Western experts explain the history and science behind leap years

Two experts explain why we have leap years and the significance behind the calendar anomalies

 February 28, 2024

 February 28, 2024

Every four years the world experiences an unusual but necessary event, an extra day known as a leap year. But did you know there was a point in time when 90 leap days were necessary?  

Two Western University experts are available to media to explain the history and science behind leap years and why we still require them to this day.   

According to classical studies professor Alexander Meyer, leap years can be traced back to the infamous Roman Emperor, Julius Caesar.  

“The previous Roman calendar needed constant correction and could be, and was, manipulated for political reasons,” said Meyer, who studies Roman imperial history along with ancient clocks and calendars and researches identity in antiquity and Roman provincial studies. 

“The problems had gotten so bad by 46 BCE that Caesar had to add 90 days to the year to bring it back into alignment with the solar year and the seasons.” 

As part of his calendar reform Caesar introduced a leap day, which was to be inserted in the calendar every fourth year after February 24. However, according to Meyer, Caesar was assassinated before he could see the plan implemented properly. 

It wasn’t until 1582 when Pope Gregory XIII put into place the modern Gregorian calendar and leap year system. 

However, the question remains: Why are human calendars so imperfect as to require an extra day every four years? 

Physics and astronomy professor Pauline Barmby has the answer. 

“We need leap years because the year (the time it takes the Earth to go around the Sun) is not a perfect number of days,” said Barmby, who is chair of the department of physics and astronomy and specializes in observational studies of star formation and stellar populations in nearby galaxies.  

“If we ignored this, the calendar would get out of sync with the seasons. The year is close to 365.25 days, so adding an extra day every four years gets close to fixing this.” 

Despite adding these extra days, it doesn’t perfectly correct for the discrepancy due to another astrological situation: the Earth’s rotation is gradually slowing.   

Over the past few millennia the Earth’s rotation has slowed meaning our days are getting slightly longer. Though the change is relatively minor it does add up over time, which also impacts our calendars.  

“The International Bureau of Weights and Measures, located in Sèvres, France, oversees precise timekeeping and addresses the slowing rotation by adding ‘leap seconds’ every couple of years,” said Barmby.  

“There is a plan to stop doing this in 2035, meaning eventually some other way to keep everything in sync will need to be created.” 

MEDIA CONTACT: Justin Zadorsky, Media Relations Officer, Western University, 226.377.1673 (mobile), 



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