Editing Earthly Branches (section)

== History ==
The earliest attested use of the Earthly Branches and Heavenly Stems is in recording cycles of days.{{sfnp|Smith|2015}} The ten Heavenly Stems provided names for the days of the week during the [[Shang dynasty]] ({{circa|1600|1050&nbsp;BC}}). The Branches are at least as old as the Stems, with archaeological evidence suggesting they may actually be older.

There are several theories about the origin of the Earthly Branches prior to the advent of the historical record. One theory is that the Earthly Branches were adapted from observations of the planet [[Jupiter]] ({{zhi|l=Year Star|c=歲星|p=Suìxīng}}), whose [[orbital period]] is roughly twelve Earth years long. Jonathan Smith has proposed that the first meanings of the earthly branches, predating the Shang, were [[phases of the moon]], with the Heavenly Stems at that point referring to divisions of the ecliptic. After being adopted as a calendar these would have lost their clear lunar reference, permitting their re-purposing for Jupiter stations.{{sfnp|Smith|2011|pp=222}}

In the context of [[Chinese cosmology]] becoming increasingly sophisticated during the [[Warring States period]] ({{circa|475}}{{snd}}221&nbsp;BC), the 12-, 10-, and 60-cycles began to be applied to units of time other than days.{{sfnp|Smith|2015}}