lunarsolar

Lunarsolar refers to a calendar system that combines lunar months with a solar year, attempting to keep months aligned with the phases of the moon while maintaining the position of the Sun within the seasonal cycle. In a lunisolar calendar, months are typically based on lunar cycles, usually starting on or near new moons, and each month has 29 or 30 days. To prevent drift from the solar year and the seasons, intercalation—typically in the form of a leap month—occurs at intervals determined by traditional rules or astronomical observations.

Examples include the Chinese lunisolar calendar used for traditional festivals such as the Spring Festival; the Hebrew calendar, which uses a 19-year cycle with seven leap months to realign lunar months with the solar year; and various Hindu lunisolar calendars that insert extra months (adhik Maas) according to regional rules.

Intercalation is driven by solar terms and astronomical calculations; some calendars use the Metonic cycle (19 years with 7 leap months) as a rough approximation, while others employ more complex rules tied to lunar phase and the position of the Sun and the vernal equinox. The goal in all cases is to keep agricultural seasons and seasonal festivals in sync with the solar year while preserving the regular occurrence of lunar months.

Today, many nations use purely solar calendars for civil purposes, while lunisolar calendars remain important for religious, agricultural, and cultural events. Modern software and astronomical tables enable conversion between systems and help determine the dates of festivals and observances across different traditions.