ujm
“Why did we change our calculations for VTUM based on the Pope’s decision?”
We didn’t change, we use the exact same calculation. However the Calendar you use changed.
SO for example Lets say someoen decides that its too confusing to call December “December” since it isnt the 10’th month and for now on we will call December “Dodecamber” Naturally we will start Saying Vesein Tal umatar on Dodecamber 4 or 5th. But not becasue WE changed our nomenclature, but because they did
We count 60 days from Tekufas Shmuel We always have. and still do . Tekufas Shmuel Assumes the year to be exactly 365 days and 6 hours. The Julian Calendar assumes the same. Society follows the Gregorian Calendar. So we use a different date, not because we changed, but because they did.
Tekufas Shmuel on the Calendar we use fell out Oct 7 3 AM. count 60 days (Oct 7 is #1) and Day 60 will Be Shabbos Dec 5th. So at the satrt of Shabbos ie Friday night Dec 4th we would have started Vesein tal umatar if we said baruch aleinu on Shabbos
If you prefer to use the Julian Calendar and ignore Gregory’s change.
Then Tekufas Shmuel this year was Wed Sep 24 3 AM. (on the Julian Calendar) 60 days later is Shabbos Nov 22 on the Julian Calendar (that is this week PArshas Vayishlack Nov 22 Julian = Dec 5 Gregorian) and Vesein tal umatar is on the same day