Leap seconds face judgment day as time lords prepare to vote

It's about time: the General Conference on Weights and Measures looks set to end leap seconds in an effort to reach horological harmony. Since 1972, 27 leap seconds have been added to Coordinated Universal Time (UTC) to keep it in step with the astronomical time scale UT1, which is based on Earth's fluctuating rotation. The proposal would increase the permitted difference between UTC and UT1 from 0.9 seconds to one hour, avoiding leap-second adjustments for centuries. Earth's rotation has also sped up in recent years, raising the possibility of a negative leap second – removing a second rather than adding one. That has never been done before. Experts have estimated a 30 percent probability that global systems will need a negative leap second by 2035 to keep the two time measures in step. That could pose problems for computer systems designed to handle added seconds but not removed ones. Many national bodies support the proposal, which is expected to pass. …