Why does February have 28 days?
February (and January) first appeared on a calendar in about 713BC when Numa Pompilius (King of Roma from 715-673BC) added those two months to the existing 10-month long Roman calendar. He did so to ensure that the calendar accorded with the 12 lunar cycles (one lunar month is the time between two full moons – 30 days (rounded up)). A superstitious Roman, Numa wanted to avoid months being of even number. So, he subtracted a day from each of the ten 30-day months to make them each 29-days long. But, because he only had so many days to play with given that the calendar accords with the lunar cycle, at least 1 month of the year had to be constituted by an even number of days. He chose February. Because it was last to be added, it was also the last month of the year until about 450 BC when it was changed to the second month on the calendar.
The calendar was substantially reformed in 46 BC by Julius Caeser. Caeser’s reforms brought the calendar in line with rotation of the sun (as opposed to the moon) which meant that 1 year would add up to 365 days. In allocating the extra days, Caeser kept February with 28 days except for in the leap year which occurs every fourth year in a four-year cycle. The Julian calendar remained the predominant calendar used around the world for about 1,600 years. The Julian calendar is very familiar to the solar dating system most commonly used around the world now, the Georgian calendar. The Julian calendar operated on a cycle of 3 normal years (365 days) followed by 1 leap year (366 days) and is based on one solar year lasting for 365.25 days. However, this was an incorrect calculation. The correct solar year value is 365.24219 days (365 days, 5 hours, 48 minutes, 46 seconds). The error meant that on the Julian calendar, 1 extra day was gained every 128 years!
The Gregorian calendar was proclaimed by Pope Gregory XIII in 1582 to essentially overcome this error. Although, its adoption was not instant. Turkey was the last country to officially switch to the Gregorian calendar on 1 January 1927 (although it had changed for fiscal purposes in 1917)! Because the error the Georgian calendar was introduced to overcome was not so large as to accommodate another day being added into the calendar, February was stuck with only 28 days (but for leap years).