the hell to do about DUT1.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
quantity, one way or another.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
Some days I feel like my shadow's casting me...
In the Fall of 1999, Judah Levine contacted an astronomer regarding
our community's interest in seeing leap seconds continue. The
astronomer contacted the U.S. National Observatory (NOAO), and its
director, or one of his or her minions,
not the seconds, it's how we count them.
Put your O-O glasses on. It is BOTH the attributes AND the methods of
the class called civil time.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
civil danish time was fixes as the mean solar time at 15 east long.
Well, I prefer layering civil time directly on mean solar time, since
anybody can recover it directly from the sky -- but as I just
demonstrated, I'm willing to entertain other possibilities like the
two separate ones in
that one does not exist
and I assert this will become obvious to all in the fullness of time.
Rob
--
On Feb 14, 2008, at 7:07 AM, Tony Finch wrote:
On Wed, 13 Feb 2008, Rob Seaman wrote:
The day is a key concept in our civilization. The mean solar
day is
the natural way to implement
canned goods, and keeping candles and Y2K certified
matches at the ready :-)
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
.
--
On Feb 15, 2008, at 7:48 AM, John Cowan wrote:
Rob Seaman scripsit:
POSIX is indeed a facet of the world we've built. I might argue that
better system engineering practices might have avoided its
limitations
:-) but we have to deal with the technology we've inherited.
Richard P
of my sermon on planning), and
presume that some other system will be commissioned to transmit DUT1.
However, any DUT1 aware code will have to be relayered on the new
system.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http
Do it really matter /what/ timezone you use in Greenland?
According to the CIA factbook, it matters enough that the long but
narrow Greenland is divided into 4 timezones, with the capital UTC -
3. The 56,000 residents enjoy the many benefits of daylight
saving :-) Greenland has a
Have you ever wondered about the origin of words like Solarium,
I'm not sure how productive this discussion will be. The history of a
word in English versus a similar word in another language may be quite
divergent. For English, the dictionary has an origin for solarium
in the early
Something different to discuss regarding real-world timekeeping
requirements. - Rob
--
Al-Chaahad: new concept for young moon sighting verification
Paper 7017-49
Author(s): Mohamed Laoucet Ayari, Univ. of Colorado/Boulder
Hide Abstract
With an estimated two billion people worldwide
I neglected to mention that this is from an SPIE program:
http://spie.org/app/program/index.cfm?fuseaction=conferencedetailexport_id=x13724ID=x13667redir=x13667.xmlconference_id=796763event_id=796182programtrack_id=796772
--
On Mar 3, 2008, at 11:47 AM, Rob Seaman wrote:
Something
of making new policy.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
Brian Garrett wrote:
it would depend on whether you were doing short- or long-term
planning.
Now there is a distinction I can get behind.
Once again, Shaitan is in the details :)
Two for two - you've summed up my entire perspective :-)
- Rob
they didn't exist at the time.
Grep for messages from Mark Calabretta as to why UTC isn't multi-valued.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
augmented by 3m56s to account for annually
lapping the sun.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
a
representation of mean solar time. The repaired clock could be reset
via observation from first principles. Smash an atomic clock. Then
what?
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
On Mar 28, 2008, at 9:12 AM, Poul-Henning Kamp wrote:
But our problems with POSIX may pale soon, when the politically
ram-rodded, 7000 pages long OOXML standard for office and business
documents gets ratified by ISO as a rubberstamp standard.
As far as I know that standard gets none of leap
scheduling cadence for clock
updates of whatever sort. It doesn't take much insight into human
nature to think that a monthly cadence will get more productive
attention than a decadal or millennial cadence.
Rob Seaman
NOAO
___
LEAPSECS mailing list
around as needed is not equivalent to a
coherent plan.
That said, any such system needs to pass through a system engineering
planning process before it can be deemed to be a solution to any
problem. (Because otherwise there will be no clearly described
problem to be solved.)
Rob Seaman
solution is viable for several centuries yet, what is
our hurry?
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
On Mar 28, 2008, at 4:42 AM, Poul-Henning Kamp wrote:
This is exactly the flagday that will make the upgrades to a few
hundered telescopes look like peanuts.
In grad school one of my housemates was a Swedish postdoc with an
inordinate fondness for Jack Lord and Hawaii Five-O
On Mar 28, 2008, at 4:12 PM, Poul-Henning Kamp wrote:
The thing that seems to be widely overlooked by technologists,
possibly by the high-IQ crowd in general, is that Moores law does
not apply to wetware, and consequently, there very much is a fixed
upper limit for how much technology you can
On Mar 28, 2008, at 4:14 PM, Poul-Henning Kamp wrote:
Only if you can convince ISO9000 consultants that there is a
traceability
from this timescale (as distributed by NTP ?) to UTC which forms the
basis of legal timekeeping.
Ahoy! A requirement has been discovered!
. It's certainly a
real issue for some, but is separable from the issues associated
with leap seconds.
It is precisely that UTC is kept stationary with respect to mean solar
time that permits local timezone issues like DST to be separable from
UTC as you describe.
Rob Seaman
National Optical
LEAPSECS own Tony Finch has a couple of time related contributions in
the current ACM Risks Digest, including a cartoon lampooning daylight
saving time:
http://catless.ncl.ac.uk/Risks/25.10.html#subj4
...as well as a more serious DST proposal, quite worthy of our
consideration:
system engineering started in the Nineteenth century and call
any such new timescale International Time.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
M. Warner Losh wrote:
Poul-Henning Kamp writes:
I can live with International Time as a name, but would far prefer
to have it be Terrestial Time, so it names the rock in question.
Or better yet, Earth Terrestial Time or Earth Normal Time or
Commercial Time, since TT already is an
Yeah, I saw that too, but haven't figured out what symbols he's
talking about. I just see the familiar text files. Anybody have
specific links?
Rob
--
On Apr 9, 2008, at 5:07 AM, Richard B. Langley wrote:
-- Forwarded message --
Date: Wed, 9 Apr 2008 07:50:40 +0200
From:
On Apr 9, 2008, at 6:53 AM, Poul-Henning Kamp wrote:
And the interesting one of course is:
http://www.iers.org/plots/FinalsAllIAU1980-UT1-UTC-BULA.png
This is an up to date version of the first figure (labeled figure 3)
from my screed of exactly seven years ago today:
Poul-Henning Kamp wrote:
In message [EMAIL PROTECTED], Rob
Seaman writes:
What clever chap was it who suggested ALWAYS having a leap second at
the end of each month - toggling positive and negative? An actual
leap transition then becomes the omission of a (negative) leap.
Since
systems
systems.
These state transitions may employ some event driven design paradigm.
But these are choices made by an architect, not requirements implicit
in the system.
Rob Seaman
National Optical Astronomy Observatory
--
Begin forwarded message:
From: Odonoghue, Karen F CIV NSWCDD, W13 [EMAIL
This discussion should go to LEAPSECS and leave NTPWG.
I'm copying it over there. Please remove ntpwg from further replies.
POSIX specs for zoneinfo already require enough complexity to handle
the leap seconds, and the mechanisms for updating the zoneinfo files
are well tested. All
temporal moment arm. The effective LOD zero point is in
the nineteenth century, not the 1970's.
Rob Seaman
NOAO
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
Oooh! Today's my birthday. What a lovely gift! Just what I wanted -
one size fits all!
(Though I bet some of you are thinking, You really shouldn't have! :-)
Rob
--
On Jul 4, 2008, at 5:26 AM, Richard B. Langley wrote:
-- Forwarded message --
Date: Fri, 4 Jul 2008
locale :-) (I'll be in Portland, OR next week,
Santa Barbara at the beginning of August, Baltimore in October, Québec
in November.)
Rob
--
On Apr 9, 2008, at 8:45 AM, Rob Seaman wrote:
On Apr 9, 2008, at 6:53 AM, Poul-Henning Kamp wrote:
Should we make an informal bet on when the next leap
, consider the use cases. To
uncover the pertinent use cases, state the problem clearly. Not one
of these things has happened. Hence candidate solutions to this
unstated problem remain an issue of preference, not system engineering.
Rob Seaman
NOAO
magnetic field? Could this
possibly transfer enough angular momentum to affect the Earth's
rotation?
This particular paper is only worth attention due to the dearth of
similar papers.
Rob Seaman
NOAO___
LEAPSECS mailing list
LEAPSECS
.
--
On Aug 28, 2008, at 1:35 PM, Poul-Henning Kamp wrote:
In message [EMAIL PROTECTED], Rob
Seaman writes:
The 222 year period is most likely a meaningless artifact of the
data.
Likely lack of DC removal and/or deficient windowing before running
the FFT I suspect they used.
--
Poul-Henning Kamp
On Sep 15, 2008, at 6:45 AM, Tony Finch wrote:
On Mon, 15 Sep 2008, Rob Seaman wrote:
The only thing natural about the metric system is that humans have
ten fingers and the quadrant of the Earth something approximating
10 megameters.
The latter was an artificial and deliberate design
On Sep 15, 2008, at 8:42 AM, John Cowan wrote:
Rob Seaman scripsit:
I'm not sure I want to encourage this thread :-) but the answer is
precisely that you are positing a human enterprise. Merely by
referring to civilization, you are conjuring vast webs of
connections to natural cycles at all
On Sep 15, 2008, at 9:32 AM, John Cowan wrote:
Rob Seaman scripsit:
I was referring to the Asimov novel - agoraphobe detective and his
positronic partner.
Yes, I know. I forget in exactly which of his thousand or so essays
Asimov coined the phrase planetary chauvinism for the belief
On Sep 15, 2008, at 9:52 AM, John Cowan wrote:
Rob Seaman scripsit:
Decimal and sexagesimal notation persist because over centuries and
millennia lay people have demonstrated the ability to reach a minimal
level of competency. Which is to say that, for whatever reason, they
are better
John Cowan wrote:
What has the Moon to do with it? The connection of the Moon to the
calendar was lost in Julius Caesar's time -- doubtless to great
howling
by the astro{nom,log}ical community.
...and around we go again. This was my shorthand way of referring to
all the issues
On Nov 12, 2008, at 6:30 AM, Rob Seaman wrote:
dawn's early light
This better fits twilight. Perhaps crack of dawn?
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
Poul-Henning Kamp wrote:
Living in a country that legally still uses 'mean solar time on the
15the eastern longitude' I find this very hard to belive.
We have not even come close to eradicating usage of GMT as an
alias for UTC.
Thanks for emphasizing this point.
I think it is safe to say,
Poul-Henning Kamp wrote:And illegal on many systems, including all USGOV owned and operatedsystems.I thought the ITU had treaty status, therefore that they could decree that we all must henceforth wear Goofy watches that run CCW, and that this sober determination would supersede all other laws of
Clive D.W. Feather wrote:
No, it's because there are no applications where people need to say
what would my GPS receiver had said in 1751?. Whereas people do
need to represent older times in (say) POSIX time.
Do they? Example use case from 1751?
Our (familiar) views are rather orthogonal to the comp.risks assertions.
--
On Dec 9, 2008, at 10:50 AM, M. Warner Losh wrote:
In message: [EMAIL PROTECTED]
Rob Seaman [EMAIL PROTECTED] writes:
: Anybody want to volunteer to take a wack at setting the nice folks
at
: the Risks
John Cowan wrote:
The library does not at all do what you think it does.
You are right, of course.
My apologies to Ashley Yakeley.
Rob
___
LEAPSECS mailing list
LEAPSECS@leapsecond.com
http://six.pairlist.net/mailman/listinfo/leapsecs
David Malone wrote:
These two papers, both from the November issue of The Astronomy
Journal, may be of interest to people here.
DOES RELATIVISTIC TIME DILATION CONTRIBUTE TO THE DIVERGENCE OF
UNIVERSAL TIME AND EPHEMERIS TIME?
Gérard Petit et al 2008 The Astronomical Journal 136
On Dec 16, 2008, at 9:07 AM, Poul-Henning Kamp wrote:
http://www.navcen.uscg.gov/cgsic/meetings/48thmeeting/Reports/Timing%20Subcommittee/48-LS%2020080916.pdf
Thanks for posting this - extremely helpful!
On Dec 16, 2008, at 10:47 AM, Poul-Henning Kamp wrote:
Please discontinue use of your
On Dec 16, 2008, at 11:52 AM, Steve Allen wrote:
On Tue 2008-12-16T16:07:30 +, Poul-Henning Kamp hath writ:
http://www.navcen.uscg.gov/cgsic/meetings/48thmeeting/Reports/Timing%20Subcommittee/48-LS%2020080916.pdf
That was before the meeting in Geneva, before China objected.
Ah! Thanks
On Dec 18, 2008, at 4:27 PM, Zefram wrote:
I think the more fundamental issue is that we will, any way round,
need data that relates the two flavours of time. A single clock
reading can't give both types of time in the absence of such
knowledge.
...and wouldn't a description of how
On Dec 18, 2008, at 9:45 PM, John Cowan wrote:
Ah, but will Lunar civil time be mean solar time on Luna?
For many purposes, yes. The Apollo missions were planned to occur in
daylight, for instance. For other purposes, the factor of ~30
contrast between the lunar day and the innate human
On Dec 19, 2008, at 10:34 AM, John Cowan wrote:
Rob Seaman scripsit:
One supposes the lunar synodic period would be divided into 30 parts.
*One* may suppose it, but others have not, such as Manuel Garcia
O'Kelly-Davis, an actual (though fictional) resident of Luna,
describing
Scroll down for my response. Context seemed important.
On Dec 20, 2008, at 11:33 AM, M. Warner Losh wrote:
In message: d754ef5c-767a-4ff0-ac64-6e9543aaa...@noao.edu
Rob Seaman sea...@noao.edu writes:
: Poul-Henning Kamp wrote:
:
: Steve Allen writes:
:
: Please identify
, discussion.
Rob
---
On Dec 20, 2008, at 11:55 AM, M. Warner Losh wrote:
In message: 490a82a4-a8b3-485e-8ded-f9c8adc89...@noao.edu
Rob Seaman sea...@noao.edu writes:
: M. Warner Losh wrote:
:
: Leap-seconds, as implement, are unworkable.
:
: If so, there are worlds of possibilities short
4957dfe1-9c18-4941-aa87-79e5dd429...@noao.edu, Rob
Seaman writes:
Again - why are engineering best practices regarded as an annoyance?
Rob,
They are not, but they are far different from what you think
they are, and they are slavishly adhered to.
Slavishly isn't an adjective to describe best
I'm sure all will appreciate that I decided to cut my detailed reply
short :-) Here in a nutshell is my recipe for success:
1) Define the problem.
2) Design a solution. (Each problem has many possible solutions.)
This is as simple as it gets for the basis of system
Rather than speculating on each other's state of mind with words such
as fundamental misimpression (as in the thread below), it might be
helpful to focus on the actual questions asked.
Consider the iconic issue of timekeeping for trains, one of the
primary drivers for our current standard
Poul-Henning Kamp wrote:
The only person I have heard claim that the problem is not well
understood is you.
The problem is not something cut and dried like:
How do we avoid introducing (or manage, if we can't avoid this)
timekeeping discontinuities into expensive/remote/critical
due process be followed before making a change of
this magnitude.
Due process is the swiftest process.
Rob
--
On Dec 21, 2008, at 3:31 PM, Poul-Henning Kamp wrote:
In message 8cebf8d1-d76a-484b-a5c0-2f31d2bd4...@noao.edu, Rob
Seaman writes:
The problem is rather expressed in a large number
Poul-Henning Kamp wrote:
In message 407eb3f6-55bb-4e60-8d20-c909ea92e...@noao.edu, Rob
Seaman writes:
Consider the iconic issue of timekeeping for trains, one of the
primary drivers for our current standard time zone system. Trains
clearly need to be synchronized with external clocks
Poul-Henning Kamp wrote:
There is one (major) problem: software does not grok leapseconds.
If my car fails to grok gasoline, I fix the car. Leap seconds (or the
equivalent) are simply a fact of life on a tidally slowing orb. If
you wish to eliminate the overhead of managing leap seconds
Poul-Henning Kamp wrote:
In message ec8cc227-dc49-458a-9725-3ce5ddc8f...@noao.edu, Rob
Seaman writes:
You may disagree with his premises, but the request was for
candidates
for completely standalone systems requiring high precision clocks.
No, the request was for systems that could
So many messages, so little time!
M. Warner Losh wrote:
In general, all systems need to be synchronized to human time
because at some point they have to interact with humans.
Right. And human time is synchronized with mean solar time because
we happen to live on the planet Earth. What
Tony Finch wrote:
On Mon, 22 Dec 2008, Rob Seaman wrote:
No. We have been using mean solar time formally since the 19th
century, and informally since we woke each morning to light shining
through
the entrance of the cave.
Apparent solar time is not mean solar time. Remember
:
In message: f0158734-ca0b-4cd1-bb0e-6b0ad31a1...@noao.edu
Rob Seaman sea...@noao.edu writes:
: Tony Finch wrote:
:
: On Mon, 22 Dec 2008, Rob Seaman wrote:
:
: No. We have been using mean solar time formally since the 19th
: century, and informally since we woke each morning to light
(or omission) of an integral number of days in an intercalary event.
The mechanism is clear, the policy is lacking. The ITU proposal is
lacking not just guidance on policy for the equivalent clock issue,
but fails to even speculate on options for a mechanism.
Rob
---
On Mon, 22 Dec 2008, Rob
Poul-Henning Kamp wrote:
Rob Seaman writes:
Right. And human time is synchronized with mean solar time [...]
What do you really mean by Synchronized ?
The sun rises, the sun sets. We care about this in innumerable ways.
Other than that, this is the precise issue we have been debating
Poul-Henning Kamp wrote:
civil timekeeping is equivalent (in the sense of a mathematical
identity) to some stable approximation to mean solar time.
I don't think anybody disputes that.
Ok. Glad to hear it.
Stable approximation implies that a proposal to change UTC includes
a plan for
Poul-Henning Kamp wrote:
I have told you over and over, that if astronomers got their act
together, they would get this upgrade in the blink of an eye if
business which have real money riding on the leap-second could get
rid of them.
Make us an offer. What have I ever said to suggest
Brian Garrett wrote:
As interesting as the continuing theoretical discussions are (or at
least, what I as an interested bystander can comprehend of them), I
think it might be informative to see examples of how the leap second
to be thrust upon us next week is affecting list members'
On Dec 23, 2008, at 9:33 AM, Zefram wrote:
Suppose that people in the future overwhelmingly want local civil
time of day to continue to approximate local solar time of day.
Again, the issue is mean solar time, not local solar time. An
underlying timescale based on mean solar time is what
I wrote:
Whatever the preferences of the ITU, they will discover that it is
simply unacceptable to allow local dates to vary secularly from
civil timekeeping dates.
Tony Finch replies:
Civil time *is* a form of local time.
The question isn't about haggling over terminology. We've had
I wrote:
Historians looking backward want to relate events worldwide and
arrange them into coherent timelines.
Zefram replied:
Yes, they'll want the Olson database.
Precisely. For a scheme such as this to have any chance of working, a
requirement is that it be tightly coupled to a
M. Warner Losh wrote:
How is the Olson database fundamentally different than the
historical data that a future historian would have based on the
measurements of the delta between what we call today TAI and UT1
times? It is just more data for them to swizzle into their
calculations?
I wrote:
The ITU has a responsibility to consider options with a long term
future.
Poul-Henning Kamp writes:
ITU has no such responsibility:
1 The purposes of the Union are:
a) to maintain and extend international cooperation
among all its Member
M. Warner Losh wrote:
Experience has shown that multiple time scales lead to confusion.
The confusion is inherent in the system requirements. There are two
different kinds of timescale. That is a simple fact. How do we deal
with that reality? Wishing one away won't work.
Look at
M. Warner Losh wrote:
Michael Sokolov writes
: M. Warner Losh i...@bsdimp.com wrote:
:
: I know that nobody is proposing rubber seconds today.
:
: Wrong! I am!
I don't think that's a viable thing to do. It would play havoc with
anything except the most low-precision timing applications.
Michael Sokolov wrote:
But civil time *is* a low-precision timing application!
Civil time is not a timing application. It is not an application at
all. Whatever the past or future of civil timescales, these form
infrastructure that applications are built upon. Precision is one of
Poul-Henning Kamp wrote:
Rob Seaman writes:
Focus on the SI second and we see the world through atomic
eyeballs. Focus on the primacy of the definition of the day in
civil timekeeping, and Earth orientation pops out.
Both timescales are necessary.
It is well documented that the SI
My apologies for the long reply. The personal attacks reached a
tipping point. Others should feel free to skip this (as I'm sure they
do all my messages :-)
Poul-Henning Kamp wrote:
Rob Seaman writes:
Just one comment. The requirements for timing applications (of
whatever precision
Poul-Henning Kamp wrote:
Notice the near: the 0° meridian no longe passes through the
transit instrument there.
Steve and Richard have replied with their usual level of precision.
We risk getting lost in the details.
I might just remind folks that one arc second corresponds to 30 meters
away. Sounds like
another good issue to explore to improve the proposal.
Why does the ITU itself appear to dislike GPS?
Rob
---
On Dec 31, 2008, at 10:40 AM, M. Warner Losh wrote:
In message: ea44a9b7-8c68-4b1e-b1d8-0dc35b4e8...@noao.edu
Rob Seaman sea...@noao.edu writes:
: Steve
Just sitting here watching the Nixie tube page ticking along:
http://leapsecond.com/java/nixie.htm
I have Hard Day's Night on the HD for a sound track. Somehow seemed
appropriate.
Dropped by our sysadmin's office earlier. He didn't look too
frantic. One reason (no irony
Poul-Henning Kamp wrote:
Happy new year and leap-second.
Further evidence that average programmers should not be let near
timekeeping:
http://gizmodo.com/5121822/official-fix-for-the-zune-30-fail
Not to discount the bug reported, but there are lots of other more
complex issues with
On Dec 31, 2008, at 4:55 PM, Rob Seaman wrote:
For those that dig back to the depths of the archives of this list
and prior discussions, I should mention that it was Levine who
kickstarted the interest of the astronomical software community in
this issue. JL contacted an astronomer
On Dec 31, 2008, at 5:30 PM, Poul-Henning Kamp wrote:
Further evidence that average programmers should not be let near
timekeeping:
http://gizmodo.com/5121822/official-fix-for-the-zune-30-fail
Slashdot is having fun with this:
I sense a disturbance in the Force... It's as if tens of
M. Warner Losh wrote:
If we must have leapseconds, we must put them on a better schedule
than 'we'll tell you 6 months in advance'.
If one accepts .9s tolerance, we can make our best guess now for
the next 10 years and be very likely to be very close. We'd likely
know after 5 years how
Ashley Yakeley wrote:
Rob Seaman wrote:
They can't be naively automated. The schedule is currently
predictable 6 months in advance. Nobody has objected to a longer
schedule; we're positively giddy to give it a try. NTP is proof of
concept that automation is possible once the schedule
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
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
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
. Forward if you like. A conventional
sundial directly shows
apparent solar time.
-- Richard
Quoting Rob Seaman sea...@noao.edu:
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
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
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.
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
1 - 100 of 646 matches
Mail list logo
