Why February has only 28 days?
There was a lot of unknowing messing around with the calendar in the past.
The western calendar is a solar calendar which has 365 days. In the ancient times a lunar calendar made more sense since looking up at night told you the time of the month, which was important in agriculture. In the absence of printed calendars and other modern knowledge, the timing of the seasons for planting and harvesting was gauged by watching the moon. The lunar calendar has 355 days. It was of course an irritating few days off of the solar year which the seasons followed. This led to a lot of changes to the calendar.
The Roman calendar used to have 10 months. King Numa Pompilius increased the number to 12 months by adding January and February at the end of the year. To make the days work out February was shorter. The reshuffling of the months was done by Emperor Julius Caesar. There were further changes to the calendar were made as time past. February remained short to make the days work out.
For more than you ever wanted to know about the Roman calendar try:
For something crazy try the calendar of the French revolutionaries: