Trying to be smart once — once, mind you — I wished someone “happy ides of June” on the 15th of the month. I happened to say it to one of the few people I’ve ever met who could instantly set me straight. My assumption was that since the ides of March is the 15th, then it follows that the 15th of every month would be the ides. But my friend and sometimes trivia nemesis — I’ll call him Randy, since that’s his name –said, “Oh, it’s not the ides of June.”
That’s because we’re dealing with an artifact of the ancient lunar version of the Roman calendar — which has a series of special days to account for (kalends, nones, and ides), The long story short: the ides (which originally was supposed to designate the full moon) falls on the 15th in four months: March, May, July, and October. The rest of the time it falls on the 13th.
Inquiring minds want to know.