unruh wrote: > On 2010-02-10, David J Taylor > <david-tay...@blueyonder.delete-this-bit.and-this-part.co.uk.invalid> wrote: >> "David Woolley" <[email protected]> wrote in message >> news:[email protected]... >>> David J Taylor wrote: >>> >>>> I remember the flying of caesium or other atomic clocks round the >>>> world, and that folks had to invoke relativistic corrections. Were >>>> these better than microseconds as well? >>> That's called Navstar (GPS) and GPS position solutions do have to >>> include a general relativity correction to the satellite clocks. >> Not today's GPS, but some forty or more years ago: >> >> http://www.hp.com/hpinfo/abouthp/histnfacts/timeline/hist_60s.html >> >> 1964: >> >> "The highly accurate HP 5060A cesium-beam atomic clocks gain worldwide >> recognition as the "flying clocks" when they are flown from Palo Alto to >> Switzerland to compare time as maintained by the U.S. Naval Observatory in >> Washington, D.C. to time at the Swiss Observatory in Neuchatel. The atomic >> clock was designed to maintain accuracy for 3000 years with only one >> second of error. The cesium-beam standard becomes the standard for >> international time." >> >> I had wondered what accuracy was obtained - i.e. how far was each nation >> out - and whether relativistic corrections had been needed for these >> "flying clock" tests. > > 1 sec/3000years is 1 part in 10^-11. The gravitational redshift is > gh/c^2 (g is gravity acceln on earth, h the height of the flight, and c > vel of light) which is 10^-12 -- ie below ( but not by much) the > accuracy of the clock. The velocity correction is 1/2 v^2/c^2 which is > again about 1 part in 10^12. Ie, both corrections are smaller (but not > much) than the uncertainty in the clock rate. If the plane flew at Mach > 2, rather than well below Mach 1, you could get that velocity correction > up the accuracy and one would have to take special relativity into > account. > > > Since the flight probably lasted say 10 hr, which is 100000 sec, th > eclocks would have been out by about 1usec. Assuming that the clocks > could then have been synchronized, that would mean that US and > Switzerland time have been out by about 1usec. (Why they would fly from > Palo Alto when the time standard is in Washington DC I have no idea).
Actually the Time Standards lab for NIST are half-way up a mountain in Colorado. As a result they have to make corrections to the time to account for the difference between where they are and sea level. It's not USNO. Danny _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
