measurement of the distance between the pole star and true north that could be used for navigation. Shen achieved this by making nightly astronomical observations along with his colleague Wei Pu, using Shen's improved design of a wider sighting tube that could be fixed to observe the pole star indefinitely. Along with the pole star, Shen Kuo and Wei Pu also established a project of nightly astronomical observation over a period of five successive years, an intensive work that even would rival the later work of Tycho Brahe in Europe. Shen Kuo and Wei Pu charted the exact coordinates of the planets on a star map for this project and created theories of planetary motion, including retrograde motion. Foreign influences Indian astronomy Buddhism first reached China during the Eastern Han dynasty, and translation of Indian works on astronomy came to China by the Three Kingdoms era (220–265 CE). However, the most detailed incorporation of Indian astronomy occurred only during the Tang dynasty (618–907), when a number of Chinese scholars—such as Yi Xing—were versed in both astronomy. A system of Indian astronomy was recorded in China as Jiuzhi-li (718 CE), the author of which was an Indian by the name of Qutan Xida. The astronomical table of sines by the Indian astronomer and mathematician Aryabhata was translated into the Chinese astronomical and mathematical book Treatise on Astrology of the Kaiyuan Era (Kaiyuan Zhanjing), compiled in 718 CE during the Tang dynasty. The Kaiyuan Zhanjing was compiled by Gautama Siddha, an astronomer and astrologer born in Chang'an, and whose family was originally from India. He was also notable for his translation of the Navagraha calendar into Chinese. The Chinese translations of the following works are mentioned in the Sui Shu, or Official History of the Sui dynasty (seventh century): Po-lo-men Thien Wen Ching (Brahminical Astronomical Classic) in 21 books. Po-lo-men Chieh-Chhieh Hsien-jen Thien Wen Shuo (Astronomical Theories of Brahman.a Chieh-Chhieh Hsienjen) in 30 books. Po-lo-men Thien Ching (Brahminical Heavenly Theory) in one book. Mo-teng-Chia Ching Huang-thu (Map of Heaven and Earth in the Matangi Sutra) in one book. Po-lo-men Suan Ching (Brahminical Arithmetical Classic) in three books. Po-lo-men Suan Fa (Brahminical Arithmetical Rules) in one book. Po-lo-men Ying Yang Suan Ching (Brahminical Method of Calculating Time) Although these translations are lost, they were also mentioned in other sources. Islamic astronomy in East Asia Islamic influence on Chinese astronomy was first recorded during