> The tidal effects are much smaller than those from position. I don't > think that these effects are visible at the 10-14 or 10-15 level, but > since I don't know what level they are visible at, I can't be sure. > I'm sure that someone on this list, maybe as part of their PhD thesis, > has measured this and can report it :-) > > Warner
Gravitational effects on frequency near the earth are on the order of 1e-16 per meter of elevation. This level is too small to measure directly, but if you separate clocks by say, 1 km, the frequency shift is now 1e-13, which is very measurable. Since no national timing labs are actually at mean sea level they all take altitude into account in their primary standards. Tidal effects (so-called earth tides) are a couple of ten cm over 6 hours and thus down in the 1e-17 range. No one has seen these effects on atomic clocks yet. First, it's just too small to be measured, even with the best optical clocks, but second, the nearby reference clock that you use would also experience the same pull (!) and thus a relative comparison would reveal nothing. /tvb _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.