Time running out for ‘leap second’ that has kept us in step with our slowing planet

[T]hat [next] change could be the last of its kind for the leap second and for our fiddling with time. Telecommunications organisations and financial groups say the continual adding of leap seconds to computers increases the chances of errors being made. Precisely timed money transactions could go astray or vehicles could be sent tens of metres out of position if they are a second out in their measurement of time. Hence the bid to ban the leap second.

But there’s this – a nit at which I must pick

“However, these new, highly accurate atomic clocks also revealed that the Earth’s rotation is slowing down because of movements within the core of the Earth.

“The rate of change is not constant, however; it fluctuates over the years. Indeed, sometimes it does not slow down at all.”

Any change in mass distribution will contribute to a change in rotation rate because angular momentum will be conserved, but a really big term in all of this is the tidal braking from our interaction with the moon. The other contributions add noise to this, which is why the rotation speed can level off or even increase temporarily.

But since moment of inertia depends on R^2, changes in the core must involve a lot more mass relative to changes on the surface of the earth (from weather patterns and water location, for example) to contribute.

I had linked to an article about the problems with leap seconds some months ago, and the author came and gave a talk at the Observatory this past fall. Hearing details of some of the potential problems was interesting — the issue is that programmers generally don’t think about leap seconds, so how a system will respond is dicey, and as more and more systems rely on automation the odds of a dangerous failure increases.

There are systems that simply shut down at leap-second insertion time rather than deal with the unknown response of the computer code. But leap seconds are inserted at midnight UTC. Most of Europe is partying, without much business going on, or planes in the air. But it’s 4 PM in California, and in the morning in Asia. There’s potential for some serious complications.

The bottom line is that most people don’t care about leap seconds. Dropping them will impact astronomers, and mildly offend our sensibilities when noon on the solstices does not have the sun line up overhead — assuming you are at a longitude where this currently happens. But that’s just it: most of us aren’t. We accept time zones as a compromise between precise astronomical time and coordination and scheduling of our lives. It won’t surprise me if leap seconds are deemed more trouble than they are worth.