The months were so named after the moon; the new moon marking the end of an old month and start of a new month; the full moon occurring in the middle of the month, after which the month was named.
Šen Kuo (1031–1095) je v času dinastije Song izdelal prispodobo, kjer je enačil naraščanje in pojemanje Lune s srebrno odbijajočo kroglo, ki bo izgledala kot polmesec, če jo potresemo z belim praškom in pogledamo od strani.