Starship Asterisk*

Chris Peterson wrote:

neufer wrote:I now think that SN 1054 (M1: The Crab Nebula) at ~7,000 years ago [= 954 years + 6,000 (light-)years] was the last known supernova to occur.

How about SN 185, at ~4800 years (1823 years ago + ly distant)?

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<<SN 393 is the name of an event considered as probable a Supernova having been observed in the year 393 by Astronome S Chinese. The observation of this event had been catalogued according to the habit of the time under the name of “invited star”.

Historical testimonys

Two historical sources mention this invited star: the Jinshu and the Songshu . Those make a nearly identical account of the phenomenon and result probably from the same source, now disappeared. The astronomical part of the testimony (which according to the habits of the time was always accompanied by its astrological interpretation ) indicates:

“In 18th year of the Taiyuan period of the reign of the emperor Xiaowu, at the time of the second lunar month, a star invited appeared in Wei. It remained until the ninth lunar month, where it is extinct. ”

The chronology of the Chinese world makes it possible to date precisely this testimony at the year 393, the second month lunar corresponding to the period being spread out February 27th with the March 28th, and the ninth month of the October 22nd to the November 19th. The reason length of the interval between the second and the ninth month comes from the addition this year there of an intercalated month to the lunisolar Calendrier into force in the Chinese empire. The objective was to compensate for the shift of calendar which would only cause of the twelve months lunar years (correspondent at one duration lower than the 365,25 days, to see Chinese Astronomie).

Interpretation

In the most unfavourable case, the invited star remained visible of at the end of March at the end of October, that is to say more than 200 days. That invalidates the assumption that this event corresponded to a Comet. The distinction between a Nova and a Supernova, only other possible explanations of an event of invited the star type, is more difficult to establish. Testimony mentions that the event occurred in Wei. Wei corresponds here in the name of a lunar Loge, i.e. a band of Right ascension, and a Astérisme located in the Constellation of the Scorpion, corresponding to the tail of the animal according to the Western constellation division. If testimony refers to the lunar cabin, the galactic Latitude is not specified, and the event has few chances to be itself produced in the galactic Plan. In such a case, it would not be possible to associate the event with a supernova. If testimony refers to the asterism associated with the lunar cabin, then, this one being exactly in the galactic plane, an interpretation of the supernova type is largely more probable. The only indication making it possible to take a decision between these two assumption is the term in (“ zhong ”), which strongly suggests that one speaks about the asterism, whose stars form a convex polygon.

A problem with the interpretation of the asterism comes from what at the time of the ninth lunar month, the proximity of the Sun returned the observation of this area of the impossible sky. Except imagining that the star was very brilliant, in which case the proximity of the Sun did not prevent its observation, the period of the ninth month as time of last visibility is not easily possible. It should however be noted that the one month errors are not rare in the reports of observations of the time (as attested by the study of the mentions of the planetary conjunctions which can be dated precisely). On the assumption that the month of last visibility is in fact the eighth month lunar, it is possible to make coherent the whole of the testimony, which strongly suggests an interpretation of supernova.

Identification of the remanent one

The area of the asterism Wei , near to the galactic Center, is very rich in remanent of supernova. Even by keeping only the remanent ones which has all the characteristics of remanent young people, there remain two remanent possible, SNR G348.5+00.1 and SNR G348.7+00.3. The two remanent ones are estimated to be at a distance from 10,2 ± 3,5 kpc, deduced from the measurement of the absorption of the neutral Hydrogène. This measurement of distance, combined with the angular Size of these objects and at their speed of typical expansion (lower or equalizes with 10 000 km/S, to see Remanent supernova). can be made compatible with the age of the supernova if one considers the low fork of the estimate of distance. This fork bases of distance is in any event made necessary to explain the observation with the naked eye of such events. Another assumption, suggested by Z.R. Wang, is that the remanent one is in fact SNR G347.3-00.5 (also named X-ray J1713.7-3946). To reconcile its angular size with the age of remanent, it would be necessary that this one is located at a distance from 1,1 kpc. Other authors however point out that this remanent could be associated with a Région HII and molecular clouds, whose distance is estimated at 6 kpc, returning in this case the association of remanent with this event because its real size would be then too large. In any event, the identification of remanent is impossible today because of the big number of candidates and uncertainties in their measurements of distance. The nature of supernova of this event seems on the other hand much more firmly established, although not some in the absence of one only and single candidate of remanent. >>
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neufer wrote:SN 185 is about 8,200 light-years away.

What you probably mean is SN 393...

Chris Peterson wrote:But the reality is, figuring out the distance to most objects inside our galaxy (unless they are very close) is difficult, and most published distances have high uncertainties. So who really knows? Of course, that's one reason why scientists don't generally bother to assign local supernovas to any kind of common time reference frame. Scientifically, all that matters is when they are observed. (That's different for supernovas at cosmological distances, but in that case redshift is used, not distance as such.)