Meanwhile, tenmondo was not considered as important as onmyodo ('the way of Yin and Yang', an occult divination system based on the Taoist theory of the five elements) in the ritsuryo nation of Japan, and, as a rule, observations of the sky were conducted only at fixed times, such as from 8 PM to 10 PM and from 4 AM to 6 AM.
もっとも、天文道そのものが陰陽道と比較して日本の律令国家においては、余り重要視されたとは言えなかった部分があり、夜空の観測も平常は戌の刻と寅の刻の定時観測のみであったとされている。