By Dr Helen Parish, PhD, The University of Reading — The Conversation, 23 February 2022
The reason February is shorter than other months comes down to the history of how we measure and divide the year. In the first surviving ancient Roman calendar, there were only ten months, beginning in spring with March and ending 304 days later in December. In 731BC Numa Pompilius, the second king of Rome, decided to line the calendar up with the phases of the moon. January and February were added and the new calendar year lasted 355 days. The Romans believed that even numbers were unlucky, so the length of the months alternated between 29 or 31 days — leaving the final month, February, with only 28.
A 355-day calendar created problems because the Earth takes longer than this to orbit the Sun, causing the months and seasons to fall out of alignment over time. So an extra month called Mercedonius was added to the calendar before the start of March whenever needed to realign months and seasons — but it started on 24th February, cutting four days from an already short month.
Julius Caesar fixed this with the Julian Calendar in 45 BCE, creating a 365-day year with an extra day added to February once every four years — a leap year. However, an extra day every four years is slightly too much, causing the Julian calendar to drift by ten days by the 16th century. This led to the Gregorian Calendar introduced in 1582 by Pope Gregory XIII, which corrected this drift and remains in use today. Under the Gregorian calendar, no century year can be a leap year unless divisible by 400 — so 2000 was a leap year, but 1900 was not. This article has been republished under Creative Commons licence.