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## Leap babies

If you’re born on a leap day, do you have birthdays only once every four years?

View larger. | The small “block calendars” in the Astronomical Calendars for these two years, with blue color denoting moon-free nights.

Story by Guy Ottewell. Used with permission.

Leap day coming on Monday. The calendars above are a “common” year and a leap year side by side.

You can see that January 1 is a Thursday, then becomes in the next year a Friday; and this one-day jump is what ordinarily happens to all the dates in the year. But after the inserted February 29, all the dates take a two-day “leap”: March 1 leaps from Sunday to Tuesday, and so on. That is the presumed reason for this usage in English of the word “leap,” though it seems unproved. There are other terms for the added day: bissextile day (which takes some explaining), intercalary day.

The leap day is stuck into every 4th year (except century years not divisible by 4 – thus, 97 times in each 400 years). Why? To bring th average calendar year to 365.2425 days, closer to the solar year of 365.2422: the true seasonal year, measured by astronomy from one point in our journey around the sun to our next arrival at that point.

If you’re born on a leap day, do you have birthdays only once every four years? We can bet that such people claim to be only 15 when they’re 60, yet have it both ways by accepting birthday gifts and greetings arpund the ends of the leapless Februaries too. The number of leap-day babies is presumably about 97/(400*365.2425) = 0.0006663942 of the world’s population; something like 4 million. Or more, if conception is above average in May.

Not rare, anyway. Rarer is for the birth on a leap day to be twins; rarer again, triplets. Or for a mother to bear a baby on a leap day, and again on another leap day. Rarer again, on a third leap day. Rarer again, for those births to be twins; rarer again, triplets. I read somewhere that Mrs. Henriksen, Norwegian, bore triplets on 1960 February 29, 1964 February 29, and 1968 February 29. And Mrs. Louise Estes of Provo, Utah, achieved the same on the leap days of 2004, 2008, and 2012.

Self-portrait by Guy Ottewell

And beyond? What is all but impossible for physiology is easy for imagination. Quadruplets would be more appropriate, since February is the month of four weeks. Once upon a time, there was a queen who … And her children set out to find the four corners of the world. They had time to reach their goals, since they each lived to be 280.