At a glance
- Nature
- An added month, not a leap day
Definition and scope
An intercalary month adds an entire month rather than an extra day. Twelve lunar cycles are shorter than a solar year, so uncorrected month names would drift through the seasons. Intercalation repeats a month name with a leap label, demonstrating that the Chinese system coordinates both lunar and solar cycles.
Structure and details
Modern intercalation considers new moons, the eleventh month containing the winter solstice and major solar terms. When thirteen months occur in the relevant interval, the first month without a major term is designated intercalary. Do not detach the missing-term rule from its context. The leap month repeats the preceding month’s number.
Example and history
If a conversion table shows a fourth month followed by a leap fourth month, they are two successive lunar cycles. A birthday or family record must retain the leap label. Listing the ordinary month, leap month and next month shows how thirteen months fit into the year without implying that one physical day happens twice.
Contexts and limits
Intercalation is a calendar adjustment, not evidence of unusual personality or destiny. Festival repetition and leap-month birthdays depend on local or family conventions. Historical calculations can differ. Software and records should store leap status separately from the month number to avoid ambiguity when converting or comparing dates.
References & further reading
Historical sources document ideas and rules of their time, not empirical proof of predictive accuracy. Source notes identify the nature and scope of each reference.
- Hong Kong Observatory: The Chinese Agricultural CalendarInstitutional / reference source
Observatory explanation of lunar months, years and solar cycles, used for calendrical facts.
- Hong Kong Observatory: The 24 Solar TermsInstitutional / reference source
Solar-term definitions and the regional seasonal background of their names.
- Hong Kong Observatory: Gregorian–Lunar Calendar Conversion TableInstitutional / reference source
Official calendar conversion tables; users must preserve leap-month labels and time conventions.