Earth Rotation and Revolution

[David_Simmons]

@Napier

>They use the average of a bunch of cesium clocks to determine the time. I suppose what is meant by 1 in 1016 accuracy is that the maximum variation of any of the clocks from the average is not more that figure

In my understanding, there is averaging of a number of clocks to determine what is broadcast as UTC, and there’s also averaging of several clocks as part of the GPS system to broadcast and use GPS Time, and some plan - might even be complete now - to integrate the two.

But there’s also the cesium fountain clock, which is far more stable than the clocks used as I just described, though it sounds like it might be intended as research equipment or as a prototype next generation standard clock. Since it’s much better than the others, and since averaging increases accuracy only very slowly as n increases (as n^-1/2), I wonder what they compare the cesium fountain clock to in order to get its accuracy. But there must be something - NIST isn’t going to get the 5E-16 claim wrong!

If they use the cesium fountain clock to determine the accuracy of the average of the cesium clock, why not just use the fountain clock to start with?

Acturally the figure 1 in 10[sup]16[/sup] isn’t really a measuremnt error. The time determined by the clocks is exactly the USA time by definition. The accuracy figure is an indication of how confident they are that their clocks are stable. If they all cluster very closely around the average they must be stable over the laong haul.

And, of course, the time is adjusted every so often to keep our time in sync with solar time.

[Nic2004]

“Does anybody really know what time it is? Does anybody really care… about time?”

[David_Simmons]

@Nic2004

“Does anybody really know what time it is? Does anybody really care… about time?”

The time is whatever the Bureau of Standards, or whatever they call it now, says it is.

I think astronomers who combine widely separated telescope outputs are super interested in pretty precise time.