To China, founded as it was on agriculture, the importance of sunlight could hardly be greater. Because of this, integrating information concerning the movements of the sun into the lunar calendar for the consideration of the farming folk was an impressive feat of learning.
日照對於以「農」立國的中國來說，影響非同小可，因此要怎樣在陰曆裡面，加入一點太陽運行的資訊以供農民參考，就是一門大學問了。