What Is that In Kryptonian Years, Anyway?

Little known fact:

Long ago, in Julie Schwartz's "Answer Man" letter columns, we learned that Superman's birthday was on February 29th - meaning that Superman only had a birthday once every four years! Apparently, this is Superman's equivalent birthday according to the Earth calendar; Krypton's calendar was slightly different, with eighteen Kryptonian years for every twenty-five years on Earth. Presumably, Superman also has a Kryptonian date for his birth that he celebrates, just as Jewish children have a birthday in the Hebrew calendar. Make of that what you will.

Happy birthday, Kal-El!