20140919

Leap day

The autumnal equinox comes at MJD 56923.10331 (Tuesday, 2014-09-23 02:28:46 UT) in the Northern Hemisphere. Because that is 366 days after the previous one, the day before, 56922 (this Monday, Sept. 22), is a leap day in the French Republican Calendar. There are usually five complementary days at the end of the Republican year, sometimes collectively called Sansculottides, but this year there is a sixth complementary day, which is why the Republican leap year is called sextile. This day was called Fête de la révolution (Festival of the Revolution), commemorating the French Revolution.

Some people convert modern French Republican Calendar dates by using a rule like the Gregorian calendar, which usually has leap years every four years. This makes it easier to calculate, and is probably what the French would have eventually done, had they kept their calendar, but they did not. By this rule, 56922 (Mon., Sept. 22) is not leap day but actually New Year's Day, the first day of the month of Vendémiaire in the 223rd year of the Republic.

Leap day or New Year's Day, either way it's cause to celebrate!

Quartidi 4e jour complémentaire an CCXXII à 2 heures 95 minutes décimales t.m.P.
MJD 56920.289

20140830

Almanach national de France


I found a copies of the Almanach national de France on the Bibliothèque nationale de France web site. The edition for the second year of the Republican Calendar (l'an deuxieme), 1793-94, includes astronomical tables with decimal times. You can also see the times for the equinoxes and solstices and the phases of the moon written out.

For example, here is the Republican Calendar month of Nivose, in nouvelles heures, or "new times". It says
Solstice á 3 heures 20 minutes 64 secondes. HIVER.
Dernier Quartier á 5 h. 28 m.  Premier Quartier á 7 h. 10 m.
Nouvelle Lune á 9 h. 92 m.    Pleine Lune á 1 h. 53. min.
Hiver is winter. The phases (top to bottom then left to right) are last quarter, new moon, first quarter, full moon.

As I have pointed out before, I usually see decimal times today written with colons, although using colons was not common back then, but rather h and m. Using a decimal mark (which is the comma in French) would make more sense. Even today it is common in French to use h and m with standard time. Here you see a decimal time for the winter solstice written out in full with hours, minutes and seconds, corresponding to 3.2064 decimal hours, and the rest abbreviated, corresponding to 5.28, 9.92, 7.10 and 1.53 decimal hours.  Where there is room, minutes are abbreviated as min., or m. where there is not.

Therefore, I prefer using the old-style French notation, as shown here.

I can tell that most of the times are "true time", or local apparent solar time, which varies throughout the year in relation to mean time, and is shown by sundials. The last column shows when true solar noon occurs in local mean time. All times are relative to Paris.

Quartidi 14 Fructidor an CCXXII à 10 h. 84 m. t.m.P.
MJD 56900.077

Swatch on TLDR

The NPR program On the Media publishes a podcast and blog called TLDR, which is an Internet abbreviation for "too long; didn't read". On MJD 56896.7 (August 27) they re-released a podcast originally released on 56701.6 (February 13), which was about Swatch's Internet Time.  You can listen to the podcast and read the transcript.

@63
MJD 56900.021