“The ruler is supposed to take his cue from heaven in arranging for the conduct of government. When Heaven displays phenomena of an unusual character it is considered right that the ruler should regard such as a warning, and take steps to bring his administration more into line with the revealed will of Heaven.
It would seem to follow logically from that, if the ruler acts in accordance with what is right, Heaven should display a correspondingly favorable aspect. But is that really so?”- Wang Anshi
Wang Anshi, throughout his career, had been continuously open to attacks based on astronomical phenomena. That is to say, the location of Venus in the sky, or the occurrence of an eclipse, was used as signs of Heaven’s disfavor of Wang’s regime. It followed, naturally, that he took a strong interest in astronomy. If the state could predict the motion of heaven, after all, it followed that it could determine its will.
This is where Shen Gua entered the scene. He had been a loyal supporter of the reforms of Wang Anshi, and had served heroically in the war against the Liao, leading armies to victory against the northern barbarians. With the prestige he received, he was able to turn his attention to his first love, astronomy.
Shen Gua, during his term as the head of the Directorate of Astronomy, carried out a program that would revolutionize Chinese astronomy.
Traditional Chinese astronomy had focused on providing mathematical formulas, for predicting the general movements of the heavens. Shen Gua, however, proposed something much more advanced: a full fledged physical model for the movement of the heavens.
Shen Gua had long been puzzled by the movement of the planets; in particular, by the way that certain planets appeared to move backwards in the heaven at certain points of the year[1]. His initial explanation relied upon what he called “willow leaves”. As the planets orbited the Earth, they periodically moved, in their orbits, in the shape of a willow leaf.
It is, for its time, an elegant model. But Shen Gua was aware that he would need proof to verify his theory, and during his time as the Director of Astronomy, he “observed the positions of the moon and planets at dusk, midnight, and dawn, to the nearest fraction of a degree, and to establish a register in which they are to be recorded.”[2]
This is done, but the results, when they are completed, and analyzed using proto-trigonometry, does approximate with his theory. Shen Gua is, for the moment, satisfied, although he can identify several flaws with his theory. The willow leaves, for instance, are actually circular.
By 1090, the imperial astronomers, who are still scanning the heavens, have tenatively prepared to accept the theory of willow leaves.
[1] The planets beyond Earth’s orbit move in the same direction around the sun as Earth. But because Earth’s orbit is smaller, the Earth overtakes the outer planets. When this happens, the planet first appears to stop drifting eastwards in the heavens, and heads west. As the earth passes the planet, the planet begins to travel east again.
In OTL, the justification in the western world was epicycles. The Chinese didn’t really consider it until Shen Gua.
[2] Hey, these are his words. And the fact that he was aware that the measurements should be done to the nearest fraction of a degree is a testament to the accuracy that would have been available to him. Even in OTL, he devised a series of astronomical tools to increase accuracy.
