Clocks will add the extra second to keep in sync with Earth's rotation, which gradually slows down over time.
When the dinosaurs roamed Earth our globe took only 23 hours to make a complete rotation. In space, millisecond accuracy is crucial to understanding how satellites orbit.
"SDO moves about 3 kilometres every second. So does every other object in orbit near SDO," said Dean Pesnell, project scientist for SDO at NASA's Goddard Space Flight Centre in the US.
The leap second is also key to making sure that SDO is in sync with the Coordinated Universal Time (UTC) used to label each of its images.
SDO has a clock that counts the number of seconds since the beginning of the mission. To convert that count to UTC requires knowing just how many leap seconds have been added to Earth-bound clocks since the mission started.
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