A single additional second will be added at the end of the month. Image Credit: CC BY 2.0 Derek Key
The final minute of the final hour of December 31st, 2016 will be 61, rather than 60 seconds long.
The time adjustment, which will be applied to countries which use Coordinated Universal Time, is designed to offset the time that has been lost due to the planet's slowing rotation.
"This extra second, or leap second, makes it possible to align astronomical time, which is irregular and determined by Earth's rotation, with UTC which is extremely stable and has been determined by atomic clocks since 1967," the Paris Observatory, which houses the International Earth Rotation and Reference Systems Service (IERS), said in a statement.
"The sequence of dates of the UTC second markers will be: 2016 December 31 23h 59m 59s, 2016 December 31 23h 59m 60s, 2017 January 1, 0h 0m 0s."
By a variety of methods. For example, careful measuring of the passage of time, and understanding the interactions of the Earth, Moon and Sun, and by looking carefully at old fossils (in particular, those which show daily and annual effects, such as tidal rhythmites (layers of sand and silt laid down in estuaries)). It's quite normal and been known to us for more than a century: https://en.wikipedia.org/wiki/Tidal_acceleration
Yeah, no. The relationship isn't quite as direct as that. Nevertheless, there are fossils which show both daily and annual characteristics *, and they show that hundreds of millions of years ago the day was a few hours shorter than it is now, and that as a consequence there were more days in the year. * Tidal rhythmites are fossil deposits of silt and sand from ancient river estuaries. There are layers which show daily tidal changes, while groups of layers show changes over the course of a year. Examples of these from hundreds of millions of years ago show years with 400+ days. But yes, it is ... [More]
Clearly. But an added second is a slight extension of the orbit and the same second each year should correspond with a particular place in the orbit. I hardly find fossils relevant to demonstrating this extra second of lag.
The rotation is a part of the orbit. An extra secod in time means it has slowed or else there wouldnt be time to fit the extra second in and still end up in the sae place.
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