Sep 23, 1846
The German astronomer Johann Gottfried Galle discovered Neptune（海王星）, the eighth planet orbiting around the Sun.
Reference
https://www.nasa.gov/feature/175-years-ago-astronomers-discover-neptune-the-eighth-planet
Today is
International Day of Sign Languages
Reference
https://www.un.org/en/observances/sign-languages-day
Sep 23, 1939
Sigmund Freud, the Austrian neurologist and the founder of psychoanalysis, died at age 83 (by euthanasia.)