(WHTM) — Well, it seemed like a good idea at the time…
For decades we have measured the length of a second in two ways. In Astronomical timekeeping, one second equals the amount of time it takes to complete one rotation (midnight to midnight, noon to noon, or whatever start/end point you care to use) divided by 86,400, there being 86,400 seconds in a day, more or less.
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In atomic timekeeping, a second lasts for 9,192,631,770 vibrations of a cesium 133 ion. This also works out to 86,400 seconds in a day, more or less.
With the help of a lot of high-end math, the two timescales are combined to create Coordinated Universal Time (UTC).
The two systems match up almost exactly-but that “almost” causes no end of mischief. It seems the earth’s rotation is gradually slowing down, which means atomic time slowly pulls ahead of astronomical time.
So in 1972, the first leap second occurred. The idea is simple enough – stop the atomic clock for one second so the astronomical timekeeping can catch up. As of this writing, 27 leap seconds have been added.
Now, adjusting time by one second isn’t a big deal for us. (Daylight Savings Time is another matter.) computers, however, are rather finicky beasts that can crash if their internal clocks have to make an adjustment. (we’re talking about something much deeper in the circuitry than just resetting the main screen time display.) And since just about everything more complicated than a windup alarm clock runs on a computer these days, you never know what sort of catastrophe a leap second will trigger. In both 2012 and 2017, for instance, leap seconds knocked a lot of IT companies offline.
It would help if the leap second was a regular thing, but in practice, a leap second is added whenever the difference between astronomical time and the atomic time nears 0.6 seconds. Since there’s no way to predict exactly when that will happen, spacing between leap seconds is…irregular.
And then, as if things weren’t crazy enough, starting in 2020 the Earth’s rotation sped up. The year contained the 28 shortest days since 1960. (We’re talking milliseconds here, but still…) June 29, 2022, was the shortest day since atomic clocks started measuring time. There are theories about why this is happening – melting glaciers, earthquakes, movement of the north and south poles, to name a few – but nobody really knows. It raised the possibility, though, that sometime in the near future we might have to subtract leap seconds to balance things out.
In response to these Chronology conundrums, on Friday, November 18, members of the International Bureau of Weights and Measures, Or BIPM (Bureau International des Poids et Measures) voted to discontinue the use of the leap second starting in 2035 and continuing until 2135. UTC will continue, but atomic Time and astronomical time will diverge. By 2135 this separation could be as much as a minute. The thinking – or perhaps we should say the hope – is that by then we’ll have come up with a better way of dealing with the problem, either by making computers more flexible about accepting timestamping changes or by creating a better way to measure time entirely.