NASA's SDO Adds Leap Second to Master Clock
https://www.nasa.gov/...re/goddard/2016/space-timekeeping-nasas-sdo-adds-leap-second-to-master-clock
On Dec. 31, 2016, official clocks around the world will add a leap second just before midnight Coordinated Universal Time — which corresponds to
6:59:59 p.m. EST. NASA missions will also have to make the switch, including the Solar Dynamics Observatory, or SDO, which watches the sun 24/7.
"SDO moves about 1.9 miles every second," said Dean Pesnell, the project scientist for SDO at NASA's Goddard Space Flight Center in Greenbelt,
Maryland. "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."