Lifted straight from wiki, september 23rd.
Personally I like "Bisexuality Day" and "Christian Feast Day", a fun mix I think.* Autumnal equinox related observances (see September 22):
o Shubun no Hi (Japan)
o The second day of Mikeli (ancient Latvia)
* Celebrate Bisexuality Day (Bisexual community)
* Christian Feast Day
o Adomnan
o Padre Pio
o Thecla (Roman Catholic Church)
o September 23 (Eastern Orthodox liturgics).
* National Day (Saudi Arabia)
* Traditional New Year's Day in Constantinople and Eastern Orthodox Churches; because of the birthday of Augustus, not because of the equinox.