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Explanation

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What is this?

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This is an implementation of the Gregorian + calendar—which is the default civil calendar in most countries—with conversions to various other + calendars.

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Currently, it displays the following conversions for each day, if possible:

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How are BCE years handled?

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The astronomical convention is used, i.e. year 0 is 1 BCE, year -1 is 2 BCE, etc.

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Due to the way the common era (a.k.a. Anno Domini) year numbering system works, the year 1 BCE is + followed directly by 1 CE with no year zero. This makes math hard. As such, the astronomical convention + of making 1 BCE year 0 and extending this into the past was used.

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What is the JD (Julian day number) value?

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The integer Julian day (JD) number is the + continuous count of days since the beginning of the Julian period, which is very useful in astronomy and + in software for calculating durations without worrying about weird calendar issues. In this respect, + it's very similar to Unix time.

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JD 0 is assigned to the date Monday, January 1, 4713 BCE (Julian) or November 24, 4714 BCE (Gregorian). + More specifically, if fractional JDs are considered, then the integer value specifically refers to the + Universal Time noon on that date.

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What is the LC (Mesoamerican Long Count) date?

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The five (or more) numbers separated by dots is the corresponding + Mesoamerican Long Count + calendar date. This is commonly known as the “Mayan calendar.” This calendar is not + available for dates before August 11, 3114 BCE (Gregorian) or September 6, 3114 BCE (Julian).

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What is the FR (French Republican calendar) date?

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The French Republican + calendar was a calendar created and implemented during the French Revolution. It is also frequently + referred to as the French Revolutionary Calendar, but this is a misnomer: + year 1 of the calendar started on 22 September 1792, the day after the + abolition of the + monarchy and the founding of the French + First Republic.

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Specifically, the variant used here is the one I computed from + astronomy.

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