SN 1885A

Supernova 1885
Observation data (Epoch J2000.0)
Supernova type	Ia
Remnant type	Unknown
Host galaxy	Andromeda Galaxy
Constellation	Andromeda
Right ascension	00h 42m 43.11s
Declination	+41° 16′ 04.2′′
Galactic coordinates	121.1702 -21.5741
Discovery date	20 August 1885 UTC
Peak magnitude (V)	+6
Distance	2.6 Mly
Physical characteristics
Progenitor	Unknown
Progenitor type	Unknown
Colour (B-V)	+1.3 ~ +0.6
Notable features	First and only supernova observed in Andromeda; first extragalactic supernova observed; closest Type Ia observed

Supernova 1885

Other designations
SN 1885A, CXOM31 J004243.0+411603, S Andromedae, S And, BD+40° 147a, 2MASS J00424312+4116032, AAVSO 0037+40, CXOM31 J004243.1+411604, RJC99 Sep-95.
Database References
Simbad	Data
	Image

SN 1885A (also S Andromedae) was a supernova in the Andromeda Galaxy, the only one seen in that galaxy so far by astronomers, and the first ever noted outside the Milky Way. It is also known as "Supernova 1885".

Discovery

Isaac Ward

It appears to have been seen first on August 17, 1885, by French astronomer Ludovic Gully during a public star gazing event, although Gully at that time thought it was scattered moonlight in his telescope and did not follow up on this observation. Irish amateur astronomer Isaac Ward in Belfast claimed to have seen the object on August 19, 1885, but did not immediately publish its existence.

The independent detection of the supernova by Ernst Hartwig at Dorpat (Tartu) Observatory in Estonia on August 20, 1885, however, was communicated in a telegram on August 31, 1885, once Hartwig had verified in more ideal circumstances that the feature was not caused by reflected moonlight. The telegram prompted widespread observations of the event, and prompted Isaac Ward, Ludovic Gully, and several others to publish their earlier observations (the first reports on S And appeared before Hartwig's discovery letter which followed his telegram, since the letter was initially lost by Astronomische Nachrichten and only reprinted in a later issue). The history of the discovery is summarized by K.G. Jones and de Vaucouleurs and Corwin. Both studies doubt that Ward really saw the event since his estimated magnitude is significantly off from the later reconstructed lightcurve and conclude that Hartwig should be considered as the discoverer of the Supernova.

Features

SN 1885A reached magnitude 5.85 on 21 August 1885 and faded to magnitude 14 half a year later. The star was reported to be reddish in color and declined very rapidly in brightness, which is atypical for Type Ia supernovae. Some astronomers observed the spectrum of the star visually (no photographic spectral observations were made in that time). These observations were made at the limit of visibility, but they are in good agreement with each other and with modern data on typical supernovae of Type Ia. They are strong evidence for the assignment of this star to this type.

The location of the supernova event was 16″ from the relatively bright nucleus of the galaxy. This made detection of the supernova remnant difficult, and multiple attempts proved unsuccessful. Finally, in 1988, R. A. Fesen and others using the 4-meter Mayall telescope at Kitt Peak discovered the iron-rich remnant of the explosion. Further observations were made with the Hubble Space Telescope in 1999.

The importance of observing the Andromeda S supernova is that, by comparing its magnitude to records of nearby supernovae, astronomers found it to be at least 750,000 light-years distant (later revised to 2,200,000); and that M31 was not a gas or dust cloud, but an "island universe" or galaxy.

See also

• List of Andromeda's satellite galaxies