2022-02-12 09:44:58 -05:00
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2022-02-12 21:16:00 -05:00
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<meta name="description" content="Interactive French Republican Calendar (a.k.a. French Revolutionary Calendar)."/>
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<title>French Republican Calendar (a.k.a. French Revolutionary Calendar)</title>
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<a class="navbar-brand" href="#">French Republican Calendar</a>
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2022-02-12 09:44:58 -05:00
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2022-02-12 21:16:00 -05:00
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<li class="nav-item">
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<a class="nav-link" href="#explanation">Explanation</a>
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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/French_Republican_calendar">French Republican
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calendar</a> was a calendar created and implemented during the French Revolution.</p>
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<p>It was also frequently known as the <em>French Republican Calendar</em>, but this was a misnomer: year 1
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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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</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 does it work?</h4>
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<p class="lead">A year consists of 12 months of 30 days each, divided into three <em>décades</em> of 10 days
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each, followed by 5 complementary days (6 in leap years).</p>
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<p>The year starts on the day of the autumnal equinox at the Paris Observatory (longitude 2°20′14.03″ E). A
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leap year follow directly from this definition: a year is a leap year when the next autumnal equinox
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happens 366 days later instead of the normal 365. By this definition, the year will <b>never</b> drift
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with respect to the seasons.</p>
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<p>The 12 months are: <em>Vendémiaire</em>, <em>Brumaire</em>, <em>Frimaire</em>, <em>Nivôse</em>, <em>Pluviôse</em>,
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<em>Ventôse</em>, <em>Germinal</em>, <em>Floréal</em>, <em>Prairial</em>, <em>Messidor</em>, <em>Thermidor</em>,
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<em>Fructidor.</em></p>
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<p>The complementary days are: <em>la Fête de la Vertu</em>, <em>la Fête du Génie</em>, <em>la Fête du
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Travail</em>, <em>la Fête de l'Opinion</em>, <em>la Fête des Récompenses,</em> and <em>la Fête de la
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Révolution</em> (leap years only).</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's so special about this version?</h4>
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<p class="lead">Most versions of the calendar floating around doesn't use the original definition above.</p>
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<p>Most versions uses the so-called <em>Romme</em> method for leap years, using the same leap year rules as
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the Gregorian calendar, i.e. every year divisible by four, except century years not divisible by 400.
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This method might make sense, except years 3, 7, and 11 were leap years under the original rules and
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were observed as such in real life, but the <em>Romme</em> method instead makes years 4, 8, 12 leap
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years instead.</p>
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<p>This version uses the original rules. The <a href="https://ssd.jpl.nasa.gov/planets/eph_export.html">JPL's
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DE440 and DE441 ephemerides</a> were used to calculate the exact timings of the autumnal equinoxes
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between the Gregorian years 13201 BCE and 17191 CE (corresponding to the French Republican years -14991
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to 15399). The times were then converted to UT1+00:09:21, the exact local time at the Paris Observatory.
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UT1 was chosen to keep track of the Earth's rotation without having to worry about the issues posed by
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leap seconds in UTC. Note that due to the uncertainty over
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<a href="https://en.wikipedia.org/wiki/%CE%94T_(timekeeping)">ΔT</a> — the difference between UT1 and
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Terrestrial Time (TT) used in the ephemerides — it is theoretically possible for there to be
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inaccuracies when the equinox occurs very close to midnight.</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 are those numbers below the Gregorian 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 (25 Thermidor -4905).</p>
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</div>
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<footer class="footer">
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<div class="container">
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<p class="text-muted">Copyright © 2018-<%= new Date().getFullYear() %> <a href="https://quantum5.ca">Quantum</a>.
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Licensed under
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<a href="https://www.gnu.org/licenses/agpl-3.0.en.html">GNU AGPLv3</a>. Source code available on
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<a href="https://github.com/quantum5/frcal">GitHub</a>.<br>
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2022-02-12 09:44:58 -05:00
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