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30 JUNE LAST A SECOND LONGER
Day June 30, 2015 year will last a little longer than usual because they will be officially added a second, so-called second coordination. The practice of adding a second coordination exists since the year 1972, when international service of Earth’s rotation for the first time added a second to universal coordinated time (UTC).
The Earth’s rotation is gradually slowing, and second coordinate are introduced to harmonize world time with an average solar time, “said Daniel Mcmillan, NASA spaceflight Center in Grinbèlt, Maryland.
Strictly speaking, the day lasts 86400 seconds. In everyday life we use world coordinated time (UTC). UTC is the “atomic time”; duration of one second is based on predictable period of electromagnetic radiation in the cesium atoms. This standard is so reliable that atomic clocks have a margin of no more than one second over 1400000 years.
At the same time, the average solar day — time during which the Earth makes a full revolution around its axis — lasts about 86400.002 seconds. Their duration is growing, because the Earth’s rotation is gradually slowing. Scientists have calculated that the average solar day lasts longer than 86400 seconds at least 1820 year.
Just 2 milliseconds difference at first sight seems quite small. But if this little discrepancy will occur every day for a year “contacts” is almost a whole second. In reality this is not always the case. Although in general the Earth’s rotation slows, the duration of each day is changing in unpredictable ways.
Length of day depends on many factors, mainly atmospheric. Seasonal and even daily weather changes can affect the length of the day by changing it to a millisecond over the course of the year. Among other factors — the dynamics of rotation the Earth’s core (in the long-term), ocean currents, groundwater, ice caps, tides.
Scientists track the speed of Earth’s rotation, using the exact method called “interferometry with long base (VLBI). Measurements shall be carried out by a network of stations located worldwide, and NASA spaceflight Center their coordinates, as well as analyzes the collected data. The current dimensions provide accurate to 0.0000003 seconds (3 microseconds), but Space Geodetic Project NASA is already working on a new method that will measure the speed of rotation of the Earth with an accuracy of no more than 0.00000005 seconds (0.5 microseconds).
From 1972 onwards scientists have added an average one correction seconds per year. Nevertheless, over the past 15 years was only 4. Scientists cannot say for sure why this happens. Sometimes sudden geological events such as earthquakes and volcanoes can change the rotational speed of the Earth in the short term, but the overall picture is much more complicated.
Previous leap seconds have led to some problems with computer hardware, allowing many opponents of this practice. One of the main arguments — the inability to predict the introduction of leap seconds in advance. Nevertheless, the issue of abolition or continuation of adjustment is not expected before the end of second 2015 year.
On materials of nasa.govViewing:-185
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