Walking Back From 1600 With Dated Coins

Well my head is officially about to implode. After reading all about the various calendars.... Roman, Alexandrian, Ancient Macedonian, Coligny, Asian, Julian, Gregorian. Hijri (Solar, Tabulated, Luna) ad infinitum, I don't see a way to "accurately" convert from one to another .
Perhaps a table of conversions that is mutually acceptable could be formulated and made part of this thread (and the HFBCWG threads) for reference. Or perhaps if an AH year is so close to having a foot in each camp (C.E. year), that it be acceptable for either (but not both) of the C.E. years.

I'm just glad it's not my decision

1437 Cologne Groschen:

Beautiful coins! Especially that gold!
(I love how the lettering puts abbreviation apostrophes everywhere - most coin types with abbreviated legends never bother with that kind of thing)

As a reminder, today is supposed to be 1436 day; I don't count the year for the ongoing day as missing because there could still be right-day coins posted later in the day. So now that 1437 had been posted we're back down to seven missing years for now.

Nice examples, Spence!

This is exactly the rule I've been using all along (though I hadn't thought of the 354 day problem, it being such an extreme edge case - thanks for bringing it up!), and the current confusion is (merely) over whether we use the Julian or Gregorian definition for the CE year, especially for dates prior to 1582 CE where technically the Gregorian calendar hadn't existed at the time.

(It turns out that every CE year between 700 and 1500 [and probably some way later than that; I hadn't checked where exactly this ends] unambiguously corresponds by this rule to at least one AH year, even if we're unsure about the Julian/Gregorian choice, which means that it would be theoretically possible to cover that range using only AH dates; however, there are sometimes intermediate AH years where the assignment depends on which way we go. 841 AH is one of those.
I think for post-1752 dates it would be reasonable to default to Gregorian. I can try to check if there's any year between 1500 and 1752 CE that doesn't have an unambiguous conversion.)

There is a bit of an extra confusion because @ttkoo apparently misinterpreted the rule as claiming that an AH year converts to whichever CE year it is the majority of, and sometimes you get an AH year such that (say) 180 days of it are in one CE year and 175 are in another, such that it technically isn't the majority of either. (Usually this is the case for only one of Julian and Gregorian, but as we get deeper into the dates it can start to happen for both at once.)

As for 834 AH, there is no ambiguity here: in both the Julian and Gregorian versions, that year starts in September 1430 CE and ends in September 1431 CE, such that the majority is clearly in 1431. I'm not sure where you got 1432 from; no part of 834 AH lands in that year.


Current list of missing years: 1464, 1463, 1462, 1461, 1457, 1454, 1446, 1437, 1436. We're still hanging on at just above 95% coverage since 1600, though if 1435 also doesn't show up we would (again) cross that number.

1633. Maybe. It depends on the converter.

The difference between Julian and Gregorian is 10 days in 1633.

According to date-converter.com, 1 Rajab 1042 AH is 11 January 1633 CE Gregorian = 1 January 1633 Julian (which makes 1042 AH in Julian an exactly evenly split year), while 1 Rajab 1043 AH is 31 December 1633 Gregorian = 21 December 1633 Julian (which puts 1043 AH in Gregorian on the side of 1633 by one day).
Meanwhile, according to habibur.com, 1 Rajab 1042 AH is 12 January 1633 Gregorian = 2 January 1633 Julian (which puts 1042 AH in Julian on the side of 1633 by one day), while 1 Rajab 1043 AH is 1 January 1364 Gregorian = 22 December 1633 Julian (which makes 1043 AH in Gregorian an exactly evenly split year).

This means that for each specific converter there's an AH year that corresponds to 1633 CE in both Julian and Gregorian, but which year that is varies between the converters.


[Looking it up: the 1-day divergence between the two converters apparently goes right back to divergences in the epoch, and we probably want the one in Habibur, which is a day later. This page goes into some detail.
OTOH I don't know where does Habibur get the month lengths from; they seem weirdly uneven. Maybe we should just subtract a day from the DateConverter results instead.
Alternately, use the big converter - though its date-choosing method is somewhat cumbersome - and choose mode IIc as likely the most reasonable one for coin date conversion purposes.

I do still want to figure out whether there is such an example within a single date converter. Not for the next two days, though.]

Very nice!