Yep....

"AD" stands for Anno Domini, Latin for "In the Year of Our Lord."  Calendars and the way we keep track of time, for convenience and by convention, are interesting studies.

There are more than 40 calendars extant in the world today.  Fewer than a dozen, however, are widely used.

Calendars are both solar and lunar.  The Chinese, centuries ago, tried to mesh their lunar calendar with a solar one, with middling success.  The Islamic calendar is a lunar one.  Most others are solar.

When the Gregorian calendar was made and enacted in 1582 AD (!), it added ten days to the then used Julian calendar.  There were rumblings, if not riots, among many commoners because they thought they'd be losing ten days of their lives as the calendar moved forward.  Britain, of course then a Protestant nation thanks to Henry VIII, didn't convert to the Catholic Gregorian calendar.  It finally did change in 1751 (or maybe year later; I always mix up the date with Ben Franklin's first academic paper on electricity), then adding eleven days.  Geo Wash was actually born on Feb 11, but his "birthday" became Feb 22; likewise Franklin, from Jan 6 to the 17.  No worry, in our infinite wisdom, we moved Wash's birthday, averaging it with Lincoln's (originally Feb 12), to have a President's Day.  (If that is to "honor" all Presidents, does that include A. Johnson, W. Wilson, among others???)

Hmmm....  Was the Bolshevik Rev Oct 25-26 or Nov 6-7?  It depends on the calendar consulted.  The Russians were still using the Julian calendar, the so-called "Old Style" one.  In the West, of course, the "New Style" calendar was in use.

BTW, when Julius Caesar added about 90 days to the year (45 BC), he was trying to match up the traditional months with the traditional seasons.  Romans were flustered and referred to 45 BC as "the year of confusion."  Hey, I'm confused right now!