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

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