Protestant tract writers responded to Gregory’s calendar by calling him the "Roman Antichrist" and claiming that its real purpose was to keep true Christians from worshiping on the correct days.
The "new" calendar, as we know it today, was not adopted uniformly across Europe until well into the 18th century.
But, hundreds of years later, monks were the only ones with any free time for scholarly pursuits and they were discouraged from thinking about the matter of "secular time" for any reason beyond figuring out when to observe Easter.
In the Middle Ages, the study of the measure of time was first viewed as prying too deeply into God’s own affairs and later thought of as a lowly, mechanical study, unworthy of serious contemplation.
Come to think of it, while they’ve showed up on your Instagram feed and you tag them on Twitter, they’re yet to share any indication that you’re hanging out together.
Before today’s Gregorian calendar was adopted, the older Julian calendar was used.
It was admirably close to the actual length of the year, as it turns out, but the Julian calendar was not so perfect that it didn’t slowly shift off track over the following centuries.
By the time he reformed the Julian calendar in 1582 (using the observations of Christopher Clavius and Johannes Kepler), it had drifted 10 days off course.
To this day, most of the world uses his Gregorian calendar.