Discovery of S Andromedae, first extragalactic supernova observed

Background. SN 1885A was a supernova in the Andromeda Galaxy, the only one seen in that galaxy by astronomers. It was the first supernova ever seen outside the Milky Way, though its extragalactic nature was not appreciated at the time due to its distance. At the time, it was called "Nova 1885" because the distinction between novae and supernovae was not yet known.

Observations. The supernova was first seen on August 17, 1885, by French astronomer Ludovic Gully. Irish amateur Isaac Ward claimed to see it on August 19, 1885, but did not publish immediately. Ernst Hartwig independently detected it on August 20, 1885, at Dorpat Observatory, communicating this via telegram on August 31, 1885, after verifying it was not reflected moonlight.

Impact. Hartwig's telegram prompted widespread observations and the publication of earlier reports by Gully and Ward. The event reached magnitude 5.85 on August 21, 1885, and faded to magnitude 14 six months later. This observation marked the first time a supernova was studied in a galaxy other than the Milky Way.