2023-04-22 19:02:25 -04:00
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2023-04-22 23:26:07 -04:00
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content="An interactive version of the Julian calendar, extended indefinitely into the future."/>
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2023-04-22 19:02:25 -04:00
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2023-04-22 23:26:07 -04:00
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2023-04-22 23:26:07 -04:00
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content="An interactive version of the Julian calendar, extended indefinitely into the future."/>
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2023-04-22 19:02:25 -04:00
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2023-04-22 23:26:07 -04:00
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<meta property="og:image:alt" content="A calendar icon that displays the date March 15th (Ides of March)."/>
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2023-04-22 19:02:25 -04:00
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<title>Julian Calendar (extended indefinitely to the future)</title>
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<a class="navbar-brand" href="#">Julian Calendar</a>
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<li class="nav-item">
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<a class="nav-link" href="#explanation">Explanation</a>
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<li class="nav-item">
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<a class="nav-link" href="https://frcal.qt.ax">French Republican Calendar</a>
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<noscript>You need to enable JavaScript to run this app.</noscript>
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<div id="root"></div>
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<div class="main">
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<h2 id="explanation">Explanation</h2>
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<div class="card">
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<div class="card-body">
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<h4 class="card-title">What is this?</h4>
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<p class="lead">The <a href="https://en.wikipedia.org/wiki/Julian_calendar">Julian
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calendar</a> is a calendar introduced by Julius Caesar in 46 BC. A reformed version, the <a
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href="https://en.wikipedia.org/wiki/Gregorian_calendar">Gregorian
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calendar</a>, forms the basis of civil calendar in most countries.</p>
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<p>Julius Caesar (with aid of Sosigenes of Alexandria) introduced this calendar to replace the earlier Roman
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2023-04-23 20:27:52 -04:00
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calendar, which required manual addition of leap months to keep it in synchrony with the seasons.
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Unfortunately, it had leap days every four years without question, resulting in the average year
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2023-04-22 19:02:25 -04:00
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having 365.25 days. However, the actual tropical year is roughly 365.2422 days, resulting in the Julian
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calendar gaining a day every 129 years. This means that seasons drift, starting earlier and earlier in
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the year.</p>
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<p>In 1582, Pope Gregory XIII decided to fix this drift by reducing the number of leap days, motivated by a
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desire to keep the March equinox on March 21st, since that value was hardcoded in the calculation for
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the date of Easter. To achieve this, he made years divisible by 100 but not by 400 non-leap years,
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resulting in 97 leap years every 400 years, resulting in the Gregorian calendar. To bring the equinox
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back in alignment, October 5th to October 14th in 1582 were deleted. The result is the Gregorian
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calendar.</p>
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<p>This website extends the Julian calendar indefinitely into the future for reference reasons. Note that in
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the 20th and 21st centuries, the Julian calendar is 13 days behind the Gregorian calendar.</p>
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</div>
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</div>
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<div class="card">
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<div class="card-body">
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<h4 class="card-title">How are BCE years handled?</h4>
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<p class="lead">The astronomical convention is used, i.e. year 0 is 1 BCE, year -1 is 2 BCE, etc.</p>
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<p>Due to the way the common era (a.k.a. Anno Domini) year numbering system works, the year 1 BCE is
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followed directly by 1 CE with no year zero. This makes math hard. As such, the astronomical convention
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of making 1 BCE year 0 and extending this into the past was used.</p>
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</div>
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</div>
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<div class="card">
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<div class="card-body">
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<h4 class="card-title">What is the JD (Julian day number) value?</h4>
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<p>The integer <a href="https://en.wikipedia.org/wiki/Julian_day">Julian day (JD) number</a> is the
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continuous count of days since the beginning of the Julian period, which is very useful in astronomy and
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in software for calculating durations without worrying about weird calendar issues. In this respect,
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it's very similar to Unix time.</p>
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<p>JD 0 is assigned to the date Monday, January 1, 4713 BCE (Julian) or November 24, 4714 BCE (Gregorian).
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More specifically, if fractional JDs are considered, then the integer value specifically refers to the
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Universal Time noon on that date.</p>
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</div>
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</div>
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<div class="card">
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<div class="card-body">
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<h4 class="card-title">What is the LC (Mesoamerican Long Count) date?</h4>
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<p>The five (or more) numbers separated by dots is the corresponding
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<a href="https://en.wikipedia.org/wiki/Mesoamerican_Long_Count_calendar">Mesoamerican Long Count
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calendar</a> date. This is commonly known as the “Mayan calendar.” This calendar is not
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available for dates before August 11, 3114 BCE (Gregorian) or September 6, 3114 BCE (Julian).</p>
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</div>
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</div>
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<div class="card">
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<div class="card-body">
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<h4 class="card-title">What is the FR (French Republican calendar) date?</h4>
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<p>The <a href="https://en.wikipedia.org/wiki/French_Republican_calendar">French Republican
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calendar</a> was a calendar created and implemented during the French Revolution. It is also frequently
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referred to as the <em>French Revolutionary Calendar</em>, but this is a misnomer:
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year 1 of the calendar started on 22 September 1792, the day after the
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<a href="https://en.wikipedia.org/wiki/Proclamation_of_the_abolition_of_the_monarchy">abolition of the
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monarchy</a> and the founding of the <a href="https://en.wikipedia.org/wiki/French_First_Republic">French
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First Republic</a>.</p>
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<p>Specifically, the variant used here is <a href="https://frcal.qt.ax/">the one I computed from
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astronomy</a>.</p>
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<p class="text-muted">Copyright © 2022<%= new Date().getFullYear() > 2022 ? `–${new Date().getFullYear()}`
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: '' %>
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<a href="https://quantum5.ca">Quantum</a>.
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Licensed under <a href="https://www.gnu.org/licenses/agpl-3.0.en.html">GNU AGPLv3</a>.
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Source code available on <a href="https://github.com/quantum5/frcal">GitHub</a>.<br>
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