Steve Allen wrote:
The plots by Arias indicate how well UT1 could have been predicted
over two and three year intervals for the 40 year interval starting
around 1960. It is based on those plots that I have voiced no
concerns for the pointing of our telescopes if leap seconds were
published
defining a perceived problem out of existence, one could
actually find that a real problem has been defined into existence.
Or perhaps I'm wrong. Demonstrate why.
Rob Seaman
NOAO
Warner Losh wrote:
Actually, every IP does not have a 1's complement checksum. Sure,
there is a trivial one that covers the 20 bytes of header, but that's
it. Most hardware these days off loads checksumming to the hardware
anyway to increase the throughput. Maybe you are thinking of TCP or
Warner Losh wrote:
leap seconds break that rule if one does things in UTC such that
the naive math just works
All civil timekeeping, and most precision timekeeping, requires only
pretty naive math. Whatever the problem is - or is not - with leap
seconds, it isn't the arithmetic involved.
Warner Losh wrote:
Anything that makes the math
harder (more computationally expensive) can have huge effects on
performance in these areas. That's because the math is done so often
that any little change causes big headaches.
Every IP packet has a 1's complement checksum. (That not all
,
but rather transmogrified into a similar requirement to maintain and
convey a table of DUT1 values.
Rob Seaman
NOAO
Ashley Yakeley wrote:
As the author of a library that consumes leap-second tables, my ideal
format would look something like this: a text file with first line
for MJD of expiration date, and each subsequent line with the MJD of
the start of the offset period, a tab, and then the UTC-TAI seconds
Peter Bunclark wrote:
Indeed isn't this Rob's ship's chronometer?
Actually, I think it was Mr. Harrison's. (And Steve Allen has been
basing his arguments more recently on this distinction.) This
healthy debate between astronomical time and clock time has happened
before. The answer is the
permitting liquid water.
Without the Moon, the Earth could nod through large angles, lying on
its side or perhaps even rotating retrograde every few million
years. Try making sense of timekeeping under such circumstances.
Rob Seaman
NOAO
to be approximated while using SI seconds.
Rob Seaman
NOAO
Poul-Henning Kamp wrote:
That's an interesting piece of data in our endless discussions
about how important DUT1 really is...
The point is that by allowing it to grow without reasonable bound,
DUT1 would gain an importance it never had before.
different than 36,000 tenths.
Rob Seaman
NOAO
--
Poul-Henning Kamp wrote:
Rob, If you feel uncomfortable with calling leapseconds
discontinuities, then we can use the term arrhythmia instead.
Which raises the question of why projects requiring an interval time
scale lacking in such arrhythmias would have selected UTC in the
first place.
Jim Palfreyman wrote:
With my time hat on, having time that is discontinuous pains me. It
doesn't make sense in my heart. But at least these
discontinuities are in whole seconds.
Any discontinuities must be regularly done. So they are part of all
computer systems and are tested and used all
Tony Finch wrote:
You need to do so in order to implement an accurate clock, since
the clock produces interval time and you need a way to convert its
output to time of day.
As Steve Allen has pointed out, it is in the nature of a clock to be
reset on occasion. What is NTP but a mechanism for
in civil
timekeeping. In short:
6) Where should the lines of elegant design and rational compromise
be drawn?
Rob Seaman
NOAO
Poul-Henning Kamp wrote:
I seriously don't belive you do equality comparisons at the 1msec
level in real world software. Please provide examples.
You know you're in trouble when PHK and I agree. One would think a
(double precision) floating point epsilon test might be what you
want. In
John Cowan wrote:
I assume you mean 23-hour or 25-hour LCT days? True. It does work
against UCT days, though, since they are uniformly 1440 minutes long.
Not should leap hours replace leap seconds.
I am talking about time intervals; you are talking about periodic
events. Two different things.
Amen!
M. Warner Losh wrote:
And avoiding the ugly 61 or 59 second minutes to define away the
problem...
It was the time lords who decreed that rubber minutes were prettier
than rubber seconds. We're now to skip right over rubber hours to
rubber days? Their aesthetic sense seems strangely
fending
off an absurd non-solution, perhaps it would be better to design from
clearly stated use cases, responsive requirements, coherent risk
analyses, a reasonable deployment schedule, a fair-minded budget.
We're not going to successfully define the real world out of existence.
Rob Seaman
NOAO
M. Warner Losh wrote:
Let's turn the question around. What would the harm be if |DUT1| were
1.1s? 1.5s? 2.0s? Contrast this with the harm and difficulty that
the current 6 month scheduling window affords.
Indeed. Go for it. I look forward to reading your report. Who and
what interests
John Cowan wrote:
It can't possibly be. Nobody can know what a change is going to
cost except those who are going to have to pay for it (or not
pay for it).
Are you really suggesting that the planning of technical projects is
impossible? One might expect some investment of time and money in
?
Excellent questions. Might I suggest that they be appropriately
answered before UTC is removed from life support?
Rob Seaman
NOAO
interlocking cycles of the solar system provide a
unique check on any clock.
Rob Seaman
NOAO
On Dec 17, 2006, at 11:48 AM, Poul-Henning Kamp wrote:
Regarding an intenational treaty as a contract is not only pointless,
it is downright silly.
Regarding me as an expert on international law is what would be
silly :–)
The point was to elaborate, in the context of UTC, on some issues
to this provision of
it now.
Rob Seaman
NOAO
A type of estoppel that bars a person from adopting a position in
court that contradicts his or her past statements or actions when
that contradictory stance would be unfair to another person who
relied on the original position.
On Dec 12, 2006, at 5:56 PM, [EMAIL PROTECTED] wrote:
To avoid such failures in the future, Tom Van Baak has agreed to
take over its management and he is now working on the technical
issues involving the migration.
Thanks for looking into that. Thanks to Tom for accepting another
(nearly)
are
simply one possible mechanism for achieving this. The notion of a
leap hour fails to preserve mean solar time in any practical fashion.
Rob Seaman
NOAO
(http://en.wikipedia.org/wiki/Precautionary_principle).
Rob Seaman
NOAO
, and maybe, just maybe – to a few politicians.
I'd vote, myself, for using a subduction zone for this purpose,
although having a goal of launching our waste into the Sun might
serve to invigorate the space program for a few decades.
Rob Seaman
NOAO
On Dec 4, 2006, at 9:41 AM, Rob Seaman wrote:
Any group of hunter-gatherers who stumble on WIPP and think to raid
it as they will likely have been raiding landfills and other fin de
millénaire treasure troves, will first have to pass the threshold
of being capable of gaining physical entry
On Dec 4, 2006, at 4:27 PM, Ed Davies wrote:
Do you really mean UTC here?
Well, I mean any of the various approximations of Universal Time as a
synonym for Greenwich Mean Time. As continental drift becomes
important, the job gets harder. (But then, to return to the original
topic, PHK
,
declare time-of-day to be distinct from time interval, who are we to
disagree? As the New York State Supreme Court rules in the play:
Since the United States government...
declares this man to be Santa Claus...
this court will not dispute it.
Case dismissed!
Rob Seaman
NOAO
Zefram wrote:
the radian is not a very practical unit.
There's nothing at all wrong with the radian - but there is a reason
calculators let you switch between degrees and radians. Each is best
for particular purposes, just as interval time and time-of-day are
best for different uses. See
Hi Tom,Careful not to confuse rate with acceleration andpropagate a common misconception that leapseconds are due to an acceleration/decelerationeffect (as in "leap seconds are due to the earthslowing down").In fact, leap seconds are simply due to the earthbeing slow. How it got to be "slow" and
John Cowan wrote:
1) We have leap seconds because the Earth rotates more slowly
than once every 86,400 SI seconds.
2) Leap seconds will become more frequent in the future because
the Earth is decelerating.
3) Leap seconds occur irregularly because the Earth's deceleration
is not constant and
John Cowan accepts the blame:
1) We have leap seconds because the SI second is shorter
than 1/86,400 of a mean solar day.
Post in haste, repent at leisure (I've been going with too little
sleep lately, for reasons unknown...) I actually do know that
the earth rotates in less than 1 mean
John Cowan wrote:
I accidentally specified sidereal rather than mean solar days by
using the wording the Earth rotates.
Rotate is as perfectly good a word to use relative to our nearby star
as to the distant ones :-) The solar system is chock full of nifty
synodic
periodicities and
Brian Garrett wrote: the mini-lectures did imply that leap seconds compensate for secular deceleration of the earth rather than seasonally accumulated differences between UTC and UT1. To the extent that I understand the point you are aiming for, this statement conflates two issues: 1) that
We have all been so utterly wrong! The scales dropfrom my eyes (http://www.creation-answers.com):A theory of evolution for the creation of the solar systemseems less than satisfactory in regard that the Earth andMoon appear to generate interrelated time cycles.A prize (well, a beer when next we
Steve Allen wrote:In the news.google this week is a press release for a clock thatautomatically tracks leap seconds.Anybody volunteering to tell these guys that their product is about to be orphaned? Sounds like a lawsuit in the making. Would think the ITU lawyers would be interested in their
On Jul 6, 2006, at 12:46 PM, Brian Garrett wrote:
I was told that the station delays their broadcast in order to
enable on-the-spot editing of objectionable material.
Surely the requirement is to permit review of *potentially*
objectionable material. A time signal is no such thing and need
John Cowan wrote:
I regret to state that this remark appears to me no more than
scaremongering.
Merely hyperbole intended to make a point about the art of crafting
fundamental standards. Obviously I failed to make that point :-)
Why precisely, however, do you regret your inference? If my
Clive D.W. Feather wrote:
March was the first month of the year; look at the derivation of
September, for example.
Makes the zero vs. one indexing question of C and FORTRAN programmers
look sane. I've pointed people to the whole 7, 8, 9, 10 sequence
from September to December on those
John Cowan wrote:
In the cover story, it was used as a final
defense against the Invaders and destroyed by them. In the true
story, it was destroyed because it constituted a hazard, but I
forget exactly how.
Thanks! But not sure true story is the opposite of cover story,
here :-)
Both
On Jun 8, 2006, at 8:08 AM, Clive D.W. Feather wrote:
Rob Seaman said:
Thanks! But not sure true story is the opposite of cover
story, here :-)
I don't think John's referring to Against the Fall of Night
versus The
City and the Stars. Rather, at least in the latter, the official
(cover
On Jun 7, 2006, at 2:01 AM, Clive D.W. Feather wrote:
Actually, the evidence from experiments is that the natural sleep-
wake
cycle is about 27 hours long, but force-locked to the day-night
cycle (it's
easier to synchronise a longer free-running timer to a shorter
external
signal than
Tim Shepard replies:
Also hard to imagine how one gracefully transitions
from one to two sleep cycles a day.
It is already the norm in some places:
http://en.wikipedia.org/wiki/Siesta
Thanks for the chuckle. One is then left wondering whether our far
future, Clarkeian Against the Fall
Ed Davies quoted:The Gregorian calendar provides a reference system consisting of a,potentially infinite, series of contiguous calendar years. Consecutivecalendar years are identified by sequentially assigned year numbers.A reference point is used which assigns the year number 1875 to thecalendar
On Jun 4, 2006, at 9:57 PM, M. Warner Losh wrote:
leap days have a rule, while leap seconds are scheduled.
A schedule and a rule are the same thing, just regarded from
different historical perspectives. The leap day rule will most
certainly have to accommodate scheduling changes over the
On Jun 5, 2006, at 8:45 AM, Warner Losh wrote:Leap days have an iron-clad rule that generates the schedule on whichthey happen. Leap seconds have a committee that generates theschedule on which they happen.Further discussion in this thread calls into question the characterization of "iron-clad
On Jun 5, 2006, at 1:05 PM, John Cowan wrote:
(ObOddity: It seems that in Israel, which is on UTC+3, the legal
day begins at 1800 local time the day before. This simplifies
the accommodation of Israeli and traditional Jewish law.)
I wouldn't call this an oddity, but rather an interesting
On Jun 5, 2006, at 1:38 PM, John Cowan wrote:
I found another spectacular illustration of how massive the difference
between solar and legal time can be. Before 1845, the time in Manila,
the Philippines, was the same as Acapulco, Mexico, a discrepancy of
9h16m from Manila solar time. This was
On Jun 5, 2006, at 2:47 PM, John Cowan wrote:
I'm not sure what you mean by civil time in this context.
I meant whatever we've meant in this forum for the past five years.
For some people, civil time is synonymous with standard time; for
others, it means the time shown by accurate clocks in
On Jun 5, 2006, at 4:05 PM, Rob Seaman wrote:
On the other hand, all I've ever meant by the term civil time is
that time that a well educated civilian sets her clock in order to
agree with other civilians for civilian purposes.
I should clarify this to mean the underlying internationalized
Warner Losh objects:There are several doughty people here who happen to have that opinion, but they abide with us mortals outside the time lords' hushed inner sanctum.I have spent much time explaining why leap seconds cause real problems in real applications, only to be insulted like this.Sincere
-utc.dat will always be in the future.
Non-amusingly, in the alternate no-time-of-day universe, this never
becomes a non-issue for recovering the orientation of Earth-2.
Rob Seaman
National Optical Astronomy Observatory
On May 24, 2006, at 7:25 AM, John Cowan wrote:
Can someone lay out for me exactly what the difference is between
clock precision and clock resolution?
Interesting question. Perhaps it is the distinction between
addressability
and physical pixels that one encounters on image displays and
Only hours ago did I learn of the recent problems with D-Link routers.
Remarkable! Just imagine the logical disconnect at the product
development meetings. The marketing folks emphasizing the highly
desirable feature of NTP compliance and the tech folks tossing a list
of 50 servers into the
On Apr 13, 2006, at 10:41 PM, Steve Allen wrote:Today is one of the four days in the year when Newcomb's_expression_ for the equation of time has a value of zeroand it was Samuel Beckett's hundredth birthday. Leap second as Godot: ESTRAGON: And if he doesn't come?
On Feb 17, 2006, at 12:30 PM, Markus Kuhn wrote:
Clive D.W. Feather wrote on 2006-02-17 05:58 UTC:
However, London Underground does print 24:00 on a ticket issued at
midnight, and in fact continues up to 27:30 (such tickets count as
being
issued on the previous day for validity purposes, and
On Feb 19, 2006, at 1:35 PM, Steve Allen wrote:A few years ago Joseph S. Myers of Cambridge University went through the trouble of scanning a copy of the proceedings of the 1884 International Meridian Conference, and I put the TIFFs online http://www.ucolick.org/~sla/leapsecs/scans-meridian.htmlI
window around midnight - say,
23:59-00:01, or 2 out of 1440 minutes per day. It should be even
easier for NTP and other UTC transport mechanisms to avoid 2 minutes
out of 365+ days.
This isn't the solution to every challenge facing civil time - but it
sure simplifies the search space.
Rob Seaman
On Feb 16, 2006, at 2:06 PM, Markus Kuhn wrote:
While there is a 24:00:00, there is certainly *no*
24:00:00.0001.
That would be 00:00:00.0001 instead.
Says who? Didn't we just burn a lot of calories discussing whether
UTC was a real number or a continuous function? Time does
On Feb 16, 2006, at 4:46 PM, Warner Losh wrote:UTC rules state that the time sequence should be23:59:59.7523:59:60.023:59:60.2523:59:60.5023:59:60.7500:00:00.:00:00.25Well, no. ITU-R-TF.460-4 says nothing whatsoever about the representation of time using sexigesimal notation: "2.2 A
On Feb 14, 2006, at 12:50 PM, Markus Kuhn wrote:
You can, of course, define, publish, implement, and promote a new
version (4?) of NTP that can also diseminate TAI, EOPs, leap-second
tables, and other good things. I'm all for it.
But why are you for it? Before investing large amounts of time
On Feb 14, 2006, at 2:28 PM, M. Warner Losh wrote:UTC time stamps in NTP are ambiguous. TAI ones are not.Requirements should be kept separate from implementation. Whatever the underlying timescale, certain external global requirements apply. Whether NTP or some other implementation properly
/4800) aren't even denumerable with
the length of our week. Why then is a requirement that one minute
out of 800,000 accommodate one extra (or one fewer) second seen to be
such an imposition? Especially when anybody who does find it so can
simply choose to use TAI instead?
Eppur si muove!
Rob
are asserted to be a risk. Does their lack present
fewer risks? Prove it.
Rob Seaman
NOAO
Leap seconds are asserted to be a risk. Does their lack present
fewer risks? Prove it.
No, you prove it. Such rhetorical devices are designed to divide
and separate,
No, my rhetoric really isn't designed for that purpose. And even if
it were so - how does that possibly undermine the idea
On Jan 24, 2006, at 12:50 AM, Peter Bunclark wrote:
I don't think Rob meant the above to be a complete course on
navigation!
...although as a fan of Patrick O'Brian I am qualified not only to
teach navigation, but also the violin and Catalan. You should see me
in a Bear costume.
Good
On Jan 24, 2006, at 8:06 AM, Ed Davies wrote:
James Maynard wrote:
The problem is not that the SI second is not based on a natural
phenonemon (it is), but that the periods of the various natural
phenonema (rotations of the earth about its axis revolutions of the
earth about the sun,
On Jan 24, 2006, at 7:21 AM, Poul-Henning Kamp wrote:I think the crucial insight here is that geophysics makes (comparatively) lousy clocksThe crucial insight is that the Earth is not a clock at all, but rather the thing being timed.and we should stop using rotating bodies of geophysics for
Ed Davies wrote:By "rubber seconds" you, presumably, mean non-SI seconds. What do you mean by "rubber days"? I'd guess you mean days which are divided into SI seconds but not necessarily 86 400 of them.Yes. See for instance:
to convert shipboard
apparent time to local mean time. Subtraction does the rest.
Rob Seaman
NOAO
is the Russian Global
Navigation Satelllite System :-) In any event, one suspects that the
Russians (or the FSU, even more so) would object to its being
characterized as a GPS backup.
Rob Seaman
NOAO
for
either scientists or sailors. Whether we're also selfish is immaterial.
Rob Seaman
NOAO
-SLS is
intended to serve all needs. Rather, we've heard the opposite.
Suspect I'm not alone in being suspicious of any overreaching
solution proffered for all timekeeping situations - sounds like the
definition of a kludge.
Rob Seaman
NOAO
On Jan 19, 2006, at 10:02 AM, Rob Seaman wrote:
How delightful! A discussion about the design merits of actual
competing technical proposals!
Apologies for failing to credit the quotes from Poul-Henning Kamp.
that many deployed systems (of whatever
nature) are naively configured. Is this likely to change overnight?
Rob Seaman
NOAO
that some other data products were unaffected?
So, the issue has been resolved - would likely have been resolved
sooner if a leap second had occurred earlier - and is no longer
directly pertinent to a discussion of future leap seconds?
Well done, Geoscience Australia!
Rob Seaman
NOAO
-round and the media circus
would have moved on.
Rob Seaman
NOAO
I'm glad to see such active traffic on the list - particularly
discussions such as this that are wrestling with fundamental concepts.
On 2006-01-13, Mark Calabretta wrote:
The point is that UTC is simply a representation of TAI.
On Jan 13, 2006, at 4:17 AM, Michael Deckers wrote:
I
On Jan 13, 2006, at 8:05 AM, Ed Davies wrote:
MJD 27123.5 means 12:00:00 on day 27123 if it's not a leap second
day, but what does it mean on a day with a positive leap second?
12:00:00.5?
And we're back to the point in question. The precise issue is the
definition of the concept of a day.
I see Steve Allen has already supplied a thorough answer. Interested
individuals might also scrounge through the list archives (http://
rom.usno.navy.mil/archives/leapsecs.html) since the topic has come up
before. In fact, Demetrios Matsakis speculated on solar system wide
timescales even
What now, Dr. Moebius? Prepare your minds for a new scale... of physical scientific values, gentlemen.Mark Calabretta takes the lazy man's way out and appeals to facts: Here in a topology-free way is what the axis labels of my graph looklike during
On Jan 10, 2006, at 9:17 AM, Peter Bunclark wrote:On Tue, 10 Jan 2006, Poul-Henning Kamp wrote:In message [EMAIL PROTECTED], Peter Bunclark writes: Good grief. MJD is used widely in astronomy, for example in variablility studies where you want a real number to represent time rather than deal with
On Jan 9, 2006, at 12:06 AM, Poul-Henning Kamp wrote:
You yourself defined stage one as TAI with some constant offset
yourself, you can't change definition in the middle of the discussion.
I was attempting to describe your position. In point of fact, I
agree with Tom Van Baak:
You cannot
On Jan 9, 2006, at 12:23 AM, John Cowan wrote:
This is like the day is light and night is dark statement: there
is, at any given location, one and only one sunrise per (solar)
day, no matter what clocks say.
Communication prospers when people's clear meaning is not subjugated
to petty
On Jan 9, 2006, at 1:01 AM, Clive D.W. Feather wrote:
We go through such discontinuities twice a year in most years.
Only the uninteresting daylight saving jumps. UTC remains without
discontinuities above the level of a leap second. If UTC weren't
equivalent to what I call civil time, the
On Jan 9, 2006, at 1:22 AM, Clive D.W. Feather wrote:
At some point, probably around the time that we're seeing an hourly
shift every year, people are going to have to divorce second from
day, or at least re-negotiate the terms of engagement.
By what magic do we believe the issues involved
On Jan 7, 2006, at 11:01 PM, M. Warner Losh wrote:
This would phase in the predictive timeline for leap second
insertions, and would also give the IERS control to end the
experiment if the time horizons exceeded their ability to predict
with confidence.
it would also be completely within the
On Jan 8, 2006, at 4:41 AM, Poul-Henning Kamp wrote:
It sounds to me like BIPM ought to make an Internet service
available which will deliver UT1 to astronomers in a timely fashion ?
Not sure BIPM is necessarily the appropriate agent, but otherwise
agree 100%. Perhaps we should seek other
On Jan 8, 2006, at 5:38 AM, Poul-Henning Kamp wrote:
As I understood it, it was mainly that TAI is a post-factum
postal timescale.
One is left pondering the fact that UTC is now (and would remain
under any changes I've heard suggested) a time scale based on TAI.
What magic makes one
.
Time zones (and the prime meridian?) would race more-and-more rapidly
around the globe.
Perhaps I've misunderstood, but this line of reasoning doesn't appear
to resolve anything.
Rob Seaman
National Optical Astronomy Observatory
On Jan 8, 2006, at 4:04 PM, Tom Van Baak wrote:
You cannot divide timekeeping, time dissemination, into neat stages.
Again. My point is strengthened. This being the case, a requirement
on one flavor of time transfers to others. We will not solve the
problem of creeping complexity and
On Jan 9, 2006, at 12:03 AM, John Cowan wrote:
Each locality decides when and how to adjust both its offset from
TAI and its seasonal transition function (if any), just as it does
today.
Not just as today, see intervening messages.
What we abandon is a universal time tightly synchronized to
Hi Ed,
Poul-Henning Kamp wrote:
What a weird concept...
Why not go the full distance and define a timescale for each
particular kind of time-piece:
and give each of them their own unique way of coping with
leapseconds ?
Ignoring the ridiculous parody - no, it's not a weird
On Jan 7, 2006, at 11:37 AM, John Cowan wrote:Whether we choose to bleed off the daily accumulating milliseconds one second or 3600 at a time, bleed them we must...and even people who loathe the very notion of leap seconds admit this. NO, I DON'T ADMIT THAT. On the contrary, I deny it, flatly,
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