Misconstrued time

Within "Who Decides What Year It Is Anyhow?" comes a clear explanation of a one-time important change in the calendar:

Our current calendar, with its recognizable 12 months — one of them shorter than the rest — and a leap year every four years, takes its form from the Julian Calendar. Proposed by the famed Julius Caesar....

In the 16^th century, Pope Gregory XIII issued a decree that addressed a seemingly small problem with the Julian Calendar. The Julian Calendar assumed that the sun’s circuit is exactly 365.25 days (thus providing a leap year every four years). In actuality, the sun takes 365.2422 days to complete its path. While this differential — only 11 minutes or so — may seem too trivial to matter, those 11 minutes morphed the calendar after several centuries. The dates were straying farther away from the solar markers of time, such as the Spring Equinox and Summer Solstice. When Renaissance scholars took notice of this issue, they learned that the Julian Calendar was over-correcting by approximately eight days each millennium. ....

.... In the year 1582, Catholic Christendom hopped from October 4 to October 15 overnight to correct the languishing problem of misconstrued time. If you thought the calendar couldn’t get more confusing, you’re wrong! To make matters worse, many nations around the globe did not adopt the Gregorian Calendar until centuries after 1582. For hundreds of years, nations were operating ten calendar days apart. (Pity the historians who have to track such discrepancies.) Netherlands, Denmark, and Sweden did not transition to the Gregorian calendar until 1700. Great Britain and the United States followed suit in 1752, and Eastern countries including China, Turkey, and Russia did not switch until the early 20^th-century.

For those of us concerned about a seventh-day Sabbath—Jews and some Christians—it should be noted that although dates were affected by the change from the Julian to the Gregorian calendar, the weekly cycle was unaffected. If in 1582 Oct. 4 was a Thursday, the next day, Oct. 15, was still a Friday.

Kayla Bartsch, "Who Decides What Year It Is Anyhow?," National Review, December 31, 2023.