Historical Calendar Converter
Convert dates between Julian and Gregorian calendars for historical research
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📚 About Calendar Systems
The Julian calendar was introduced by Julius Caesar in 45 BCE and was used throughout Europe until 1582. The Gregorian calendar was introduced by Pope Gregory XIII in October 1582 to correct the Julian calendar's drift.
Why the change? The Julian calendar added one leap day every 4 years, resulting in an average year of 365.25 days. However, the actual solar year is 365.2422 days, causing the calendar to drift by about 11 minutes per year. By 1582, this had accumulated to 10 days of error.
Important: Different countries adopted the Gregorian calendar at different times. Britain and its colonies switched in 1752, Russia in 1918, and Greece in 1923. When researching historical dates, always verify which calendar was in use for that location and time period.
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Disclaimer: This calendar converter is provided for educational and research purposes. Historical date conversions can be complex due to regional adoption dates and calendar reforms. For critical historical research, please consult primary sources and specialized historical resources. Results are calculated using standard astronomical algorithms and may not reflect all local variations.