Long ago when the Romans developed the 12 month calendar the names we call, September, October, November, and December were based on their words for the numbers seven, eight, nine, and ten. The first month of their year was May, a name we've derived from Maia, their goddess of Spring. It was logical to start the new year when new life appeared.
The months alternated between 31 and 30 days. The Romans didn't plan for leap years.
The emperor, Julius Caesar, had the first Summer month of July named for himself. Then when Caesar Augustus became the next emperor he wanted a summer month named after him, but he didn't want it to be shorter than July because it might seem less important. That's why he took one day from the last month of the year, February, and added it to his own month of August.
Can you guess those men were both just a bit conceited?
If you want to remember the number of days in a certain month you don't need to remember the old rhyme, "30 days hath September, April, June and November," although that works well. Instead just remind yourself that the months alternate between 30 and 31 days, except for August and February.