Leap Second

Well we’ve all heard of the leap year when every four years we had a day to the calandar.  But this December 31 will be special as an extra second is added to the calandar.

Earth’s trip around the sun – our year with all its seasons – is about 365.2422 days long, which we round to 365 to keep things simpler. But every four years, we add 0.2422 x 4 days (that’s about one day) at the end of the month of February (extending it from 28 to 29 days) to fix the calendar.

Likewise, a “leap second” is added on to our clocks every so often to keep them in synch with the somewhat unpredictable nature of our planet’s rotation, the roughly 24-hour whirl that brings the sun into the sky each morning.

Historically, time was based on the mean rotation of the Earth relative to celestial bodies and the second was defined from this frame of reference. But the invention of atomic clocks brought about a definition of a second that is independent of the Earth’s rotation and based on a regular signal emitted by electrons changing energy state within an atom.

In 1970 two systems were established for telling time: one based upon the rotation of the Earth and one based upon the atom.  Unfortunately, the Earth is gradually slowing down throwing the two time scales out of sync.  So every now and again a second has to be added to the atomic clock to keep things nice and neat.

So don’t forget to set your clocks ahead this New Year’s Eve by a second.  I know, I know it sucks were going to lose a second of drinking and partying this year, but the good news is the change over will occur at 6:59.59 p.m. Eastern time.

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