Indian timekeepers add leap second to sync with Earth's spin

NASA missions, including the Solar Dynamics Observatory (SDO) which watches the Sun, will join timekeepers around the world to add a leap second to its clocks, just before midnight on New Year’s Eve.
●    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.
●    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.
●    When the spacecraft wants to provide a time in UTC, it calls a software module that takes into consideration both the mission’s second count and the number of leap seconds – and then returns a time in UTC.