The day that ran longer than it should

In October 1582, in several countries of Europe, whoever went to bed on Thursday the 4th woke up on Friday the 15th. Ten days were wiped from the calendar in a single jump.

It was not a mistake but a correction. The old Julian calendar reckoned the year slightly longer than it really is, and over the centuries that small drift had built up ten days of lag behind the rhythm of the seasons. Pope Gregory XIII pushed through a new calendar, the Gregorian one we use today, and to bring the dates back into line those days had to be dropped.

Not every country adopted it at once. Some took centuries, so for a long time two places could live the same instant under different dates on paper.

Source: Royal Museums Greenwich