Comets (彗星 Huìxīng) have been observed and recorded in China since the Shang Dynasty (1600-1046 BC). The set of comet illustrations shown above is from a silk book (帛书 Bóshū) written during the western Han period. The different shapes and characteristics of the comet tails were outlined and on some of the comets, differences in the appearance of the core of the comet were noted. From the Yin period of the Shang Dynasty to the end of the Qing Dynasty in 1911, comets were observed and recorded more than 360 times. In 635 BC, Chinese astronomers pointed out that the comet tail always pointed away from the sun. From the Spring and Autumn Period to 1910 at the end of the Qing Dynasty, 31 observations of Halley's Comet were recorded according to the Beijing Ancient Observatory. Other sources put the number at 30. The first verified record of Halley's Comet was made in China in 240 BC. However, in 613 BC in the Spring and Autumn Annals (春秋 Chūnqiū) of Confucius, reference was made to a comet. It said: "In July, there was a comet that entered the Big Dipper." (“秋七月，有星孛入于北斗。” qiū qīyuè, yǒu xīngbèi rù yú běi dǒu). This may have been a reference to the appearance of Halley's comet that would have been in 620 BC. Europeans did not record its appearance until much later, but it was Edmond Halley who hypothesized that the comet that astronomers in Europe had recorded over time was actually the same comet returning again and again and predicted that it would return and when. He urged Newton to develop the mathematics that would let him calculate the orbit. With Newton's new calculus Halley was able to show the orbit of the comet and establish the 76 year cycle of its appearance. The timing of the comet actually varies based on what objects it encounters along the way. When passing Jupiter, the comet slows and is late arriving at Earth. Comets are relatively small bodies so they are strongly affected by the gravitational fields of their larger cousins.