Readers will know that I am into precise timekeeping. Yes, I am a time nut.
We have recently had a few leap seconds (here, here, here, here and here) - Ars Technica has a nice write-up on them and why.
The leap second: Because our clocks are more accurate than the Earth
We've recently been treated to that extra day in February that reminds us that 2016 is a leap year. Introduced by Julius Caesar, the leap day is necessary because the orbital year is not exactly equal to the 365 days of our calendar year. Without the adjustment, this year’s spring-like Christmas would eventually become routine even without climate change. After a few more generations, the snows of July would give way again to sweltering afternoons. Given enough time, the seasons would march across the calendar.
Some more - introducing the Leap Second:
For centuries, we expended ingenuity on creating timekeeping machines that, with ever increasing accuracy, allowed us to track the march of the heavens. Today, our clocks are so precise that it's the Earth that fails to stay in synchrony with them. We need an additional adjustment now and then: the leap second.
This adjustment, obviously, is not made to the planet, but to the human system of time that we have constructed to be our Earthly clock. Called the Coordinated Universal Time and known as UTC, it's equal to the Greenwich Mean Time and serves as the basis for all the world's time zones. UTC is an atomic-precision time but, rather than tick away for eternity without meddling, it's adjusted to reflect the rotational position of the Earth.
Let's say that, in your local time zone, noon marks the Sun’s zenith. With UTC, noon will still mark the Sun's zenith for your descendants. And, to make sure that happens, we need to sporadically insert leap seconds into our years.
A lot more information at the article - our Earth's rotation is not uniform so we have to wait for it to slow down enough to warrant a new Leap Second - they cannot be predicted.
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