Today is Bach's birthday for those of you who celebrate.
Like others of his day, Newton comes to mind, there is a bit of confusion over the real date given the day shift that occurred when the Julian Calendar was replaced by the current Gregorian calendar. The shift was messy taking place first in Roman Catholic countries in the late 1500s - after all, Spring must fall on roughly March 21 which was deemed useful for calculating Easter. But the shift to England and its colonies was delayed by about 150 years. Protestant Germany was somewhere in between and Bach's birthday is caught up in the mess.
Looking into the matter it turned out that all days prior to 1700 in Germany are considered valid. So by that decree today is the day. But if you count days you can wait until March 31.