Why we need Leap Years

Leap Day!

On Saturday, we’ll be celebrating Leap Day, which comes around every four years and offers us one extra day to eat pizza.

So what’s the deal with Leap Days and Leap Years? Why’re we leaping? Can’t we just... not leap?

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(This first appeared in the Morning Report Newsletter! Sign up for it here)

Why we leap

According to EarthSky.org, Leap Days help synchronize our human-created calendars with Earth’s orbit around the sun and the actual passing of the seasons.

“Why do we need them? Blame Earth’s orbit around the sun, which takes approximately 365.25 days. It’s that .25 that creates the need for a leap year every four years.”

So, during non-leap years, the calendar doesn’t account for the extra quarter of a day that would be required by Earth to complete a single orbit around the sun. As usual, this is a human problem. We’re so problematic, aren’t we?!

Leap history

Here’s some history from NASA:

In 46 BC, Julius Caesar, created a calendar system that added one leap day every four years. Acting on advice by Alexandrian astronomer Sosigenes, Caesar did this to make up for the fact that the Earth’s year is slightly more than 365 days.

In modern terms, the time it takes for the Earth to circle the Sun is slightly more than the time it takes for the Earth to rotate 365 times (with respect to the Sun -- actually we now know this takes about 365.24219 rotations).

So, if calendar years contained 365 days they would drift from the actual year by about 1 day every 4 years. Eventually July (named posthumously for Julius Caesar himself) would occur during the northern hemisphere winter!

By adopting a leap year with an extra day every four years, the calendar year would drift much less. This Julian Calendar system was used until the year 1582 when Pope Gregory XIII added that leap days should not occur in years ending in “00” except if divisible by 400, providing further fine-tuning.

This Gregorian Calendar system is the one in common use today. Therefore, even though this year 2000 ends in “00”, it remains a leap year, and today is the added leap day. That makes today the first leap day for a centurial year since year 1600 and the second such leap day of the Gregorian Calendar.

Related: 7 of our favorite Leap Day 2020 freebies, deals


About the Author:

Ken Haddad has proudly been with WDIV/ClickOnDetroit since 2013. He also authors the Morning Report Newsletter and various other newsletters, and helps lead the WDIV Insider team. He's a big sports fan and is constantly sipping Lions Kool-Aid.