Shang Dynasty Lunisolar Calendar

By the 14th century BCE, the Shang Dynasty developed a lunisolar calendar, evidenced in oracle bone inscriptions found at Anyang. The system combined lunar months of approximately 29.5 days with a solar year of about 365.25 days, requiring intercalation to maintain seasonal alignment. The Shang used two methods: adding a 13th month at year's end or inserting an extra month between regular months. Their astronomical observations approximated lunar and solar cycles with accuracy comparable to modern calculations. This calendar system formed the foundation for subsequent Chinese calendars.