Leap Second
Ever feel like you need more time? Today you are going to get it – 1 extra second.
Tonight, at 23 hours 59 minutes and 59 seconds Coordinated Universal Time (UTC), an extra second (leap second) will be added to the world’s clock. This is the 24th leap second added to UTC, a uniform time-scale kept by atomic clocks around the world, since 1972.
Why we need to do that?
Because we have two types of timekeeping.
Historically, the second was defined in terms of Earth’s rotation as 1/86,400 of a mean solar day although we know that the Earth’s rotation was not sufficiently uniform as a standard of time. Then in the 1940s, someone invented the atomic clock which defined a much more precise “time” that is independent of our planet’s rotation. So in 1970, an international agreement established these two timescales: one that is based on Earth’s rotation and the other one based on atomic clocks.
The problem here is that Earth’s rotation is gradually slowing down but the atomic clocks do not. So leap second needs to be added to keep the atomic clocks synchronised with Earth’s rotation time within one second of each other.
The International Earth Rotation and Reference Systems Service (IERS) is the organisation which monitors the difference in the two timescales and calls for leap seconds to be inserted or removed when necessary.
Since 1972, leap seconds have been added at intervals varying from six months to seven years, with the last being inserted on December 31, 2005.
Source: US Naval Observatory
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