Researching a historical Chinese date
A historical date has two parts: the wording preserved in a document and its proposed equivalent in another calendar. Keeping them together allows the conversion to be checked or revised without losing the original information. The main decisions concern the era, the identity of the lunar month and the civil-calendar convention used for the result.
The original date
Transcribe the complete date before converting it. A reign-year number needs its era name and political context. A lunar month needs any leap designation. A day may be given by number, by its Ganzhi name from the stem-and-branch cycle, or by both.
| Field | What to preserve | Why it matters |
|---|---|---|
| Political context | Dynasty, state or ruler | Similar era names can belong to different governments |
| Era | The complete reign or republican-era name | A numbered year alone is ambiguous |
| Year | Number and any cyclical designation | Provides the chronological framework |
| Lunar month | Number or named month, including a leap marker | An ordinary month and a leap month bearing the same number are different intervals |
| Day | Day number and any stem-and-branch name | The two forms can check one another |
| Calendar wording | “Old calendar,” “new calendar,” paired dates or equivalent wording | Helps identify the intended month-and-day system |
| Document context | Shelfmark, page, inscription position and corrections | Allows the reading to be checked against the document |
A damaged character or missing day should remain unresolved until other information identifies it. A month-only date gives an interval, not its first day. Similarly, a lunar year cannot simply be replaced with a Gregorian year number: its beginning and end usually fall inside Gregorian years rather than on January 1.
Republican-era records require a separate distinction. Minguo numbering begins with 1912 as year 1, but an informal record can pair that year label with either Gregorian or lunar months. The year number alone does not identify the month system.
Historical tables and civil-calendar conventions
The reference must match the purpose of the conversion. To identify the date used by a historical writer, a contemporary annual calendar or a reconstruction of that period's calendar is more relevant than an unrestricted projection of modern rules into the past.
| Reference type | What it supplies | Main point to establish |
|---|---|---|
| Contemporary annual calendar | The dates printed for a particular year | Its year, jurisdiction and edition |
| Historical conversion table or reconstruction | A proposed sequence of historical months and days | The period covered and the calendar assumptions |
| Modern astronomical calculation | New moons and solar terms under a stated model | The reference time and rules used to turn events into dates |
| Paired dates in a document | A correspondence recorded by its writer | The identity of both calendars and the reliability of the reading |
The civil date on the other side of the conversion also needs a label. Julian and Gregorian dates use similar-looking month names and numbers but can identify different days. A proleptic Gregorian date extends Gregorian rules backward to a time before their historical introduction.
Chinese Calendar Atlas supports civil dates from AD 1 through AD 2100. It uses Julian civil dates through 1582-10-04, followed by Gregorian 1582-10-15. Those dates are consecutive days in that convention. The transition skips ten date labels while the sequence of days continues uninterrupted. This software convention does not mean that China adopted the Gregorian calendar in 1582, or that the Atlas reproduces every historical Chinese calendar used across its supported range.
Month starts, cyclical days and date boundaries
Establish the year and month before checking the individual day. Confirm whether the month is ordinary or leap, then locate its first day in the chosen calendar. Lunar day d is d − 1 elapsed days after the month's first day. Count elapsed days across any Julian/Gregorian transition rather than adding to the printed day number alone.
The month's length provides another check. A date numbered 30 requires a thirty-day month. A Ganzhi day name can then be compared with the name expected at that position in the month. Because the stem-and-branch cycle repeats every sixty days, a matching name supports a proposed date without identifying a unique date by itself.
Reference time matters when a calculated new moon falls close to midnight. The New Year new moon of 1916 is a useful boundary case:
| Reference time | Approximate new-moon time, with Gregorian date |
|---|---|
| Beijing local mean solar time, at 116°25′ east | February 3, 1916, at 23:51 |
| Mean solar time at 120° east | February 4, 1916, at 00:05 |
These are two time labels for the same astronomical event. The historical New Year followed the Beijing date, February 3. A calculation that assigns the event to a day using the other meridian places it on February 4. For a historical month start, the relevant question includes which day boundary the calendar used, not just the instant of the new moon.
Recording the result
A complete date note keeps the original wording beside the converted date and identifies the latter as Julian, Gregorian or proleptic Gregorian. Record the annual calendar, table or reconstruction used, including the edition or version. For software, retain the actual input and any calendar settings that affected the result.
A missing day should remain a month interval in the finished note. An uncertain leap marker may leave two possible months. Where a proposed reading or calendar reconstruction is still in doubt, identify that specific uncertainty alongside the result. This keeps a tentative reconstruction distinguishable from a fully identified date.