Square 30, 45, 60 (UT1
) 30, 45, 60 (UT2) 30 (UT3) Reference h [mm] Wallis and Kuo < 7  Bharathan et al.
(20) These seconds are added into UTC in order for it to keep roughly in line with both TAI and UT1
. While TAI is relatively stable, UT1
is calculated in reference to the rotation of the earth.
Reason one can be traced to the original Markowitz/Essen measurement; the atomic second was defined with respect to the ephemeris second, which then served as the SI second, and not with respect to the mean solar second, which forms the basis for UT1
. Ephemeris seconds were thus already slightly shorter than mean solar seconds, and this characteristic was passed along to the atomic second, making the need for periodic leap seconds inevitable.
Another time standard, called Universal Time 1 (UT1
), is based on the rotation of Earth on its axis with respect to the Sun.
(2) CNRS; LAAS; 7 avenue du colonel Roche F-31077 Toulouse Cedex 4 France and Universit'e de Toulouse UPS, INSA, INP, ISAE; UT1
, UTM, LAAS F-31077 Toulouse Cedex 4 France email@example.com
The International Earth Rotation Service (www.iers.org) which is tasked with determining a time scale based on the rotation of the earth UT1
has indeed measured a slowing down of the rotation of the earth.
But ships and planes carried on navigating on Universal Time, or UT1
, which is also popularly known as Greenwich Mean Time.
Yesterday SMD loaded UT1
(Ultra Trencher 1), a remote controlled submersible robot (ROV), on to a ship for delivery to CTC Marine Projects.
The sensor interval was 35 mm between the UT1
and UT2 (UT3 and UT4) and 45 mm between the UT2 and UT3.
One South African series measured breast milk levels of both trimethoprim and sulfamethoxazole among 50 Bantu women treated with TMP/SMX for various infections (including UT1