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There is something about this article that kind of annoys me. It's my understanding that back in the year 1006, the entire world was not using the same calendar. Each of these observations would not have been recorded as simply "May 1, 1006", they would have been in each observer's respective calendar... Yet this article just states them as being recorded on the same day using the Julian/Gregorian calendar format that we use today. I would have liked the article to go into more detail about how they were able to sync up the dates across the various calendar systems.

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This is Wikipedia. If you possess the knowledge about local calendars of the time, go on and improve the article.

For astronomical research, it's easiest when events are dated using one calendar to correlate the observations across the whole planet. No matter which calendar specifically, it just must be uniform. For cultural research, it's more important to use a local calendar and e.g. see how the supernova was related to other culturally significant events.

Also, an article written in English is bound to use the Gregorian or Julian calendar which is familiar to the readers. An article written in Arabic, or Hebrew, or Tamil, or Malay may use the respective different calendars instead, as familiar to the readers.

> An article written in Arabic, or Hebrew, or Tamil, or Malay may use the respective different calendars instead, as familiar to the readers.

Extrapolating from the only example I know, I wouldn't bet on it.

Before moving to Israel I knew that Rosh HaShanah (Hebrew New Year) is a public holiday and Gregorian New Year isn't, so I expected Hebrew calendar to be somewhat visible in everyday life or at least in official documents. Turns out, with the exception of holidays — to some surprise, including the decidedly secular Independence Day — it really isn't, everyone uses Gregorian.

This is somehow expected when we talk about modern Israel. Maybe it would be less so when describing events of 1006 AD, if descried by contemporaneous Jewish sources.

Again, this a difference between astronomy and history points of view. In natural sciences, one would expect the now-universal units that originated in Western science: Julian calendar, SI units, times in UTC, etc. In historical and otherwise localized studies, I would expect a local / period-salient calendar, local units as reflected in the period's documents, etc. Converting these into exact modern dates and units is sometimes hard, and subject to a debate among historians.

The article on SN 1054 (the supernova that formed the Crab Nebula) goes into a lot more detail about how the historical accounts were correlated.

https://en.wikipedia.org/wiki/SN_1054

In 1006, the entire Christian world would have been using the Julian calendar (Gregorian isn't invented until 1582), although there is some variance on when different countries recognized the new year in the Julian calendar. Albeit, May is one of those months where everyone agreed on the year.

Outside of the Christian world, the correlations between different calendars and the Julian calendar is quite well-known, because by the time Europeans contacted people following those calendars, they can ask "what day is today" and get the Gregorian-Julian-local calendar correspondence. If you've got a stable year count (not based on reigning kings), it's easy to work out older dates. If you have regnal year numbering, and you have enough written evidence that you can decisively determine how long each king reigns for, then you can also carry that over to a complete calendrical determination.

In cases where the calendar is no longer used, you can match up calendars by looking for records corresponding to known (largely astronomical) phenomena (eclipses are particularly helpful) and get correlates that way. This is how we match the Mesoamerican Long Count to the Julian/Gregorian calendar.

Evidently the various calendar systems have been ‘harmonised’ in such a manner that (I presume) according to our calendar it would’ve been on the 1st May 1006, which I take literally to mean something along the lines of “May 1st 2023 was the 1017th annual anniversary of the event”.

Hmm, but this is a very common problem particularly in history and archaeology and one that requires highly specialized expertise. Therefore almost always a modern unified calendar is used in new publications and the problem of dealing with historical dates as written is left to specialists. I don't think every article about per-modern events and events outside Gregorian-based calendar usage should mention that.

> It's my understanding that back in the year 1006, the entire world was not using the same calendar. Each of these observations would not have been recorded as simply "May 1, 1006"

That is correct, but what would that help anyone in general (for any historic reporting)? We give dates on our agreed today's scale.. as we usually would also give other measurements like masses or lengths in our scale, unless explicitly given with other earlier units?

Even today in the news you will usually hear "an earthquake happened tonite at 2am in far away land" (and only eventually added, but then explicitly the local time).

Especially for this event I wonder, how many different calendars would you want to had mentioned to be satisfied? :)

> That is correct, but what would that help anyone in general (for any historic reporting)?

The question is rather what are the error bars with these observations. When someone says "my car broke down last week" everyone understand that that is not a precise timestamp. On the other hand if you hear "according to the telemetry the crankshaft seized at 1696606533 unix timestamp." you know that they are talking about a very precise moment in time.

The problem comes if you take the first kind of description and convert it to a unix timestamp you imply precision where there was none found originally.

So when the wikipedia entry says "According to Songshi, the official history of the Song Dynasty (sections 56 and 461), the star seen on May 1, 1006, appeared to the south of constellation Di, between Lupus and Centaurus." Do they mean that Songshi wrote down the date according to his local convention which can be converted with a high confidence to our current date system as "May 1, 1006"? Or did they just erroneously implied more accuracy than what they have?

I think the calendar problem is an entirely different subject that would warrant it's own article. I suppose what you could do is look up the calendar for each historical report of the event and then convert it to a single calendar. https://en.wikipedia.org/wiki/List_of_calendars

If the article is twice as long, I'd say it definitely should have more details about each local reports, including dates in their corresponding calendars.

But at current length? I think that detail would not be necessary and even kinda distracting in term of briefness. It's not really of great importance for the event itself anyway.

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