NASA solar observatory to add leap second to master clock

To maintain accuracy, NASA said its missions, including the Solar Dynamics Observatory, or SDO, which continuously watches the sun, will join official clocks around the world in adding a leap second to the final minute of 2016.

On December 31, 2016, official clocks around the world will add a leap second at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC).

Clocks do this to keep in sync with Earth's rotation, which gradually slows down over time. When the dinosaurs roamed Earth, for example, 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 1.9 miles every second," Dean Pesnell, project scientist for SDO at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement.

"So does every other object in orbit near SDO. We all have to use the same time to make sure our collision avoidance programs are accurate. So we all add a leap second to the end of 2016, delaying 2017 by one second," Pesnell noted.

The leap second is also key to making sure that SDO is in sync with the Coordinated Universal Time used to label each of its images.

Designed to help us understand the sun's influence on Earth and Near-Earth space, SDO was launched in 2010.

It 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.

--IANS

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