Steve Allen wrote:
>On Thu 2005-08-04T19:30:49 -0700, Scott Moore hath writ:
>
>
>>The point was for retorical argument only. Using TAI, or TAI synced
>>reference as an internal timebase, any computer can calculate the solar
>>time to far greater accuracies than one second.
>>
>>
>
>The underlying problem here is that it is not possible to compute
>"solar time".
>
>The reason that we need leap seconds on an "as needed" basis is
>that "solar time" must be measured by astronomers and geophysicists.
>
>
>
>
There's going to be three times I, as a computer programmer, would have
to be concerned about (please correct me if wrong).
1. TAI, which I am defining here as "a fixed count of seconds or fraction of
a second, which does not have gaps or additions (leap anything).
2. "fixed formula" solar time, such as UT1, which is an extrapolation of
what
the earth is doing right now out into the future.
3. "true solar", which is what astronomers say it is.
(1) is our time base, (2) is what a computer does if left to its own devices
and never updated, and (3) is reality.
My understanding is that (2) will be correct for quite some time to a fair
amount of accuracy.
In any case, a time distribution system such as WWV, GPS, network time,
etc.,
is capable of giving both TAI reference time, and a correction factor to
achieve
(3), so the only real purpose of (2) would seem to be as a fallback
algorithm
to make sure the computers time as presented to users does not fall
significantly
out of step with (3) if it should (for whatever reason) stop receiving
the correction factor.
If I may be so bold, virtually all time nowadays IS from a network derived
source. My computer is being updated from network time, GPS knows what time
it is from satellite data, your cell phone gets time from that network, and
even the lowly table clock gets updated from the cycle counts that get sent
from the power company, which (in the USA at least) they very much have
exact control over. That leaves wrist watches, which nobody expects to be
that accurate in any case.
So, odd as it may seem, we do indeed have the capability to have astronomers
broadcast the time to virtually every timepiece available.
--
Samiam is Scott A. Moore
Personal web site: http:/www.moorecad.com/scott
My electronics engineering consulting site: http://www.moorecad.com
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Good does not always win. But good is more patient.
Received on Thu Aug 04 2005 - 20:03:01 PDT