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Dr. Larry Lurio
Professor and Chair of Northern Illinois University’s Department of Physics

Northern Illinois University

What is a leap year?
In a leap year there are 366 days instead of the usual 365 days.  They occur on years divisible by 4, (like 2016). We have leap years because a year is actually 365.24 days.  By adding in a day every four years we keep the calendar in sync with the seasons. We even have to skip leap years occasionally to make things work out just right.

Why is it called leap year?
The name “leap year” dates from a note in a seventeenth century prayer book about how to deal with the mess that you get when you start throwing extra days into the calendar. You have to “leap” over the schedule to keep things in sync.

What would happen if we didn’t have one?
For a while, most people wouldn’t notice.  Gradually the calendar would start getting out of sync with the seasons.  For example, right now New Year’s Day is in the middle of winter.  After about 800 years, if we kept skipping leap year, News Year’s day would be in the middle of the summer.  (Although I suppose it already is, if you live in Australia)

What happens if your birthday is Feb 29?
If your birthday falls on the 29th it is typically celebrated on the 28th, and legally as well.  Of course, some people count their age as only ¼ of their true age, which was the plot for Gilbert and Sullivan’s Pirates of Penzance.  Legally, though, your birthday is the day before (that is, February 28th).  There was even a murder case once in Illinois where the defendants status as a Juvenile may have depended on how his birthday was counted (as he was born on the 29th).