From Wikipedia: Rotation in Angular Velocity of Earth

Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth's rotation. Atomic clocks show that a modern day is longer by about 1.7 milliseconds than a century ago.

GPS Systems

GPS satellites have atomic clocks on board to keep accurate time. General and Special Relativity however predict that differences will appear between these clocks and an identical clock on Earth.

General Relativity predicts that time will appear to run slower under stronger gravitational pull – the clocks on board the satellites will therefore seem to run faster than a clock on Earth.

Furthermore, Special Relativity predicts that because the satellites’ clocks are moving relative to a clock on Earth, they will appear to run slower.

My question is, using a GPS receiver, and allowing for the accuracy of the timing systems involved, is there a method of detecting this reduction in the angular velocity of the Earth over a short, (weeks or months?) timescale?

I do realise that this velocity detection facility is not built into a standard GPS receiver, but completely ignoring engineering details and concentrating purely on the physics of timing events, can in principle alone, GPS receivers detect this reduction in Earth's rotational velocity, due to the accurate timing mechanisms underlying their operation?

Finally, without any modification to a standard GPS, can anybody think of how I could achieving this, by using, say a well defined ground location on Earth and how would this be reflected on a standard GPS, e.g.? I know it will make my location inaccurate but what other effects may occur?

  • $\begingroup$ Related: physics.stackexchange.com/q/199726/2451 $\endgroup$ – Qmechanic Aug 11 '15 at 18:39
  • $\begingroup$ @Qmechanic mea culpa on this, I gave the OP an erronous downvote and a factual error, so I wrote the above question to hopefully improve the original question. I hope the link you cite will be deleted as it's a duplicate. $\endgroup$ – user81619 Aug 11 '15 at 18:46
  • $\begingroup$ If what you want is to measure the length of the stellar day in SI seconds, you are probably better off simply looking up. That is, doing careful ground-based astronomical observations coupled with a stable enough atomic clock. $\endgroup$ – Emilio Pisanty Aug 14 '15 at 22:32

Yes, see "Measurements of length of day [LOD] using the Global Positioning System" (its persistent Digital Object Identifier is doi:10.1029/96JB01889) and subsequent citing literature. Note that this is not a relativistic effect. LOD is a day-averaged measure of Earth's spinning rate, see Wikipedia for background (LOD variations).

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    $\begingroup$ Thanks for the useful resource, but link-only answers are not accepted on this site. There are several reasons for this: 1) Links die over time, 2) If you extract the relevant information from the link it makes a better answer. Link-only answers get deleted. I would encourage you to put the resource link in a comment if you don't want to write a full answer. $\endgroup$ – DanielSank Aug 16 '15 at 17:48
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    $\begingroup$ @DanielSank The policy in this context is flawed; justice always requires consideration of circumstance. Felipe's answer is an extremely helpful citation of someone who did the actual experiment that AcidJazz described. In addition, (1) DOI links don't die over time. That is, it is much, much more likely that Physics StackExchange flops than that DOI.org flops; (2) It is unlikely that extracting the relevant information would be substantially better than just copying the abstract, which might violate the CC license on this site; (3) Felipe doesn't have the commenting privilege yet, does he? $\endgroup$ – CR Drost Aug 16 '15 at 19:19
  • $\begingroup$ Furthermore, the question was not "how", but "is it possible". $\endgroup$ – Felipe G. Nievinski Aug 17 '15 at 1:21

To a first approximation it would make the longitude of the ground station shift. Assuming the satellites are unaffected by whatever slowed the Earth (ie. tidal forces or seismic activity)

But the only way to get a GPS position sufficiently accurate to see the effect would be to use a differential GPS system which compares the incoming satellite signal to the signal from the same satellite at a known ground point. Which would obviously defeat the effect.


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