Shichen — astrology wiki

Twelve intervals, one declared clock

HKO describes shichen as branch-labelled hours and gives their correspondence to modern clock intervals. Its historical account distinguishes this branch-only naming from the later addition of hour stems derived from the day stem.

The reference sequence is Zi 23:00–01:00, Chou 01:00–03:00, Yin 03:00–05:00, Mao 05:00–07:00, Chen 07:00–09:00, Si 09:00–11:00, Wu 11:00–13:00, Wei 13:00–15:00, Shen 15:00–17:00, You 17:00–19:00, Xu 19:00–21:00 and Hai 21:00–23:00.

Hong Kong Observatory · stem–branch sequence and hour tables ↗

Apply the interval to the selected clock

In Atlas, enter the recorded civil time with its timezone first. Choose civil, local mean solar or local apparent solar time in the explorer. The resulting clock reading is what selects the hour branch. Applying the same interval table to different clock readings can produce different branches near an edge.

The implemented intervals include their start and exclude their end. For example, a displayed 00:59 remains Zi; at 01:00 it becomes Chou. This example describes the selected clock, not an instruction to change the recorded birth time.

An hour branch is not the whole hour pillar

The day-boundary setting determines the cycle day used by the hour-stem calculation. Zi spans midnight, so the same Zi branch can accompany different hour stems when the selected cycle day changes.

Try the original Atlas example on the Four Pillars guide: 7 January 2000 at 23:30, timezone UTC, civil clock. The midnight option gives day Jia-Zi and hour Jia-Zi. The 23:00 option gives day Yi-Chou and hour Bing-Zi. The unchanged Zi branch does not mean the full readings are identical.

This exercise follows Atlas’s two implemented conventions. It does not cover the separate late-Zi approach that retains one day pillar while deriving the hour stem from the following day.

A practical check before interpretation

Read the complete hour pair alongside the selected clock, displayed date and cycle date. If another service disagrees, compare these inputs and conventions before interpreting the difference. A rounded time near an interval edge may not support one definite hour pair.

When the birth time is unknown, a precise hour pillar is unavailable. Choosing a solar clock cannot recover the missing time. Preserve the recorded uncertainty and use only the parts of the chart supported by the available data.