Science

Leap Year 2016: Why Feb. 29 Happens Only Every 4 Years

At the end of the month, Feb. 29 will return from its four-year vacation to make this year a leap year.

But why does that happen?

Simply put, it’s because Earth doesn’t revolve around the sun in exactly 365 days.

The term "leap year" is a misnomer. It means there’s an extra day on the calendar, making the year 366 days long instead of 365 like a common year.

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Astronomers set a year as the time it takes from one spring equinox to the next.

While that does take 365 days to do so, there’s some excess time that’s commonly disregarded.

It takes the Earth roughly 365.242199 days, or 365 days, 5 hours, 48 minutes and 46 seconds to make its trip around the sun.

That excess 5 hours, 48 minutes and 46 seconds is where we get our 366th day during a leap year, Feb. 29. The extra day is added into February because it was last month in the Roman calendar and allowed for correction before the new year began.

Without adding that extra day every four years, our calendars would become out of sync.

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In other words, the calendar would lose just about a day every four years if not accounted for in the leap year. That means that 25 days would be lost every century, which would eventually shift months into different times of the year, which could make July a winter month in the Northern Hemisphere, says EarthSky.

The name “leap year” comes from “leap day” and affects how days of the year line up with days of the week.

For example, in 2013, July 23 fell on a Tuesday. In 2014, it fell on a Wednesday, and then Thursday in 2015. However, in 2016 it will fall on a Saturday, leaping Friday due to the extra day in February.

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