Today is the first day of the first of -ber months (Septem, Octo, Novem, and Decem). Happy day!
September derives from the Latin "septimus" or "seventh", and it used to be the seventh month of the Roman calendar... until the Roman calendar was changed in 153 BC, from the new year beginning in March to the new year beginning in January (and - not so surprisingly - the people didn't really want to change the names of the months).
So welcome to the so-called seventh month.
(Such realizations make it all the more obvious how culturally created measurements of time really is.)