You ever get the feeling that the day is just longer than ever? You've completed every task at work, but the clock has barely moved. While that phenomenon's usually a cruel trick, Tuesday will actually be longer. Leap second is a very real thing, and it will add a whole second to your day. What will you do with all that extra time?

Leap second is caused by the difference between two rather trustworthy ways of determining the length of a day. The first way is a simple one measuring the mean solar day -- its average length based on the Earth's rotation -- which is roughly 86,400.002 seconds long, according to NASA. The second way of figuring the length of a day is through Coordinated Universal Time (UTC), which is based on the "electromagnetic transitions in atoms of cesium": The atomic clock is incredibly accurate and won't need to be rewound for about 1.4 million years.

While both ways of measuring the length of a day are generally synchronize, it's that 0.002 of a second that causes the problem in need of a solution and leading the addition of a leap second. The Earth's rotation is slowing down -- there are a lot reasons for it, ranging from seasonal weather changes to ice storage to oceanic tides and even to El Nino -- as indicated by the Very Long Baseline Interferometry (VLBI) technique employed to measure our planet's rotation. VLBI uses quasars, astronomical objects in active galaxies, and measures how long it takes for each station in a network around the Earth to receive signals.

There's no fixed number of years between the additions of leap seconds -- the last leap second arrived in 2012, while the one before that came in 2008. Before 2005, the last leap second was added in 1998, preceded by another clock adjustment in 1997. A leap second typically has been added on either June 30 or Dec. 31 to ensure the figures calculated by employing the mean solar day and the UTC do not grow too far apart.

In this case, NASA said: "Normally, the clock would move from 23:59:59 to 00:00:00 the next day. But with the leap second on June 30, UTC will move from 23:59:59 to 23:59:60, and then to 00:00:00 on July 1." Most of us will be sleeping through the leap second, but the change could affect websites and technology companies using Java or Linux. Other systems will adjust for the additional second by turning off and turning back on to get back on time.

Meanwhile, there's plenty of debate over the way we keep track of days, with some suggesting we ditch the Earth's rotation a means of telling time.

Because of the irregularities in Earth's rotation, there could be even more leap seconds in our future. "The modeling of the Earth predicts that more and more leap seconds will be called for in the long term, but we can't say that one will be needed every year," Chopo Ma, a geophysicist at NASA's Goddard Space Flight Center and a member of the directing board of the International Earth Rotation and Reference Systems Service, said in a statement.

Comedian John Oliver may have the best take on leap second. The host of HBO's "Last Week Tonight with John Oliver" purchased the Web address SpendYourLeapSecondHere.com , and the site will feature some of the best one-second videos on the Internet.