In message , "Nero Imhard
" writes:
>On 2009-10-03, at 23:56, Rob Seaman wrote:
>> It's hard to see this as supporting a position that "Only UTC can be
>> disseminated"...
>
>Does anyone have a clue?
I read it as:
"I won't get invited to the BIPM metrological barbeque if
I advoca
On 2009-10-03, at 23:56, Rob Seaman wrote:
> However, is it a true assertion that currently deployed GPS receivers
> return GPS time significantly more reliably (all those 9's) than they
> do UTC? (Assuming a particular model supports both?)
>
> It's hard to see this as supporting a position that
Quoting Magnus Danielson :
>If the receivers where using L2C they would be able to resolve this from the
>signal, as
it has a 8192 week >wrapping.
But not quite yet. No IIR-M satellite was transmitting the CNAV messages on L2C
until
last week when, as a test, SVN49 started to transmit message t
Rob Seaman wrote:
Tom Van Baak wrote:
when all is said and done). A 12.5 minute down time means your
annual reliability can only be 4 9's, not 5 9's... This is why many
receivers remember the last UTC offset values and warm start with
them if they have only been off a short period of time..
In message <0b8b21eb-dbea-4dec-89c5-f27557f37...@noao.edu>, Rob Seaman writes:
>Tom Van Baak wrote:
>It is clearly aberrant design for any system to ever lie about a
>return value.
Well, "lie" is such a strong word.
I know for sure that both the Motorola UT+ and M12+T in certain a
certain spec
Tom Van Baak wrote:
when all is said and done). A 12.5 minute down time means your
annual reliability can only be 4 9's, not 5 9's... This is why
many receivers remember the last UTC offset values and warm start
with them if they have only been off a short period of time...
Warner
User
On Thu, 8 Jan 2009, Rob Seaman wrote:
>
> The key role that UTC plays in framing the "simple utilitarian inferences
> regarding the world around us" that I mentioned is as a prediction of UT1.
> UT1 itself is only known retroactively.
I still don't know what these inferences are.
Tony.
--
f.anth
Tony Finch wrote:
Such as? I can't think of anything simple enough to count as common
sense
which depends on the relation between UT1 and the various local times.
As with most issues discussed on this list, questions need to be
framed properly before they can be addressed.
The key role
On Wed, 7 Jan 2009, Rob Seaman wrote:
>
> > What common-sense inferences do you have in mind?
>
> Simple utilitarian inferences regarding the world around us.
Such as? I can't think of anything simple enough to count as common sense
which depends on the relation between UT1 and the various local t
Tony Finch wrote:
What do you mean by "stabilized" here? Atomic time is the basis of
our most stable time scales. I don't think perturbing a timescale to
follow the erratic slow-down of the earth can reasonably be called
"stabilizing" it.
Civil timekeeping (the underlying global timescale
In message , Tony Fi
nch writes:
>On Wed, 7 Jan 2009, Rob Seaman wrote:
>>
>> On the other hand, permitting a long delay between events - or rather,
>> between scheduling opportunities for events - risks losing the corporate
>> knowledge to handle the events properly.
>
>The good thing about timezo
On Wed, 7 Jan 2009, Rob Seaman wrote:
>
> On the other hand, permitting a long delay between events - or rather,
> between scheduling opportunities for events - risks losing the corporate
> knowledge to handle the events properly.
The good thing about timezones is the code to implement them and al
On Mon, 5 Jan 2009, Rob Seaman wrote:
>
> Alternately, by relying on shifting timezones, there would be no
> underlying stabilized civil timescale permitting commonsense timekeeping
> inferences by humans.
What do you mean by "stabilized" here? Atomic time is the basis of our
most stable time scal
On Tue, 6 Jan 2009, Adi Stav wrote:
>
> Right. Well, both my memory of the archives and M. Warner Losh's summary
> have uses that need to be aware of UT (actually, I think local sidereal
> time, or ET in some cases, so that have to perform conversions either
> way).
No-one uses ET any more. It has
On Tue, 6 Jan 2009, Adi Stav wrote:
>
> Another suggestion in the same vain: standardize all the time zones of
> the world to two specific dates for starting and ending DST (if they use
> it). Add leap seconds at one of those dates only.
That would require the period of DST to be exactly half the
M. Warner Losh wrote:
I don't think anybody can make any meaningful predictions out 7k
years.
The Sun will still shine. The Earth will still spin. Lunar tides
will continue their billion year trend. A solar second will be
incrementally a bit longer yet than an SI second.
If humans st
In message: <49646f64.11204.11917...@dan.tobias.name>
"Daniel R. Tobias" writes:
: On 6 Jan 2009 at 10:12, Tony Finch wrote:
:
: > Note that there's no need for global co-ordination. Each country (or
: > county) can change when it is convenient for them. The effect would
: > probably
Tom Van Baak wrote:
why in your opinion, are leap seconds OK but leap tenth-seconds, or
leap minutes, or leap hours not OK? Each of these preserve, to one
degree or another, the notion of stationary wrt solar time.
I'll refrain from references to current practice. We often get
tangled i
Adi Stav wrote:
But what do you think about my suggestion of phasing the time standard
every few centuries when the standard's DUT reaches 30 minutes?
Won't it make leap hours workable?
I suspect that none of the factions will welcome repeated
redefinitions of a fundamental standard.
Rob
On 6 Jan 2009 at 10:12, Tony Finch wrote:
> Note that there's no need for global co-ordination. Each country (or
> county) can change when it is convenient for them. The effect would
> probably be a shifting of timezone boundaries in lumps and bumps that
> averages out to the overall DUT1 drift.
Rob Seaman said:
> The leap occurs at midnight UTC on 30 June or 31 December. These
> dates apply west of Greenwich, e.g., we saw the leap second in Tucson
> at 5 pm on New Years Eve. East of Greenwich it is already the morning
> of 1 July or 1 January when the leap second occurs.
I know w
On Tue, Jan 06, 2009 at 11:31:52PM +0100, Nero Imhard wrote:
>
> I believe this to be false. People's tolerance for being some fixed time
> offset (modulo 1 DST hour) away from their "time meridian" has nothing to
> do with their tolerance for this value to drift.
I see. And how would such intol
Adi Stav wrote:
Rob Seaman wrote:
Coordinate leap seconds with leap days. Introduce an integral
number of leap seconds each February 29th. Discuss.
February 29th does not start and end all over the world at the same
time.
This is no different than the end of December or June. In f
This is the part I disagree with. "Global civil time" (the underlying
timescale for the numerous local civil time variants) needs to be
stationary with respect to mean solar time. The requirements for
Rob,
A problem is what defines your "stationary" (what bandwidth)
and what defines "mea
On 2009-01-06, at 22:35, Adi Stav wrote:
I am trying to identify a requirement for civil time having a low
(say,
below 30 minutes) DUT.
I would say that the actual requirement is for DUT to stay within a
small interval. Of course this also implies a low DUT, but debating
the need for a l
On Sun, Jan 04, 2009 at 08:58:29PM -0700, Rob Seaman wrote:
> Here's a notion I don't recall seeing before on the list:
>
> Coordinate leap seconds with leap days. Introduce an integral number of
> leap seconds each February 29th. Discuss.
February 29th does not start and end all over the world
Thank you for the discussion so far.
On Mon, Jan 05, 2009 at 04:31:44PM -0700, Rob Seaman wrote:
> Adi Stav wrote:
>
>> what problems could exceeding the tolerance(s) cause?
>
> Well covered in the archive. For astronomy, 1 second of time is 15
> seconds of arc on the equator. This is a large
Tony Finch wrote:
I think for "real time" you mean "local civil time", and for "civil
time"
you mean "atomic time".
Not precisely, but that's the gist.
In the future that role would be taken by atomic time. Yes it won't
trivially relate to any kind
of local time at any place on earth, lik
- Original Message -
From: "Rob Seaman"
To: "Leap Second Discussion List"
Sent: Tuesday, January 06, 2009 5:30 AM
Subject: Re: [LEAPSECS] Reliability
Tony Finch wrote:
The reason DST exists is to more closely sync our activities to
sunrise.
The reason DST
On Tue, 6 Jan 2009, Rob Seaman wrote:
> To return to a previous point, Tony Finch wrote:
>
> > Note that there's no need for global co-ordination. Each country (or
> > county) can change when it is convenient for them. The effect would
> > probably be a shifting of timezone boundaries in lumps and
To return to a previous point, Tony Finch wrote:
Note that there's no need for global co-ordination. Each country (or
county) can change when it is convenient for them. The effect would
probably be a shifting of timezone boundaries in lumps and bumps
that averages out to the overall DUT1 dr
Tony Finch wrote:
The reason DST exists is to more closely sync our activities to
sunrise.
The reason DST exists is because it has become a self-propagating
cultural meme.
Your April Fool's post on risks may be the most coherent analysis I've
read on the subject. (Not trying to be iro
Zefram skrev:
Magnus Danielson wrote:
They also made a
correction for the accumulate error to restore phase relationships.
Except that this correction was faulty. By the mid 16th century, the
phase relationship between the seasons and the c
Magnus Danielson wrote:
> They also made a
>correction for the accumulate error to restore phase relationships.
Except that this correction was faulty. By the mid 16th century, the
phase relationship between the seasons and the calendar had sh
On Mon, 5 Jan 2009, Rob Seaman wrote:
>
> Is it too much to ask that an attempt be made to describe how the logistics
> would work?
Exactly the same way that current time zones work. Every so often,
jurisdictions that become dissatisfied with their current timezone offset
or DST arrangements becau
On Mon, 5 Jan 2009, Brian Garrett wrote:
>
> However, I believe I can safely say that you time lords need not worry
> about what the general public thinks in regard to having clock time
> match the sun's position in the sky, or the "noon becomes midnight"
> scenario. The unwarshed (sic) masses may
M. Warner Losh wrote:
It also wouldn't be a leap-hour in the UTC time scale, but rather
just a DST without end once in 50 generations.
Is it too much to ask that an attempt be made to describe how the
logistics would work?
Of course, I doubt there'd be more than a couple of these shifts
- Original Message -
From: "M. Warner Losh"
To: ;
Sent: Monday, January 05, 2009 4:26 PM
Subject: Re: [LEAPSECS] Reliability
All other users of time, it is widely agree, basically want everyone
to agree on a time, have the sun basically overhead around noon, and
do wha
Poul-Henning Kamp skrev:
In message <421fb837-f23f-4a16-b6f4-f26d1c58c...@noao.edu>, Rob Seaman writes:
It seems very unlikely that leap day will move from February. People
are fond of February. Also, a leap day at the end of December would
be December 32nd :-)
Which would break incredib
Rob Seaman skrev:
Adi Stav wrote:
We know that human tolerance to DUT is higher than 20 minutes because we
don't usually bother to compensate for apparent solar time. We know that
it is probably not much higher than one or two hours because time zones
generally have about that resolution. We gu
ecs-boun...@leapsecond.com
[mailto:leapsecs-boun...@leapsecond.com] On Behalf Of M. Warner Losh
Sent: Monday, January 05, 2009 7:26 PM
To: leapsecs@leapsecond.com; sea...@noao.edu
Subject: Re: [LEAPSECS] Reliability
In message:
Rob Seaman writes:
: Adi Stav wrote:
:
: > what problems
In message:
Rob Seaman writes:
: Adi Stav wrote:
:
: > what problems could exceeding the tolerance(s) cause?
:
: Well covered in the archive. For astronomy, 1 second of time is 15
: seconds of arc on the equator. This is a large error (colossal for
: some purposes). It doesn'
Adi Stav wrote:
what problems could exceeding the tolerance(s) cause?
Well covered in the archive. For astronomy, 1 second of time is 15
seconds of arc on the equator. This is a large error (colossal for
some purposes). It doesn't appear that any other industry has
actually performed
On Mon, Jan 05, 2009 at 09:39:28AM -0700, Rob Seaman wrote:
>
> Lower limits are hard to pin down. Human tolerance on a particular day
> is not the same thing as the tolerance over a year or a lifetime.
> Straining a tolerance for one human is not the same as straining it for 6
> billion. Hu
In message <421fb837-f23f-4a16-b6f4-f26d1c58c...@noao.edu>, Rob Seaman writes:
>It seems very unlikely that leap day will move from February. People
>are fond of February. Also, a leap day at the end of December would
>be December 32nd :-)
Which would break incredibly badly thought out fils
Adi Stav wrote:
We know that human tolerance to DUT is higher than 20 minutes
because we
don't usually bother to compensate for apparent solar time. We know
that
it is probably not much higher than one or two hours because time
zones
generally have about that resolution. We guess that it is
Rob Seaman wrote:
>Also, a leap day at the end of December would
>be December 32nd :-)
Only if there were no February 29. My point is that the leap day appears
to be at the end of the year if you don't bother with months and just
use day-of-year. Just as the idea that February 29 is the leap d
Zefram wrote:
Rob Seaman wrote:
Coordinate leap seconds with leap days. Introduce an integral
number of leap seconds each February 29th. Discuss.
There's also a risk that the lower frequency of leaps would
exacerbate the psychology of leap seconds being an infrequent event.
Countered
On Sun, Jan 04, 2009 at 08:58:29PM -0700, Rob Seaman wrote:
> Adi Stav wrote:
>
>> Then why 4 seconds? Because they could be predicted a decade in
>> advance? Isn't that putting the cart before the horses?
>
> Yes, indeed. You asked a question. I provided a guess. Personally, I
> think the c
Rob Seaman wrote:
>Coordinate leap seconds with leap days. Introduce an integral number
>of leap seconds each February 29th. Discuss.
That would mean bigger leaps. I think a 62-second minute (when most
minutes are of 60 seconds) is too great a disuniformity. It would also
exceed the capacity
Steve Allen wrote:
On Sun 2009-01-04T20:58:29 -0700, Rob Seaman hath writ:
Here's a notion I don't recall seeing before on the list:
Coordinate leap seconds with leap days. Introduce an integral
number of leap seconds each February 29th. Discuss.
This ignores the existing operational sys
On Sun 2009-01-04T20:58:29 -0700, Rob Seaman hath writ:
> Here's a notion I don't recall seeing before on the list:
>
> Coordinate leap seconds with leap days. Introduce an integral number
> of leap seconds each February 29th. Discuss.
This ignores the existing operational systems, and in partic
Here's a notion I don't recall seeing before on the list:
Coordinate leap seconds with leap days. Introduce an integral number
of leap seconds each February 29th. Discuss.
Adi Stav wrote:
Then why 4 seconds? Because they could be predicted a decade in
advance? Isn't that putting the car
I've put the attachment online as I should have in the first place:
http://iraf.noao.edu/~seaman/images/HowLongIsADay.pdf
Nice.
Thanks!
- Jonathan
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/l
On Sun, Jan 04, 2009 at 08:36:31AM -0700, Rob Seaman wrote:
> Adi Stav wrote:
>>
>> I'm trying to understand this position. I have a question.
>
> I appreciate both the question and the polite way it was asked :-)
Thanks for that, and for your answer :)
> I remain flabbergasted that of all the po
Poul-Henning Kamp wrote:
Nobody is "dispensing with mean solar time", you will always be able
to calculate it if you want to.
Just as you are now able to calculate TAI from UTC :-)
The issue, of course, is in details.
By redefining UTC, the ITU proposal would require rewriting our
extensi
Our humble and long suffering moderator informs me that this message
bounced a few days back since the attachment was too big. My
apologies, since my more recent messages were predicated on folks
having seen this plot.
I've put the attachment online as I should have in the first place:
Adi Stav wrote:
On Fri, Jan 02, 2009 at 08:29:21PM -0700, Rob Seaman wrote:
Civil time is solar time. The rate is the issue, not local offsets.
Let's move past the fantasy that the ITU can redefine timescales
willy-
nilly to serve the requirements of a civilization of mole people, and
rath
On Fri, Jan 02, 2009 at 08:29:21PM -0700, Rob Seaman wrote:
>
> Civil time is solar time. The rate is the issue, not local offsets.
> Let's move past the fantasy that the ITU can redefine timescales willy-
> nilly to serve the requirements of a civilization of mole people, and
> rather addre
In message , Rob Seaman writes:
>While they are debating this, it is a mental model they have about
>timekeeping that guides the discussions. Their mental model clearly
>must include the notion that mean solar time is dispensable - else
>they wouldn't be trying to dispense with it.
Nobody
Tony Finch wrote:
(Um, do we actually know the earth's angular momentum and moment of
inertia to any useful accuracy? I would have thought models would be
based directly on angular velocity since that can be measured more
precisely.)
I think it's wrong to say that a directly measurable va
Tony Finch wrote:
>(Um, do we actually know the earth's angular momentum and moment of
>inertia to any useful accuracy?
Our knowledge of the planets' masses is limited. From watching orbits
we know very precisely the product of each planet's mass with the
gravitational constant. But we only know
On Fri, 2 Jan 2009, Rob Seaman wrote:
>
> So yes, I think the angular momentum of the Earth is more real than the
> observations that might be compiled to generate an estimate for its value.
But the value is an estimate, so if you plug numbers into a model based on
this estimate you are only going
Tony Finch wrote:
I find it odd that you are arguing that the mathematical model of
the earth's orbit and rotation is more real than the observations
from which the model is derived.
Clearly I failed again to make my point.
There are two different uses to which one might put statistics.
On Fri, 2 Jan 2009, Magnus Danielson wrote:
> b...@po.cwru.edu skrev:
> >
> > That's 303*365+97*366=146097 days for an average of 365.2425 days per year.
>
> Your arthmetic describes solar days, but fails to describe the sidereal days.
No, he's talking about calendar years, as opposed to the conve
On Fri, 2 Jan 2009, Rob Seaman wrote:
>
> Mean solar time is highly regular and elegantly simple.
Compared to our clocks it's too irregular.
> Civil timekeeping (even under the ITU proposal) is about the underlying
> diurnal period.
What does atomic time have to do with the position of the Earth
On Thu, 1 Jan 2009, Rob Seaman wrote:
>
> Once more from the top, mean solar time is just sidereal time offset by a
> little bit to make up for the Earth lapping the Sun once a year. Nowhere does
> humanity appear in the equation, just the Earth and Sun and Stars.
No, since an oscillator without
Zefram wrote:
Rob Seaman wrote:
It's the usual familiar layered architecture and the apparent
position
of the Sun is from a higher layer then the - so-called - mean
position.
Sidereal time isn't entirely linear in time either, as we all know.
So if the mean behaviour is the more fundamental
On 2009-01-02, at 18:14, Rob Seaman wrote:
Yes, it's certainly true that sundials show apparent solar time.
Not all! A Bernhardt precision sundial has a specially shaped gnomon
and shows UT or local civil time to precisions well within one minute.
Beautiful things. I wish I had one.
N
_
Hi Richard,
Yes, it's certainly true that sundials show apparent solar time. I
looked into buying or building a state of the art sundial when we
moved into a new house a few years back. The cost can be staggering,
so this was hard to justify, but the state of the art is pretty spiffy
th
Rob Seaman wrote:
>It's the usual familiar layered architecture and the apparent position
>of the Sun is from a higher layer then the - so-called - mean
>position.
Sidereal time isn't entirely linear in time either, as we all know.
So if the mean behaviour is the more fundamental, presumably y
Rob Seaman wrote:
>Apparent solar time is derived from mean solar time, not the other way
>around.
The way I see it, apparent solar time is, in an astronomical sense,
derived from sidereal time, not from mean solar time. Apparent solar
time is just sidereal time minus true anomaly. All three p
Dear Brian,
b...@po.cwru.edu skrev:
From: Rob Seaman
...
Like I keep saying, the mean solar day is trivial to compute from the
sidereal day. Look at it this way, there are "really" 366.25 days per
year. That extra day just gets sliced and diced among all the others.
Nice, now we have ex
> From: Rob Seaman
> ...
> Like I keep saying, the mean solar day is trivial to compute from the
> sidereal day. Look at it this way, there are "really" 366.25 days per
> year. That extra day just gets sliced and diced among all the others.
Nice, now we have extra days!
A "leap year" is ev
On Fri 2009-01-02T00:10:10 -0500, Daniel R. Tobias hath writ:
> What does "mean" mean? Don't be mean about it! :-)
In this particular arena, the accepted meaning of mean has been
changed as it was handed along a chain of names, notably among them,
but not limited to
Ptolemy 150
On 1 Jan 2009 at 20:47, Rob Seaman wrote:
> So the point of that preface is that the meaning of the word "mean"
> depends on the purpose of the exercise.
What does "mean" mean? Don't be mean about it! :-)
--
== Dan ==
Dan's Mail Format Site: http://mailformat.dan.info/
Dan's Web Tips: http
M. Warner Losh wrote:
Rob Seaman writes:
Apparent solar time is derived from mean solar time, not the other
way around.
Can you explain this, since I thought it was the other way around...
We live in an empirical world. When investigating the behavior of a
class of objects (or proces
In message: <96c34d96-8a20-453a-b4a6-b8491287b...@noao.edu>
Rob Seaman writes:
: Apparent solar time is derived from mean solar time, not the other way
: around.
Can you explain this, since I thought it was the other way around...
Warner
Tony Finch wrote:
On Thu, 1 Jan 2009, Rob Seaman wrote:
Mean solar time will outlast artificial clocks and the species that
built them by a factor of something like 5,000,000,000 to 50,000.
Not really, because mean solar time is also artificial and can't exist
without mechanical clocks an
On Thu, 1 Jan 2009, Rob Seaman wrote:
>
> Mean solar time will outlast artificial clocks and the species that
> built them by a factor of something like 5,000,000,000 to 50,000.
Not really, because mean solar time is also artificial and can't exist
without mechanical clocks and telescopes.
Tony.
Tony Finch wrote:
M. Warner Losh wrote:
Time used to be strongly coupled to the earth.
Only because it was the most accurate clock we had. It might still
be the most reliable clock we have but our natural tendency to
optimisation means that isn't the most important consideration.
The h
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