The astronomical understanding of the heavens in "Hwangje-Naegyeong" can be divided into three main fields: the theory of cosmos, astronomy and calender. "Hwangie-Naegyeong" comprised the theory of cosmos, astronomy and calender established in the Han period. Astronomy was to describe the heavenly world and to interpret its phenomena. Calendar was to make numerical representations of the observations of all kinds of celestial bodies and to give them number-mystical meanings. Theory of cosmos treated what ancient Chinese speculated on the structure of the heavens including the earth. These three fields developed independently. However, they can also be be combined into one tradition, the astronomical knowledge. In the Han period that the astronomical knowledge grew from the mere accumulation of primitive knowledge to the established form. Throughout the Chinese history, the essential contents of astronomical knowledge including the theory of calendar, did not change much from what they were in Han period. "Hwangje-Naegyeong" use the lunisolar calendar(太陰太陽曆) and the Calendar in the late Han period(後漢四分曆). The use of the subdivisions of the seasons(24節氣) and the leap month(閏月) in "Hwangje-Naegyeong" means that it adopted the lunisolar calendar. Also "Hwangje-Naegyeong" adopted the Calendar in the late Han period by the four points: "Hwangje-Naegveong" ruled the circulation of the universe(周天度數) at 365, 1/4 terms, use the The Twenty Eight Constellations in astronomical observation, view the heavenly body by the ecliptic(黃道) and mark down year by the Heavenly Streams & Earthly Branches(干支紀年), The 24 solar terms is made by amount of Yang-Gi(陽氣) and samyum and samyang(三陰三陽) represent the amount of Yang-Gi in the earth.