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Feb. 29 is a date that happens only once every four years , but what are leap geezerhood ? Why do we need them ? And how did they amount about ?
Leap twelvemonth are year with 366 calendar days instead of the normal 365 . They take place every quaternary year in theGregorian calendar — the calendar used by the legal age of the world . The extra mean solar day , screw as aleap daylight , is Feb. 29 , which does not exist in non - leap year . Every class that is divisible by four , such as 2020 and 2024 , is a leap year except for some centennial years , or years that end in 00 , such as 1900 . ( We ’ll explain why further down . )
The next leap year will be in 2028
The name " leap " comes from the fact that from March onward , each escort of a leap yr moves forward by an extra day from the previous class . For case , March 1 , 2027 will be a Monday but in the next leap yr , 2028 , it will come on a Wednesday . ( Normally , the same appointment only move forth by a exclusive day between consecutive year . )
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Other calendars , including the Hebrew calendar , Islamic calendar , Chinese calendar and Ethiopian calendar , also have versions of leap years , but these twelvemonth do n’t all follow every four years and often occur in different old age than those in the Gregorian calendar . Some calendar also have multiple leap days or even shortened leap months .
It takes roughly 365.24 days for Earth to orbit the sun, which is slightly longer than a standard calendar year.
In addition to leap years and leap 24-hour interval , the Gregorian calendar also has a fistful of leap seconds , which have periodically been added to certain eld — most recently in 2012 , 2015 and 2016 . However , the International Bureau of Weights and Measures ( IBWM ) , the organization responsible for global timekeeping , willabolish leap minute from 2035 onward .
Why do we need leap years?
On the face of it , all of this " leap " may seem like a silly idea . But leap years are very crucial , and without them our years would finally depend very dissimilar .
Leap year exist because a single year in the Gregorian calendar is slenderly shorter than a solar , or tropical , twelvemonth — the amount of fourth dimension it takes for Earth to totally orbit the sun once . A calendar year is just 365 days long , but a solar yr is roughly 365.24 days long , or 365 days , 5 hours , 48 minutes and 56 seconds .
If we did not calculate for this departure , then for each yr that pass the col between the starting line of a calendar year and a solar year would extend by 5 minute , 48 minutes and 56 seconds . Over time , this would pitch the timing of the season . For exemplar , if we check using leap years , then in around 700 years the Northern Hemisphere ’s summertime would start in December instead of June , according to theNational Air and Space Museum .
This year we will get an extra day, or leap day, on Feb. 29.
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Adding leaping day every quaternary twelvemonth largely removes this problem because an extra day is around the same length as the difference that accumulates during this time .
However , the scheme is not utter : We gain around 44 superfluous minutes every four twelvemonth , or a day every 129 years . To lick this job , we jump the leap age every centenary year except for those that are divisible by 400 , such as 1600 and 2000 . But even then , there is still a flyspeck difference between calendar years and solar years , which is why the IBWM have experimented with leap second .
The Julian calendar was introduced by Julius Caesar in 46 B.C.
But overall , leap years think that the Gregorian calendar stays in sync with our journey around the sun .
When was the last leap year? When is the next leap year?
The history of leap years
The idea of leap twelvemonth dates back to 45 B.C. when theAncient RomanemperorJulius Caesarinstituted the Julian calendar , which was made up of 365 day disunite into the 12 month we still use in the Gregorian calendar . ( July and August were earlier named Quintilis and Sextilis respectively but were later rename after Julius Caesar and his successor Augustus . )
The Julian calendar included leap years every four years without exclusion and was synced up to Earth ’s season thanks to the " final year of confusion " in 46 B.C. , which included 15 calendar month add 445 day , according to theUniversity of Houston .
For C , it appear that the Julian calendar work perfectly . But by the mid-16th century , astronomers noticed that the season were beginning around 10 day in the beginning than expected when important holidays , such as Easter , no longer match up with specific events , such as the vernal , or spring , equinoctial point .
To rectify this , Pope Gregory XIII introduce the Gregorian calendar in 1582 , which is the same as the Julian calendar but with the riddance of leap years for most centenary years ( as sketch above ) .
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For centuries , the Gregorian calendar was only used by Catholic country , such as Italy and Spain , but it was eventually adopted by Protestant body politic , such as Great Britain in 1752 , when their years began to greatly deviate from Catholic rural area .
Because of the disagreement between calendars , nation that later switched to the Gregorian calendar had to hop day to sync up with the respite of the public . For case , when Britain swapped calendar in 1752 , Sept. 2 was followed by Sept. 14 , concord to theRoyal Museums Greenwich .
At some point in the remote future , the Gregorian calendar may have to be re - evaluated as it slip out of sync with solar age . But it will take thousands of years for this to happen .
Why is leap day on Feb. 29?
In the 8th century B.C. , the Roman calendar had just 10 months , beginning in March and terminate in December . The insensate winter season was ignored , with no month to mean it . But this calendar had only 304 day , so January and February were finally added to theend of the religious class . As the last month , Februaryhad the fewest days . But Romans soon began associate these months with the start of the civic class , and by around 450 B.C. , January was reckon as the first month of the novel twelvemonth .
When Pope Gregory XIII added the leap day to the Gregorian calendar in 1582 , he chose February because it was the shortest calendar month , making it one sidereal day longer on leap old age .
