Zi Wei Dou Shu (Chinese: 紫微斗數), commonly referred to in English as Purple Star Astrology, is a form of fortune-telling in Chinese culture. The study of destiny (Chinese: 命學, ming xue) is one of the five arts of Chinese metaphysics. Along with the Bazi chart, Zi Wei Dou Shu is one of the most renowned fortune-telling methods used in this study. Much like western astrology, Zi Wei Dou Shu claims to use the position of the cosmos at the time of one's birth to make determinations about personality, career and marriage prospects, and more. Traditionally, Zi Wei Dou Shu is considered to have been created by a Taoist named Lu Chun Yang (呂純陽) during the Tang Dynasty. It was further developed by Chen Xi Yi (陳希夷) during the Song Dynasty and later on by Luo Hong Xian (羅洪先) during the Ming Dynasty to its present-day form. Its exact origin, however, is still debated among different schools. Unlike the more commonly known Four Pillars of Destiny system of birth-chart divination, Zi Wei Dou Shu is based on a purely lunar calendar and the position of the night sky. By contrast, Bazi is tied to the sexagenary cycle system of timekeeping, which is often mapped to traditional Chinese solar terms. Some believe that this difference makes the two systems complementary rather than competitors. The study of destiny (命學, ming xue), of which Zi Wei Dou Shu is a part, has traditionally been closely intertwined with astronomy. Historically, gifted astronomers and astrologers were recruited as officials to work in Imperial Courts during the dynastic eras, producing astrological charts for the emperor, as his personal fate had a direct bearing on his kingdom. The court astrologers also played an important role in determining the successor to the throne. Astrologers observed the stars and noticed that among so many stars, only one was seemingly stationary while the rest revolved around it. This star was named the "Emperor Star" (紫微星)--the celestial equivalent of the Emperor and known in the West as Polaris.