Faith · sources · inquiry

Calendars for careful study

Understand the nine calendar systems, compare dates and export a personal study event.

Project explanation

One date, several systems

Use a Gregorian date as a common starting point, then compare all nine browser converters: Gregorian, Persian/Shamsi, fixed Hebrew, civil Hijri, Ethiopian, Maya Long Count, Julian calendar, Julian Day and Modified Julian Day.

The labels and conventions matter. Hebrew months use Nisan as month 1 and include Adar II in leap years. Civil Hijri uses a tabular Friday epoch. The Persian converter uses a pinned astronomical boundary table. JD begins its integer count at noon; MJD uses a different origin and midnight boundary.

Project explanation

Plan study on your own calendar

The study planner creates an all-day event for a Gregorian date, with optional daily or weekly repetition. Download its .ics file and open or import it in a calendar application. The end date is exclusive, as required by the iCalendar format. Your event is created locally; downloading it does not send invitations or upload a schedule.

iCalendar specification, RFC 5545

Method limits

Calculated dates and observance

A date conversion does not determine a local sunset, crescent sighting or a community’s religious observance. Use the relevant local authority for those decisions. Historical labels may also differ from the proleptic mathematical calendars used here.

Calculation conventions and provenance · Explore lunar and seasonal cycles

Compare dates and plan study