Monday, February 28, 2011

February 29 birthdays

A friend of mine who drives a Chapel Hill bus told me this morning that a friend of hers was born on February 29, 1936.
    Naturally, we got to discussing the quandary of people born on February 29: If and when may they celebrate their birthdays in non-leap years? Will they celebrate today? Will they celebrate tomorrow? Will they not celebrate at all this year?
    If people born on February 29 may celebrate only the very day (each leap year), then my friend's friend may have celebrated eighteen birthdays (not counting the day of her birth).
    Is that all she's legitimately entitled to?
    By no means. Consider this:
    She was born the day after February 28. There have been 74 such days since February 29, 1936. My friend's friend may have celebrated 74 birthdays, and tomorrow she may celebrate her 75th.
    But wait a second. She was also born the day before March 1. Including today, there have been 75 such days since February 29, 1936.
    May she, then, celebrate her 75th birthday today—or, perhaps, her 75 + 74 - 18th (or 131st) birthday? (Subtract 18 so as not to double-count the February 29ths.) By this reckoning, people born on February 29 may celebrate two birthdays in non-leap years.
    My friend's friend may celebrate for her 132nd birthday tomorrow.
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Sequelae:
  1. March 2: When's your birthday time?
  2. March 3: Theological fallout from "birthtime"
  3. March 15: motomynd: "Quantity of life, or quality?"

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