at the height of the Church’s calendar problem, in the second half of the 16th century, the eastern Church and the western Church were an incredible ten days out of sync with one another. This was only reconciled in 1582 when Pope Gregory XIII implemented what has become known as the Gregorian calendar reform.
This doesn't sound right at all. Why would the church calendars be out of sync at the time? In fact, it was the Gregorian reform that put them out of sync. They are still out of sync and the gap is growing.
Bonus history trivia question: What month did the Russian October Revolution happen?
Seriously, what planet is this guy from? My family is Eastern Orthodox and this year we have Easter on the same day as the Westerners (Catholics and Protestants). It's a big deal because this very rarely happens. Sometimes we're as much as month or more apart from one another. Nothing has been resolved on the calendar issue between east and west.
This depends on the particular church. I know that Serbian Orthodox and Russian still officially use the Julian calendar. AFAIK the most of other Orthodox churches like Greek, Romanian, etc. have switched to the Gregorian calendar, e.g. they celebrate Christmas on Dec the 25th, not January the 7th, like Serbs and Russians do (Julian calendar is 13 days behind the Gregorian at the moment).
Even for the Romanian and Greek Orthodox churches, the Easter rarely coincides with the Catholic Easter. You are right about the Christmas though, it is on 25 for both churches.
All Orthodox Churches are still on the Julian Calendar, they've just adopted a version called the Revised Julian Calendar, which moves certain holidays so that they align with the West. The rest of the Calendar, apart from something like Christmas, is still Julian.
The calendar differences went on for a long long time. You should read "The Mysterious Numbers of the Hebrew Kings" to really grasp the types of issues that lead up to different calendars.
We are speaking of the church calendar. All Christian churches (there was no single "Eastern" church) as far as I know used the Julian calendar (named after and instituted during the reign of Julius Caesar) until Catholic church adopted Gregorian calendar.
| All Christian churches (there was no single "Eastern" church) as far as I know
There is the Eastern Orthodox Church (Russian Orthodox, Greek Orthodox, Bulgarian Orthodox, Georgian Orthodox, Ukrainian Orthodox, etc.) - This is all one Eastern church.
There is the Oriental Orthodox Church (Coptic Orthodox, Syriac Orthodox, Ethiopian Tewahedo Orthodox, Malankara Orthodox, etc.). This is all another Eastern Church.
There is also the Assyrian Church of the East, but ever since the war in Iraq and rise of ISIS, it's all but destroyed at this point.
Between those 3, those are the only "eastern" churches in existence apart from tiny schismatic groups. However, when someone refers to the Eastern Church, they are almost always referring to the first one, the Eastern Orthodox Church, since it's enormous and sat at the center of the Byzantine Empire.
I think there's a confusion between classification and hierarchy. I would always use the plural when referring to Eastern and even more so Oriental Orthodox Churches. They are independent entities, though they have affinities to each other and can be grouped together based on what ecumenical councils they recognize.
In contrast, there is single Catholic Church, and just a century prior to Gregory's time it united all Christians in the Western Europe, apart from a few heretical / protestant movements here and there.
They don't view themselves as separate, they view themselves as part of a unified whole. It seems very strange to pluralize them when they don't even pluralize themselves.
at the height of the Church’s calendar problem, in the second half of the 16th century, the eastern Church and the western Church were an incredible ten days out of sync with one another. This was only reconciled in 1582 when Pope Gregory XIII implemented what has become known as the Gregorian calendar reform.
This doesn't sound right at all. Why would the church calendars be out of sync at the time? In fact, it was the Gregorian reform that put them out of sync. They are still out of sync and the gap is growing.
Bonus history trivia question: What month did the Russian October Revolution happen?