Why do different cultures have different calendars?

The answer

Different calendars reflect different astronomical, religious, and cultural priorities. The Gregorian calendar (used globally for civil purposes) is solar-based, tracking Earth's orbit. The Islamic Hijri calendar is purely lunar, meaning its months shift through the seasons over a 33-year cycle. The Hebrew calendar is lunisolar, adding leap months to keep lunar months aligned with solar seasons. Ethiopia uses its own calendar derived from the ancient Coptic system and is roughly 7 to 8 years behind the Gregorian calendar. The traditional Chinese calendar is also lunisolar, and Hindu calendars vary by region. Iran's Solar Hijri calendar is considered one of the most astronomically accurate calendars ever devised. Each system anchors a community's festivals, agriculture, and sense of historical time.