Calendar & Holiday Information

Enter a date (CE only) and select the calendar system to discover corresponding dates in other calendar systems, day of the week, moon phase, and the next New/Full moon

Important: The Julian calendar day Thursday, 4 October 1582 was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 in most of Europe, but if you are looking at Russia the date after January 31, 1918 (Julian), became February 14, 1918 (Gregorian).

About This Tool

How It Works

This comprehensive calendar tool provides accurate conversions between different calendar systems and astronomical information:

  • Calendar System Selection: Choose whether your input date is Gregorian or Julian calendar (format: YYYY-MM-DD)
  • Gregorian Calendar: Shows the actual Gregorian date (if you entered Julian) or confirms your input
  • Julian Calendar: Shows the corresponding Julian calendar date using accurate historical conversion
  • The Gregorian/Julian conversion is powered by @the_hazzik/julian-gregorian-converter
  • Hijri Calendar: Shows the corresponding Islamic calendar date using lunar calculations. Powered by Aladhan API - Gregorian to Hijri (Islamic) calendar conversion.
  • Hebrew Calendar: Shows the corresponding Jewish calendar date using lunar-solar calculations. Powered by Hebcal API - Hebrew holidays and calendar data.
  • Day of Week: Calculated based on your selected calendar system (Gregorian or Julian)
  • Current Moon Phase: Shows the actual moon phase at midnight UTC on your selected date from three sources for comparison:
    • US Naval Observatory: Using US Naval Observatory API - available for dates between 1700-2100 only
    • PyMeeus: Using PyMeeus astronomical algorithms - available for all dates
    • DE441 (JPL): Using Skyfield with JPL DE441 ephemeris - covers dates from 13,200 B.C. to A.D. 17,191
    All sources include phase name and percentage illumination for comparison.
  • Next Moon Events: Shows upcoming New Moon and Full Moon times with 5-minute precision UTC timestamps. Uses Skyfield astronomical library with JPL DE441 ephemeris for all dates (covers 13,200 B.C. to A.D. 17,191). PyMeeus is used as a fallback only if DE441 is unavailable.

Additional Resources

For advanced calendar conversions and historical date calculations, visit Fourmilab's Calendar Converter, which provides comprehensive conversions between many calendar systems including Julian Day Numbers, Hebrew, Islamic, and more.

Religious Calendars: For comprehensive religious calendar information, see TrueCalendar which provides Orthodox, Catholic, Islamic, and other religious calendars.

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