I was looking for information about la fête de la raison, the Day of Reason, or Festival of Reason, which Wikipedia says was another name for one of the complementary days, or Sansculotides, in the French Republican Calendar, Opinion Day, which falls on 20 September (MJD 55459) this year. However, I cannot find an original source for this, and the Wikipedia article on the Cult of Reason and other sources state that it was instead held once, on 20 Brumaire, Year II (10 November 1793, JD 2376253/4), and the organizers were guillotined a few months later.
There is also a US National Day of Reason on the first Thursday of May, which is unrelated, but really cool.
BTW, shana tova 5771 and Eid Saeed!
Tridi 23 Fructidor an CCXVIII à 4hd 42md t.m.P.
1 Tishrei 5771
30 Ramadan 1431