The year 2015 will be longer than 2014 by one second, scientists say, with the time added to keep atomic clocks in sync with the rotation of the earth -- which is slowing down.

Just before midnight of June 30, clocks running on atomic time will mark an additional "leap second" before switching over to the next day.

While atomic clocks, which measure time using the vibrations of atoms, are constant, the Earth's rotation is not, so the "leap second" has to be added every few years to allow the slowing earth and our atomic timekeepers to remain in sync.

The rotation of the Earth is slowing by about two-thousandths of a second a day.

While seeming insignificant, the extra added leap second can cause problems for the infrastructure of the Internet, as increasing numbers of computers and servers are synced to atomic clocks.

Many use the Network Time Protocol, or NTP, to keep themselves in sync, but most are not programmed to handle an unexpected additional second.

When the atomic clocks show them the same second -- 11:59:59 -- twice in a row, problems can ensue.

Programs meant to execute at a particular moment can become confused, and emails received at the exact "leap second" instance can get misdirected.

In 2012, when the last leap second was added, Google used a special update it called a "leap smear," adding a tiny bit of time with each update of their servers so when the leap second occurred, they were already in sync.

Not everyone is a fan of the leap second, which has been added 25 times since they were first used in 1972, or even considers it necessary.

A number of countries, including the United States, urge the ending of the leap second, proposing that atomic clocks be allowed to keep their constant time even if that means they gradually run away from the Earth's rotational time.

Not everyone thinks that would be a good idea.

Britain, in particular, argues the leap second should be maintained, since phasing it out would bring the end of Greenwich Mean Time, which is based on the sun and Earth's rotation and would gradually become increasingly inaccurate with the leap second adjustments.

Scientists and officials at the International Earth Rotation Service based in France are responsible for monitoring the planet's rotation and adding the leap second when necessary.

Since the Earth's rotation tends to "wobble" a bit, some years the planet runs right on time and no adjustment is necessary.

However, the Paris Observatory has announced one will be used this summer.

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