecessors.It can be seen that before the Eastern Han Dynasty, Chinese astronomers confirmed the movement of the winter solstice point through their own independent observations.