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I think it's not as hard as it initially seems. Lunar calendars are based on the shape of the moon, and we can compute past phases of the moon with sufficient

I think it's not as hard as it initially seems. Lunar calendars are based on the shape of the moon, and we can compute past phases of the moon with sufficient accuracy. So, if the record said "cherry blossoms peaked at the tenth day of the second month, year X", then the only remaining question is when the "second month" started. Each lunar month is 29 or 30 days long, so if we miscalculate the month then the error will be also 29/30 days, back or forth. However, the graph in the article shows that almost all dates fall in (modern calendar) April. So, if the blossoms peaked at 4/20 and we miscalculate by one month, we'll arrive at 3/21 or 3/22, which is too early to be likely. Ditto in the other direction. So, even in the worst case, we can safely assume that most of the dates shown are correct (or maybe one day off, due to disagreement over when the new moon started). In addition, if they were meticulous enough to record cherry blossoms, I'd assume that the Japanese Imperial court would have written how many months were in each year ...

prometheus76 6y ago
Please see my other comment. I did further research and the problem comes because of drift. The lunar calendar would drift away from astronomical events, and this was a known problem, so they would occasionally add a 13th month to a year, but it wasn't done systematically. Also, there have been several attempts among scholars to create conversion tables for dates, and each of them have errors, sometimes up to 4 weeks. So which table did the researchers use? We don't know. And all of the conversion tables have errors, which brings me to my original point: making a claim that "this year is the earliest day of blossoming since the 800s in Japan" is scientifically unverifiable, because we cannot link historical calendar dates to current gregorian dates accurately before 1863, when Japan converted to the gregorian calendar.
- labawi 6y ago
  We do not need a generalized date mapping function to verify the claim, we only need to verify specific events/dates, and even for those we only need to verify a single inequality. OTOH, looking at the data, events are dispersed over more than a month (range 124 - 86 = 38 days), so it is possible an earlier date was pushed later, where it fits better - one cannot reliably deduce month from year + day of month.

prometheus76 6y ago

Please see my other comment. I did further research and the problem comes because of drift. The lunar calendar would drift away from astronomical events, and this was a known problem, so they would occasionally add a 13th month to a year, but it wasn't done systematically. Also, there have been several attempts among scholars to create conversion tables for dates, and each of them have errors, sometimes up to 4 weeks. So which table did the researchers use? We don't know. And all of the conversion tables have errors, which brings me to my original point: making a claim that "this year is the earliest day of blossoming since the 800s in Japan" is scientifically unverifiable, because we cannot link historical calendar dates to current gregorian dates accurately before 1863, when Japan converted to the gregorian calendar.

labawi 6y ago
We do not need a generalized date mapping function to verify the claim, we only need to verify specific events/dates, and even for those we only need to verify a single inequality. OTOH, looking at the data, events are dispersed over more than a month (range 124 - 86 = 38 days), so it is possible an earlier date was pushed later, where it fits better - one cannot reliably deduce month from year + day of month.