DUT1

The difference between UT1 (proportional to the earth's rotation) and UTC (derived from atomic clocks, with leap seconds) from early 1973 to mid-2015

As time correction DUT1 ( D ifference to U niversal T ime 1 ) is in Earth Sciences and Astronomy the rounded on tenth of a second, from IERS fixed and time signal transmitters radiated difference between the measured with atomic clocks coordinated universal time UTC and by the earth's rotation defined world time UT1 designated.

So it applies

DUT1 ≈ UT1 - UTC accurate to 0.1 s.

In it is

• UT1 is the time scale coupled with the earth's rotation (i.e. not completely uniform)
• UTC is the Coordinated Universal Time coupled with the atomic time  TAI , which is broadcast by the time signal radio stations .

The difference UT1 - UTC and the time correction DUT1 is continuously determined by using methods of the UT1 Astrometrie measures (eg with. CCD - meridian circle or VLBI ) and the UTC time signal compares.

Together with the polar coordinates  x and y, the difference UT1 - UTC forms the three earth rotation parameters  (ERP).

Because our time system is based on the middle second from 1900 to 1905 and the earth's rotation has since slowed by around 0.002 seconds per day, UT1 - UTC changes on average by 0 to 3 milliseconds per day  (mostly in the negative direction): for example, from the 20th . by May 25, 2005 from −0.6125 to −0.6164  seconds . As an exception, it then increased to −0.595 s by September 2005 - which is rare, but thanks to good geodynamic models , it can be calculated with sufficient accuracy .

In international agreements of the scientific umbrella associations (in particular the IUGG and IAU ) and the state metrology institutes it was regulated that UT1 - UTC should not assume any absolute values ​​greater than or equal to 0.9 seconds, so that the world time scale does not differ too far from the astronomical conditions different: Before UT1 - UTC exceeds the absolute value of 0.9 seconds at June 30 or December 31, one will leap second inserted.

Responsible for monitoring the Earth's rotation and thus for the determination of UT1 - UTC and DUT 1 is International Service for Earth Rotation and Reference Systems (Engl. International Earth Rotation and Reference Systems Service, acronym IERS ), the current value of DUT 1 every six months in its Bulletin D.

The current value of DUT1 was set in IERS Bulletin D of April 3, 2019 at −0.2 s from May 2, 2019, 0 a.m. UTC; from this point in time it is transmitted with various time signals.

See also

• Delta T
• Atomic clock , mean solar time , time
• Bary center , GPS time
• International Bureau of Weights and Measures

Web links

• Time-Bulletin of the IERS with tabular values (current)
• IERS bulletins
• International ILRS service ( Memento from 23 August 2003 in the Internet Archive )

Individual evidence

1. ↑ Sigmar German, Peter Drath: Manual SI units: definition, implementation, preservation and dissemination of SI units, basics of precision measurement technology . Springer-Verlag, 2013, ISBN 978-3-322-83606-9 , pp. 127 ( limited preview in Google Book search).
2. ↑ IERS Bulletin D Number 140. IERS Earth Orientation Center, April 3, 2019, accessed on January 15, 2020 .