On 2011-12-28, Danny Mayer <ma...@ntp.org> wrote: > On 12/28/2011 12:17 AM, unruh wrote: >> On 2011-12-28, Danny Mayer <ma...@ntp.org> wrote: >>> On 12/24/2011 8:10 PM, j...@specsol.spam.sux.com wrote: >>>> John Hasler <jhas...@newsguy.com> wrote: >>>>>> The open sky nearest the OPERA detector is straight up through 1400m of >>>>>> rock. >>>>> >>>>> Jim Pennino writes: >>>>>> And the easiest open sky to get to is horizontally down the tunnel to >>>>>> the entrance which is next to a freeway. >>>>> >>>>> Yes, the entrance is next to a freeway. The entrance to the LNGS >>>>> facility where the OPERA detector is located is near the middle of the >>>>> 10 km long Gran Sasso highway tunnel. >>>> >>>> The bottom line is that the only thing that is relevant is how easy it is >>>> to get to a GPS antenna with an open view of the sky. >>>> >>>> Everything else is bloviation. >>> >>> GPS is not used for this kind of thing, they are too inaccurate, so it >>> doesn't matter. They use atomic clocks. >> >> No they do not. They use GPS. As has been discussed here gps can be made >> accurate to a few ns. GPS is used by radio astronomers to synchronize >> very long baseline arrays. >> (Yes, I also thought that gps was not accurate enough. I was wrong) > > As a fellow astrophysicist you know that you don't just use GPS for this > like you would finding your way around the streets of Vancouver. This is > way beyond those kind of calculations. Of course in astrophysics even 1 > km is below the noise level...
No idea what you mean. The gps I might use to find my way around the streets of Vancouver does not have a time function at all. I would use a gps with a timing output (PPS) with Sawtooth corrections to get me down to something like 5-10ns precision, making sure I used a GPS that did not have an internal bias. > > Danny _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
