Raleigh News & Observer Logo

Why do we have leap year? | Raleigh News & Observer

×
  • E-edition
    • Customer Service
    • Support
    • Contact Us
    • About Us
    • FAQ
    • Sponsorships
    • Stay connected
    • Mobile & Apps
    • Facebook
    • Google+
    • Instagram
    • Twitter
    • Social Media Directory
    • N&O Store
    • Buy Photos
    • Databases
    • Archives
    • Newsletters

    • Blogs
    • Columnists
    • Crime
    • Education
    • Health
    • Local
    • North Carolina
    • Nation/World
    • Science
    • Thumbs Up
    • Traffic
    • Weather
    • Weird News
    • All News
    • Counties
    • Durham County
    • Johnston County
    • Orange County
    • Wake County
    • All Sports
    • Baseball
    • Canes
    • College
    • Columns & Blogs
    • High Schools
    • NASCAR & Auto Racing
    • NBA
    • NFL
    • NHL
    • Olympics
    • Outdoors
    • Panthers
    • Soccer
    • Schools
    • Duke
    • East Carolina
    • NC State
    • North Carolina
    • All Politics
    • The North Carolina Influencer Series
    • State Politics
    • Blogs
    • Columnists
    • PolitiFact
    • PolitiFact NC
    • Rob Christensen
    • Under the Dome
    • All Business
    • Blogs
    • Columnists
    • Health Care
    • Personal Finance
    • Real Estate
    • Shop Talk
    • Stocks Center
    • Technology
    • All Living
    • Video Now
    • Best-Kept Secrets
    • Blogs
    • Celebrations
    • Comics
    • Family
    • Fashion
    • Fitness
    • Food
    • Games and Puzzles
    • Home and Garden
    • Horoscopes
    • Mouthful
    • Past Times
    • Pets
    • Religion
    • Travel
    • Video Now
    • Arts News
    • ArtsNow
    • Books
    • Contests
    • Dining
    • Entertainment
    • Games
    • Movies
    • Music
    • Nightlife
    • Television
    • On the Beat
    • Happiness is a Warm TV
    • All Opinion
    • Columnists
    • Dwane Powell
    • Editorials
    • Influencers Opinion
    • Letters
    • Opinion Shop Blog
    • Other Views
    • Submit a Letter
  • Obituaries

    • Advertise with us
    • Place Ad
    • Apartments
    • Cars
    • Homes
    • Jobs
    • Legals
    • Obits/In Memoriams
    • Weddings
    • Today's Daily Deal
    • Special Sections
    • Today's Circulars
    • Rewards
    • Photo Store
  • Classifieds
  • Jobs
  • Moonlighting
  • Cars
  • Homes
  • Legals

SciTech

Why do we have leap year?

BY MARLA VACEK BROADFOOT - Correspondent

    ORDER REPRINT →

February 27, 2012 02:00 AM

Robert Egler, senior lecturer in physics and director of instructional labs at N.C. State, explains why we have that extra day this month. Questions and answers have been edited.

Q: Why is a leap year necessary?

The actual time it takes the Earth to complete one orbit of the sun - called a "tropical year" - is 365.2422 days. Thus a standard calendar year of 365 days is 0.2422 days, or 5 hours, 48 minutes, 46 seconds short of the actual year. If this isn't corrected, the calendar year will lose one day in relation to the actual year about every 4.4 years. At this rate, the start of the calendar year will be about 24 days early in 100 years. Since this is approximately one day in four years, every four years (with exceptions) we add one extra day to the calendar year to bring it back in line with the actual year.

A leap year every four years is equal to an average length of the calendar year of 365.2500 days, known as the "Julian year." Better than 365 days, but still not the same as the actual year of 365.2422 days. An average year of 365.2500 days still is wrong by 11 minutes and 14 seconds each year. This doesn't seem like much, but over time it adds up: 1 day in 128 years. If we make a slight change by saying that century years - 1700, 1800, 1900, 2000, etc. - are not leap years, unless they are evenly divisible by 400, we get an average year of 365.2425 days, which is only wrong by 26 seconds a year.

Sign Up and Save

Get six months of free digital access to The News & Observer

SUBSCRIBE WITH GOOGLE

#ReadLocal

Q: Who invented leap year?

The leap year was invented by the Romans in 46 BC, credited officially to Julius Caesar, but actually derived by the astronomer Sosigenes at the request of Caesar. By 46 BC, the date of the spring equinox had slowly shifted about 81 days out of place in the Roman calendar, so Caesar added 81 days to reset the year to the correct date, and introduced the leap year to help it stay in the right place. The Roman leap year was every four years without exception. This version, called the Julian calendar in honor of Julius Caesar, has the average year as 365.2500 days.

By AD 1582 the error between the calendar year of 365.2500 days and the actual year of 365.2422 days had once again accumulated to about 10 days, which was messing up the date of Easter. So in February 1582, Pope Gregory XIII issued an order, known as the Inter Gravissimas, that reset the start of the year by dropping 10 days out of the calendar that year. The Gregorian calendar is the calendar we follow today.

Q: How far off would our seasons be if leap years were never invented?

If Caesar had never reset the calendar and instituted the leap year, the accumulated error today would be about 580 days. In other words, we would have lost one entire year and an additional 214 days, and today mid-winter would actually be in June. January would be the height of summer vacation season.

  Comments  

Videos

Meet Moros: A newly discovered tiny Tyrannosaur

Become cyber savvy...protect against phishing attacks

View More Video

Trending Stories

Three observations from No. 8 North Carolina’s 88-72 road win over No. 1 Duke

February 21, 2019 02:18 AM

Zion Williamson injured as No. 1 Duke falls to No. 8 UNC

February 20, 2019 11:11 PM

Zion Williamson injured during Duke-UNC game after foot blows through shoe

February 20, 2019 09:53 PM

Will Zion Williamson play again for Duke? He’s listed as ‘day-to-day.’

February 21, 2019 04:43 PM

What in the world happened to Zion Williamson’s shoe? A sneaker expert weighs in.

February 21, 2019 05:15 PM

Read Next

Business

BMW, Daimler launch car- and ride-sharing joint venture

The Associated Press

    ORDER REPRINT →

February 22, 2019 05:16 AM

Automakers Daimler and BMW are formally launching their joint venture in services that make it possible to use their cars without necessarily owning one.

KEEP READING

Sign Up and Save

#ReadLocal

Get six months of free digital access to The News & Observer

SUBSCRIBE WITH GOOGLE

MORE SCITECH

Ashland clears way for Uber, Lyft to launch services

Business

Ashland clears way for Uber, Lyft to launch services

February 22, 2019 01:24 AM
Chicago’s vast camera network helped solve Smollett case

Celebrities

Chicago’s vast camera network helped solve Smollett case

February 22, 2019 01:08 AM
Cellphone internet access bringing changes fast to Cuba

Business

Cellphone internet access bringing changes fast to Cuba

February 22, 2019 12:29 AM
Claims in El Chapo case highlight perils of ‘Googling juror’

Business

Claims in El Chapo case highlight perils of ‘Googling juror’

February 21, 2019 09:30 PM
White House ends California talks on mileage dispute

Business

White House ends California talks on mileage dispute

February 21, 2019 08:27 PM
Nestle, AT&T pull YouTube ads over pedophile concerns

Business

Nestle, AT&T pull YouTube ads over pedophile concerns

February 21, 2019 07:49 PM
Take Us With You

Real-time updates and all local stories you want right in the palm of your hand.

Icon for mobile apps

Raleigh News & Observer App

View Newsletters

Subscriptions
  • Start a Subscription
  • Customer Service
  • eEdition
  • Vacation Hold
  • Pay Your Bill
  • Rewards
Learn More
  • About Us
  • Contact Us
  • Newsletters
  • News in Education
  • Triangletoday.com
  • Legal Notices
Advertising
  • Advertise With Us
  • About Our Ads
  • Place a Classified
  • Local Deals
  • N&O Store
  • N&O Photos
Copyright
Commenting Policy
Report News
Privacy Policy
Terms of Use


Back to Story