F-ckin Leap Seconds, how do they work?

Peter Lothberg roll at Stupi.SE
Tue Jul 3 22:33:02 CDT 2012


(source http://physics.nist.gov/cuu/Units/second.html )

Unit of time (second)  Abbreviations: CGPM, CIPM, BIPM


       The unit of time, the second, was defined originally as the fraction 1/86 400
of the mean solar day. The exact definition of "mean solar day" was left to
astronomical theories. However, measurement showed that irregularities in the rotation
of the Earth could not be taken into account by the theory and have the effect that
this definition does not allow the required accuracy to be achieved. In order to
define the unit of time more precisely, the 11th CGPM (1960) adopted a definition
given by the International Astronomical Union which was based on the tropical year.
Experimental work had, however, already shown that an atomic standard of
time-interval, based on a transition between two energy levels of an atom or a
molecule, could be realized and reproduced much more precisely. Considering that a
very precise definition of the unit of time is indispensable for the International
System, the 13th CGPM (1967) decided to replace the definition of the second by the
following (affirmed by the CIPM in 1997 that this definition refers to a cesium atom
in its ground state at a temperature of 0 K):

The second is the duration of 9 192 631 770 periods of the radiation corresponding to
the transition between the two hyperfine levels of the ground state of the cesium 133
atom.


If anyone still thinks UT1;

We have a NTP server on Earth (say Washington-DC) and Vint has
extended the Internet to planet Mars, can we use NTP?

(Hints: Looking at the clock on Earth from Mars, you se a satellite
 with a orbit, gravity changes by other plaets, unknown distance,
 unknown orbits and time runs faster on mars than on earth..)


--P



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