dUT1

As time correction DUT1 the small irregularity of the earth's rotation is referred to in Geosciences and Astronomy, by the formula

Is defined. This is the UT1 coupled with the Earth's rotation (ie not completely uniform ) timescale and the UTC coupled to the Atomic Time TAI Coordinated Universal Time, which is spread by the time signal radio stations.

The time correction DUT1 is continuously determined by measuring UT1 by methods of astrometry (eg with CCD meridian circle or VLBI ) and compares with the time signal UTC. The difference is formed with the DUT1 polar coordinates x and y of the three earth rotation parameters (ERP).

Because our time system has the average second from 1900 to 1905 to the base and the Earth's rotation has been pushing about 0.002 seconds per day has slowed, an average of 0-3 milliseconds changes DUT1 per day ( usually in the negative direction ): for example, from 20 to may 25, 2005 by -0.6164 -0.6125 seconds to see an exception, it has then to September 2005 to -0.595 s increased - which is rare, but may be due to good models of Geodynamics predicted with sufficient accuracy.

In international agreements of scientific associations ( especially the IUGG and IAU ) and the national metrology institutes specifies that DUT1 no absolute values ​​greater than or equal to 0.9 seconds to accept that the world time scale does not diverge from the astronomical facts: before DUT1 exceeds the absolute value of 0.9 seconds to 30 June or 31 December, a leap second is inserted.