Why does February have 28 days?
February is the second month in the Gregorian calendar. It only has 28 days.
While most months have either 30 or 31 days, February has only 28 days. In a leap year, that is, every fourth year, February has 29 days. February is the second month of the year in the Julian and Gregorian calendars. The Gregorian calendar is the most commonly used calendar today.
The Gregorian calendar is loosely based on the old lunar Roman calendar. Originally, there were only 10 months, from March to December, which were scheduled according to the seasons. The entire winter was considered as one month. Eventually, around 713 BC, Numa Pompilius added two more months, January and February at the end of the year, after December. This was done, so that the calendar would coincide with the 12 lunar cycles, i.e. the lunar calendar, which was 354 days long.
The new months each had 28 days, so as to total 354 days. However, every few years, February was truncated to 23 or 24 days, and a 27-day intercalary month, Intercalaris, was inserted into the year. This helped align the year back with the seasons, as the actual revolution of the Earth takes longer than 354 days, causing the year to misalign with the seasons. This eventually became a problem as Intercalaris was either often skipped entirely, or inserted wrongly.
Eventually, Julius Caesar came up with a solution. He banned Intercalaris all together, and realigned the year with the Egyptian solar calendar, which had 365.25 day. This was very close to the actual average length of a year, which is 365.2425 days. Under the Julian calendar, leap years occurred regularly every fourth year. This took into consideration the 0.25 days which were left over from a year. So, every fourth year an additional day was added to the month of February for a total of 29 days.
The Julian calendar also changed the order of the months, making January the first month of the year, February the second, and December the last. The Gregorian calendar continues all these changes, and added just one more to the system for determining which years were to be the leap years.