What are the missing 10 days of 1582?
Scroll back to October 1582 in the calendar on a smartphone or computer, and October 4 is followed by October 15; the ten days from the 5th to the 14th do not exist. These “lost ten days” were featured on the TV program Yarisugi Toshi Densetsu and became a topic like an urban legend. However, how it is displayed differs by device, app and settings.
The cause: the switch to the Gregorian calendar
This ten-day gap really happened in history. Until then, Europe used the Julian calendar established by Julius Caesar of ancient Rome. The Julian calendar counted a year as 365.25 days, but the actual (solar) year is about 365.2422 days, slightly too long. The difference built up over more than 1,000 years, and by the 16th century the calendar was about ten days out of step with the seasons.
To correct this, Pope Gregory XIII established the new Gregorian calendar and made the day after Thursday, October 4, 1582, Friday, October 15, skipping ten days at once. The days of the week continued without a break. At the same time, the leap year rule was changed to “skip three leap years every 400 years.”
A different “gap” in each country
The Gregorian calendar was first adopted by Catholic countries such as Italy and Spain, and other countries switched later. Britain and its colonies switched in 1752, so September 2 was followed by September 14, with eleven days lost. Japan decided to switch to the solar calendar in Meiji 5 (1872), making Meiji 5, December 3 into Meiji 6, January 1.
Why it is told like an urban legend
The surprise that a decision by a pope more than 400 years ago is still preserved in the smartphone we use every day may make it feel like a “hidden secret.” Mysteries of dates and calendars are also often brought up in talk of prophecies and the end of the world.
