One of the seven celestial bodies, Mercury, Venus, the moon, the sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by ancient astronomers to revolve in the heavens about a fixed Earth and among fixed stars.

• 古行星能够用肉眼看到七个天体之一，水星、金星、月球、太阳、火星、木星和土星，古代天文学家认为它在天空中围绕着固定的地球和固定的恒星中旋转