After 6 weeks of fun in the sun, the start of the new school term is now looming and many students will be wishing this week just would not come. It may sound like something slightly ridiculous to hope for, but in 1752 it is exactly what happened in Great Britain…

Okay – so this is not quite as mysterious as it sounds. Before September 2nd 1752, Britain, along with a large proportion of the western world, used a calendar known as the ‘Julian calendar’. Named after the infamous Roman emperor Julius Caesar, this calendar was, on a year by year basis, the same as the Gregorian calendar we use today but crucially varied in its use of leap years.

Mathematically, the reason for this change is simple to understand. The length of a year, defined by the time taken for the earth to perform a complete orbit of the sun, is 365.2422 days. In the Julian calendar, a day was added to February every four years, meaning each year was on average 365.25 days long. A difference of 0.0078 days a year seems insignificant: for example, in 35 years, the average life expectancy when it was first introduced in 45BC, the calendar would become just ¼ of a day ahead of the earth’s natural orbit. However, over the next 1500 years, as no changes were made to compensate for this small error, the calendar became over 10 days out of sync with the equinoxes.

Pope Gregory XIII thought to fix this error with the introduction of the Gregorian calendar, an identical calendar that was shifted to reconfigure with the Earth’s orbit but that also introduced new rules for leap years to delay a future error. It was officially introduced in England and the rest of the British Empire after September 2nd 1752, starting with September 14th 1752: so the intervening dates literally never happened.

In this new calendar, leap years occur every 4 years, excluding years divisible by 100 but including those divisible by 400. So, the year 2000 was a leap year but 2100 will not be. This changes the length of the average year to 365.2425 days, far closer to the actual value but again not quite accurate. If you’re waiting for a whole week to be completely missed out again, however, it will be approximately another 20000 years... so you might just have to go back to school.