The Chinese Zodiac is based on Jupiter's 12-year orbit around the Sun.

The Chinese Zodiac is rooted in the "Sui-xing" (Year Star) system, the ancient Chinese name for Jupiter. During the Zhou Dynasty (1046–256 BCE), astronomers tracked Jupiter's movement and discovered it takes approximately 11.86 Earth years to complete one full revolution around the Sun. To simplify their calendar system, they rounded this period to 12 years and created the 12 Earthly Branches.Each branch corresponds to one of the 12 years in Jupiter's orbital cycle and is represented by a specific animal. This celestial timekeeping system predates the modern Gregorian calendar by centuries. The 12-year cycle is further integrated with the five elements—wood, fire, earth, metal, and water—to create a complete 60-year sexagenary cycle that adds additional complexity and meaning to the system.Jupiter's prominence in the sky made it an ideal cosmic clock for ancient observers. As the largest planet in our solar system, its visibility and predictable path were crucial to the system's success. The Han Dynasty (206 BCE–220 CE) formalized these observations into the astrological framework used today. Modern calculations confirm that Jupiter's sidereal period is 4,332.59 days, which aligns remarkably well with the ancient 12-year model. This demonstrates how early civilizations applied real planetary physics to develop cultural and social systems that have endured for millennia.