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People: Habibullah Kalakani

Shen Kuo, to allow more accurate astronomical …

Years: 1077 - 1077

Shen Kuo, to allow more accurate astronomical observations and recordings, has improved the technical designs of the rotating armillary sphere, the gnomon, the clepsydra clock, and the sighting tube.

He has calibrated the standard diameter of the sighting tube's width, hence allowing the observation of the polestar indefinitely (which had shifted since the time of Zu Geng in the fiftht century).

With these, Shen and Wei have attempted to predict the mean speeds of the planets as well as the accurate positions of the planets in their orbits.

They have established a system of observing and recording on a star map the exact coordinates of the planets, done three times a night for a total of five years.

Shen Kuo has made a cosmological hypotheses in explaining the variations of planetary motions, including the concept of retrogradation.

On the other hand, Wei Pu realizes that the old calculation technique for the mean sun is inaccurate compared to the apparent sun, since the latter is ahead of it in the accelerated phase of motion, and behind it in the retarded phase.

Hence, he incorporates solar motion into the eclipse theory.

The Song Dynasty astronomers of Wei's day still retain the lunar theory and coordinates of the earlier Yi Xing (683-727), which after three hundred and fifty years has devolved into a state of considerable error.

To fix this, Shen and Wei have kept similar astronomical records, three times a night over five years, for the orbital path of the moon.

Wei and Shen's work is deeply opposed by the officials and fellow astronomers at court, who are offended by their insistence that the coordinates of the renowned Yi Xing are inaccurate.

The elite, well-educated ministers and leading astronomers are also insulted by the fact that Wei Pu had been born a commoner, yet holds more expertise in his field than many of them.

When Wei and Shen make a public demonstration using the gnomon to prove the doubtful wrong, the other ministers reluctantly agree to correct the lunar error.

Although correcting the lunar error is a success, the other ministers and officials eventually dismiss Wei and Shen's recorded course plotting of planetary motions, while the court relies upon the inefficient and older model.

This means that only the very worst errors are corrected for planetary motion.

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