[prometheus76]

Where did you find their process for recalculating the dates? The Japanese calendar was lunar and calculated locally until the 1600s in some areas, all the way up to the 1800s in other areas. How did the researchers line up the dates in the journals to astronomical data? How can they assume that when a Japanese journal said "first day of spring" that they actually meant the astronomical first day of spring, for example? I'd like to see the methodology the researchers used, but I didn't find anything in their paper about it.

[Retric]

Astronomical events like eclipses get recorded and can be extrapolated backwards to precisely line up historic calendars. Similarly, major events like huge earthquakes can be correlated between different historic calendars.

Eventually you go back far enough and this breaks down, but we are talking recent history here.

[prometheus76]

You're assuming the researchers used earthquakes or astronomical events to correlate their date calculations, but they make no such claim. They do not explain their methodology for converting the historical calendar dates into Gregorian dates at all. Why should we give them the benefit of the doubt? They've included their dataset, but they haven't included their methodology for determining the Gregorian dates, yet their whole claim is that the dates are getting earlier and earlier. The line trending down also correlates with Japan converting to the Gregorian calendar in 1868. Why isn't that mentioned in their paper? If their methodology for converting historical dates is faulty or poor, that methodology could also account for the line appearing to move down starting in the mid-1800s.

They should be transparent about it and they weren't, and a lot of people here seem to be willing to just trust them and their methodology, but I can't figure out what's scientific or transparent about that. Isn't peer review supposed to catch and correct these types of issues before publication? And if not, shouldn't they be transparent enough in sharing their methodology that the concerns raised by amateur idiots like myself would be easily addressed, or at least accounted for?

[Retric]

These are hardly the first researches to want to correlate Japan’s dates with the Gregorian calendar. If you think the historic record is so wrong then feel free to do some original research and prove it, but don’t assume people are idiots.

Anyway, you have clearly already decided the issue in your own mind and are looking to justify it. So, no I am not going to waste my time providing evidence you can look up if you’re willing to consider the possibility you’re wrong then dare to do it yourself.

[prometheus76]

I feel the exact same way. They didn't share their methodology, and their claims hinge on the methodology they used for converting the dates. I'm not accusing them of anything. I'm asking to see their methodology. You are the one who is giving them the benefit of the doubt and assuming they did it correctly, which is antithetical to peer-reviewed science.

[Retric]

They didn’t need to do the correlation, other people have already done the leg work.

You’re effectively complaining they didn’t show their work when using dates from the Roman etc calendar. Historians really care about getting dates correct and have done extensive work to line up each historical calendar where possible.

[luming]

https://www.jstage.jst.go.jp/article/timestudies/1/0/1_17/_a...

This is the paper. It did describe the challenges of inferring the full-bloom date from old literary work. But the calendar conversion is not one of the challenges.

[prometheus76]

By everything I've read, it should be included as a challenge, and they should be explicit about the method they used to determine the Gregorian dates, because it's not straightforward, nor is there even an agreed-upon method or table to use for conversion, yet their whole claim rests on the verifiability of the dates.

[luming]

https://rnavi.ndl.go.jp/research_guide/entry/theme-honbun-40...

This is a list of material and conversion tables composed by the National Diet Library on the old calendars. There are clearly well-established method and researches about this. This would be the most basic problem for anyone studying history in Japan. It may be not straightforward (for you), but it certainly would be too generic and elementary for other historians to read in a paper like this.

[prometheus76]

If this is what they used, why didn't they say that? I'm not making a claim about what method they used. I'm saying that whatever method they used is prone to error and should be included in the methodology of the paper. What is wrong with being transparent about their methodology? And what is wrong with expecting that level of transparency in a scientific paper making a specific claim?

[prometheus76]

I have to admit, the passive-aggressive ad hominem attacks caught me by surprise, but my request for transparency with regard to the methodology they employed when converting their dates stands.

[bgee]

> The Japanese calendar was lunar and calculated locally until the 1600s in some areas

Isn't the Japanese calendar Lunisolar and borrowed from China? (from the wikipedia link you posted above)

[prometheus76]

"After that, Japan calculated its calendar using various Chinese calendar procedures" also from the wikipedia article. This is all just illustrating my point further.