Re: Atomic Watches


"Guy Macon" <"http://www.guymacon.com/";>
wrote news:nOydnd2wcai1tdPZRVn_vA@xxxxxxxxxxxxxxx

Exactly correct.


I have to excuse a second time for mixing up things.

Yesterday was not my day. To make it more correct today:



Gravity (and speed) slows down the time. Therefore the

time for 9192631770 cycles of Cs 133 differs depending

on speed and gravity of the place, where the atomic clock is

located. The atomic clocks in navigation satellites GPS

does slow down because of 3.87 km/s by 0.000007 seconds

a day. Standard time is defined as inherent time. The atomic

watch in the satellite therefore runs 0,000045 seconds a day

faster then a equal clock on the surface of the earth. The

combination of these two effects makes the clock in the

satellite 0.000038 s/d faster then the one on the earth.



This is about 350000 cycles of Cs 133 per day. Another

example: The difference between the atomic watch in

Boulder, Colorado, USA and the one in Braunschweig,

Germany is 1.6 times 10 exponent -13. The Bureau

International de l'Heure calculates an average time by using

about 250 clocks all over the world. This time is called

Echelle Atomique Libre EAL. It is transformed to Temps

Atomique International TAI by correcting the time average

to the average gravity of sea level of the earth. (almost all

atomic watches are located *above* sea level ;-) In the last

step, the international earth rotation service IERS standard

corrects SI time UTC, if it differs more than 0.9 second

from TAI.



Because gravity is 9.82306 m/s² on the 45. latitude, 9.745

m/s²on the equator and 9,832 m/s² on the poles, just because

of the elliptic shape of the earth, the discussion of >what is

the average sea level< is more important than the error of

10 exponent -15 of today's atomic watches.



I hope, this time everything is written correctly and in

acceptable English. For readers who can understand

German i can recommend:

http://www.ptb.de/de/org/4/44/pdf/sekunde.pdf

including some more information about the accuracy of

atomic clocks.



While searching, which quantity of gravity is the average

for the calculation, I found an other article, in English, but

very long and *very scientific*: >Report of the CCTF

Working Group on the Expression of Uncertainty in

Primary Frequency Standards< can be found here:

http://inms-ienm.nrc-cnrc.gc.ca/qde/reprints/CCTFWG.pdf

Quote: >not organized in a manner to give easy access to an

appropriate level of reassurance for the casual reader< ;-)

Some more detailed information about the influence of

gravity on atomic clocks is found there on pages 24 to 25,

and about other reasons for inaccuracy.



Ralf Wacker

Greetings from the southwest corner of Germany


.

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