Why February has 28 days? “Mathematically, to have 12 lunar months, you have to have one month that has an even number. So that was February,” Case said. The Romans dedicated the month to the God of purification and left it with an even 28 days. The ancestor of the Gregorian calendar was the first Roman calendar which had some differences: it consisted of 10 months rather than 12. In order to synchronise the calendar with the lunar year, the Roman king Numa Pompilius added 2 more months, January and February. The previous calendar had 6 months x 30 days and 4 months x 31 days = 304 days. Numa wanted to avoid having even numbers in the calendar, as the Romans were superstitious and even numbers were unlucky. He subtracted a day from each of the 30-day months to make them 29 and since the lunar year has 355 days (or 354.367 to be exact) which meant that he had 57 days left to share into 2 months. Hence, he gave January 29 days like the other months and February 28 days since at least one month out of 12 needed to contain an even number of days. The sum of any even amount (12 months) of odd numbers will always equal an even number and he wanted the total to be odd. So Numa chose February to be the unlucky month of 28 days since that month hosted the Roman rituals to honour the dead. Despite other changes in them modern calendar, Numa’s shortening of February stayed with us! n Indiana, February brings on long and cold days. After surviving the cold temperatures and inclement weather of December and January, Hoosiers impatiently wait for March to welcome spring. And each year, the small amount of hope we have is that February won’t last too long. After all, it is two to three days shorter than every other month. This got us thinking, why does February only have 28—and sometimes 29—days, anyway? Today, we answer that question with help from Slate and Mental Floss Magazine. Early Roman calendars February’s 28 days date back to the second king of Rome, Numa Pompilius. Before he became king, Rome’s lunar calendar was just 10 months long. It began in March and ended in December. At the time, Romulus—the first king of Rome—and his people found the time between December and March to be unimportant because it had nothing to do with the harvest. When Numa Pompilius took reign, he decided to make the calendar more accurate by lining it up with the year’s 12 lunar cycles. The new 355-day year needed two additional months to make up for the lost time. So he added January and February to the end of the calendar. Because Romans believed even numbers to be unlucky, each month had an odd number of days, which alternated between 29 and 31. But, in order to reach 355 days, one month had to be an even number. February was chosen to be the unlucky month with 28 days. According to Slate, this choice may be due to the fact that Romans honored the dead and performed rites of purification in February. In fact, the word februare means “to purify” in the dialect of the ancient Sabine tribe. After a few years of using the Numa Pompilius’ new 355-day calendar, the seasons and months began to fall out of sync. In an attempt to realign the two, the Romans added a 27-day leap month called Mercedonius. If Mercedonius was used, it began on February 24. Julian calendar Because the leap month was inconsistent, this too had its obvious flaws. In 45 BCE, Julius Caesar commissioned an expert to create a sun-based calendar like the one the Egyptians used. The Julian calendar added a little more than 10 days to each year, making each month either 30 or 31 days long, except for February. To account for the entire 365.25 day-long year, one day was added to February every four years, now known as a “leap year.” During most years, this left February with just 28 days.