We're having a leap second this year at New Year's. The atomic clocks will briefly read "11:59:60 pm" (after reading "11:59:59 pm") Dec 31, before finally rolling over to 12:00:00 am, January 1.
One of my close high school friends says her birthday is the Ides of March (March 15), but it's really the 15th day of the 3rd month in the Chinese calendar. She was born in China, in the third month of their calendar, on the 15th day of that calendar, so when they emigrated they put down our third month (March) and 15th day (March 15, the Ides of March, per Julius Caesar fame). However, the luni-solar calendar doesn't start on our January 1, it starts (IIRC) two New Moons after Winter Solstice - which is usually early February or occasionally late January. So the date she was born according to the Western solar calendar (what we use in the USA) was "actually" sometime around early April through mid May. What date her Chinese birthday falls on will then vary every year, since our calendars are not in sync. Hence the simplicity of just saying it's the Ides of March every year.
And if you got that explanation of mine, try out this explanation of when Sir Isaac Newton's birthday should be.