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Book copied on silk, Divination Based on the Observation of Five Planets Western Han Dynasty Length 221cm, width 49cm  Unearthed from Li Xi’s Tomb This is the world’s oldest existing work of astronomy, and is made up of two parts, the divination text and the positional tables. The positional tables record the positions of Venus, Jupiter and Saturn for 70 years, from the first year of the reign of Qin Shihuang (BC246), to the third year of the reign of Emperor Wen of Han (BC177). Venus’ synodic period was measured at 584.4 days, just 0.48 days more than today’s measurement of 583.92 days. Saturn’s synodic period was measured at 377 days, just 1.09 days less than today’s measurement, and its sidereal period was measured at 30 years, 0.54 years more than today’s measurement of 29.46 years. This information reflects the advanced astronomical achievements made at the time in China.