Your typical earth day of 86,400 seconds will be extended by one second Tuesday to allow clocks to adjust to our planet's slowing rotation, NASA says.
"Earth's rotation is gradually slowing down a bit, so leap seconds are a way to account for that," said Daniel MacMillan of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
The 'leap second" was first added in 1972 and has been implemented an average of once a year since then, but the last decade has seen the need for fewer adjustments, NASA says.
"Scientists don't know exactly why fewer leap seconds have been needed lately," NASA says. "Sometimes, sudden geological events, such as earthquakes and volcanic eruptions, can affect Earth's rotation in the short-term, but the big picture is more complex."
Watch this NASA video explaining why June 30 will get an extra second:
For ideas on how to spend your extra time, watch HBO's John Oliver's suggestions:
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