Why February 29 is a leap day
It all started with Julius Caesar
What happened?
Don't call it a bonus day. But every leap year, we get a 29th day in February.
How we got here
Julius Caesar, "dealing with major seasonal drift" in Roman calendars, introduced the Julian calendar in 46 BCE, counting a year as 365.25 days and adding an extra day every four years, The Associated Press said. But a year is actually 365.242 days, so Pope Gregory XIII knocked out a leap year every hundred years — except years divisible by 400, like 2000. The 1582 Gregorian calendar "remains in use today" and, while its "gnarly math" is not perfect, it reduced "drift to mere seconds."
The commentary
"Without the leap years, after a few hundred years we will have summer in November" and Christmas in summer, said Younas Khan, a physics instructor at the University of Alabama at Birmingham. Some people treat Feb. 29 "as a free day" to do things "they've long been putting off," Phil Plait said at Scientific American. "I think that's a pretty good idea because, after all, catching up is what leap day is all about," astronomically speaking.
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What next?
There will be leap days every four years until the next skip year, 2100 — or till the Gregorian calendar is changed.
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