Period 9 flying star n classical fengshui, the “Three Cycles and Nine Periods” [三元九运 ] spans over 180 years. The Three Cycles refer to the Upper, Middle and Lower Cycle, where each cycle consists of three fengshui periods. There are nine periods in total, which corresponds with the 9-grid Flying Stars Chart. Each fengshui period lasts 20 years, and is under the influence of a Star. https://www.wayfengshui.com/