radio time code clock error

[Jeroni Paul]

Jeff Liebermann wrote:

I live in a fringe reception area for the german time
signal at 77.5kHz

Spain? According the coverage map at:
http://www.ptb.de/cms/en/ptb/fachabteilungen/abt4/fb-44/ag-442/dissemination-of-legal-time/dcf77/reach-of-dcf77.html
Yes, the signal is probably not very strong and you're in the skywave
only region.

Good observer, yes, Spain. Also the Pyrenees are in the way blocking most ground signal.

and have many clocks that use this signal but because
a marginal reception they do not always sync.

That sounds like the older amplitude modulated system. DCF77 also
transmits a phase modulated signal,
https://en.wikipedia.org/wiki/DCF77#Phase_modulation

I knew about the phase modulated encoding on the signal but I am not sure if any of my clocks use that. The older ones sure do not, time ago I dissassembled the oldest alarm clock and scoped the signal output from its radio board and I could see the 0.1/0.2 sec signal drop.

There is a long wave radio transmitter in France at 162 kHz that carries time information by phase modulation of its carrier:
https://en.wikipedia.org/wiki/Allouis_longwave_transmitter
I find it an efficient way to use existing resources, also you can check for reception by listening with a LW radio.

The curious thing about this is every night I have a different set
of clocks sync, they seem to decide at random when the signal was
good enough.

Kinda sounds like you're getting some local interference. It doesn't
take much computah or switcher noise to trash the signal, especially
when it's weak in the first place. If your devices have a loopstick
for an antenna, they are directional, with the strongest signal
perpendicular to the loopstick. I was having random updates until I
moved my WWVB clock away from several switching power supplies.

Yet, if I had one clock next to a noise source I would expect it to sync less times than the rest. But no, there appears to be a random distribution.

The oldest one is 13 years old and is an alarm clock I check daily,
in these years I have had it three times take an incorrect time/date
probably from interference. It either takes the right time or does
not sync, three times in 13 years seems not bad for the simple parity
bit protection the protocol uses.

It's a bit more than just the parity bit. Some chips require that the
correct time be received successfully more than once before it will
sync. This is a function of the chip design.

That's what I belived, but then how did it receive incorrect data? Did it actually receive the same wrong data twice in a row? The algorithm could also check for a reasonable deviation against the current setting.

I think, however, it is somewhat dangerous to have the clocks sync
at night *after* you have checked they are set correctly

Sorry, but you don't have a choice as to what time to sync.

Maybe a setting to enable sync only during weekends or only when the alarm function is disabled.

 

[Jeroni Paul]

N_Cook wrote:

Have you had the situation of the displayed time jumping by an hour or two?
As an alarm clock, losing synch and drifting a second or two , to a
background quartz crystal clock, is no great problem

I think on one occasion it was several hours off. You could tell it was a wrong bit value as the data would be wrong by a multiple of two.

 

[Jeff Liebermann]

On Mon, 6 Jul 2015 12:03:13 -0700 (PDT), Jeroni Paul
<JERONI.PAUL@terra.es> wrote:

Jeff Liebermann wrote:
That sounds like the older amplitude modulated system. DCF77 also
transmits a phase modulated signal,
https://en.wikipedia.org/wiki/DCF77#Phase_modulation

I knew about the phase modulated encoding on the signal but I
am not sure if any of my clocks use that. The older ones sure
do not, time ago I dissassembled the oldest alarm clock and
scoped the signal output from its radio board and I could see
the 0.1/0.2 sec signal drop.

I haven't looked into the situation for about a year. I also don't
know the situation in Europe. To the best of my limited knowledge,
there are no commodity clocks and no commodity chips being made that
use phase modulation, in the USA. The technology appears to be owned
by Everset, which has done absolutely nothing for several years. I
could find no distributor that carries their chips. My previous
requests for samples, pricing, and delivery were ignored:
<http://eversetclocks.com>
If you find a consumer grade WWVB chip or receiver that do BPSK, I
would be interested.

There is a long wave radio transmitter in France at 162 kHz that carries time information by phase modulation of its carrier:
https://en.wikipedia.org/wiki/Allouis_longwave_transmitter
I find it an efficient way to use existing resources, also you can check for reception by listening with a LW radio.

<https://en.wikipedia.org/wiki/TDF_time_signal>
I'm not sure, but might be able to take the demodulated output of a
162 KHz receiver, and feed it to a decoder made for DCF77, and get
accurate time updates. I searched with Google and found nothing in
the way of a consumer grade DCF time clock.

You can probably get better info from the Time-Nuts mailing list:
<https://www.febo.com/pipermail/time-nuts/>

Yet, if I had one clock next to a noise source I would expect it to
sync less times than the rest. But no, there appears to be a random
distribution.

Nope. WWVB sends the time code at the rate of 1 bit/second (1 baud).
One frame is 60 seconds. Hopefully, the European systems are similar.
<http://www.nist.gov/pml/div688/grp40/wwvbtimecode.cfm>
All it takes is one noise hit every 60 seconds, and you'll receive
nothing. If your local noise source is intermittent or random, then
it's more a matter of timing and bad luck that will determine if the
clock decodes anything useful.

It's a bit more than just the parity bit. Some chips require that the
correct time be received successfully more than once before it will
sync. This is a function of the chip design.

That's what I belived, but then how did it receive incorrect data?

Good question. I don't know. The only time I've seen an incorrect
display was when I was building a WWVB emulator and spraying garbage
data everywhere:
<http://www.instructables.com/id/WWVB-radio-time-signal-generator-for-ATTINY45-or-A/?ALLSTEPS>
However, I've never seen a random erroneous date or time.

>Did it actually receive the same wrong data twice in a row?

Very unlikely that it might receive the same garbage successfully
twice in a row but possible. However, note that the redundancy
requirement is totally in the chip uses, which might vary in
programming and capabilities.

The algorithm could also check for a reasonable deviation against
the current setting.

I don't think so. Once it gets a valid time to display, it turns off
the receiver to save battery power. No need to decode more than one
or maybe two frames.

Maybe a setting to enable sync only during weekends or only
when the alarm function is disabled.

Personally, I want a graph of signal strength and SNR over a few days
period. Whether anyone is willing to pay for such a feature is
debatable.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
<hobbs@electrooptical.net> wrote:

On 6/27/2015 10:26 PM, thekmanrocks@gmail.com wrote:
I've got the best time sync source of all, courtesy
the NIST and WWVB!

Second best. They adjust those ones to match that yellow thing up in
the sky.
Cheers
Phil Hobbs

Does the NIST use a sundial for a primary time standard? I realize
that budget cuts have necessitated economy measures, this seems a bit
extreme.

>(We just had a leap second.)

Yep. That felt good. I got one second of extra sleep.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Phil Hobbs]

On 07/07/2015 02:37 PM, Jeff Liebermann wrote:

On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
hobbs@electrooptical.net> wrote:

On 6/27/2015 10:26 PM, thekmanrocks@gmail.com wrote:
I've got the best time sync source of all, courtesy the NIST and
WWVB!

Second best. They adjust those ones to match that yellow thing up
in the sky. Cheers Phil Hobbs

Does the NIST use a sundial for a primary time standard?

In a way, they do. Civil time is adjusted to match mean solar time.

I realize that budget cuts have necessitated economy measures, this
seems a bit extreme.

(We just had a leap second.)

Yep. That felt good. I got one second of extra sleep.

I was awake, advancing science.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[N_Cook]

On 07/07/2015 19:37, Jeff Liebermann wrote:

On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
hobbs@electrooptical.net> wrote:

On 6/27/2015 10:26 PM, thekmanrocks@gmail.com wrote:
I've got the best time sync source of all, courtesy
the NIST and WWVB!

Second best. They adjust those ones to match that yellow thing up in
the sky.
Cheers
Phil Hobbs

Does the NIST use a sundial for a primary time standard? I realize
that budget cuts have necessitated economy measures, this seems a bit
extreme.

(We just had a leap second.)

Yep. That felt good. I got one second of extra sleep.

The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?

 

[Jeff Liebermann]

On Wed, 08 Jul 2015 09:22:02 +0100, N_Cook <diverse@tcp.co.uk> wrote:

The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?

Possibly by consensus. Just make reference measurements on as many
inaccurate sources as possible, average them together, and by the
magic of statistics, the average will be more accurate than any
individual measurement. That's because given a sufficiently large
supply of erroneous data, the errors tend to be in opposite directions
and cancel each other. For example, you could average the noon sight
reading from a huge number of sundials or sextants, and the average
will give you NIST grade accuracy.

If this is a problem for you, just buy one of these:
<https://www.kickstarter.com/projects/846511652/the-worlds-first-true-atomic-wristwatch-the-cesium/description>
and you won't have to worry about the sundials and sextants that the
NIST probably secretly uses for calibration. You'll have a personal
time standard that you can trust. Or, just build your own:
<http://www.leapsecond.com/pages/atomic-bill/>
Once you have an accurate clock, all you need to do is decide which
time standard you want to use (LT, GPS, UTC, GMT, GMAT, GAST, SAT,
TAI, Loran, MST, UT, TDT, TBT, TGC/TBC, etc. This might help you
decide how to set your cesium wrist watch:
<http://www.ucolick.org/~sla/leapsecs/timescales.html>
Note that some of these are NOT astronomically based, do not include
leap seconds, were established for political reasons, and don't agree
with other standards. For example, the current differences between
UTC, GPS, and TAI at:
<http://www.leapsecond.com/java/gpsclock.htm>
Also, please note that all of these standards were created and are
managed by various committees, and we all know how ineffective a
committee can be at getting things right.

Perhaps you should just get a wrist sundial:
<https://www.google.com/search?q=wrist+sundial&tbm=isch>
One can't trust the time gods to get it right:
<http://802.11junk.com/jeffl/crud/GPS-vs-UTC.jpg>



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Clifford Heath]

On 08/07/15 18:22, N_Cook wrote:

On 07/07/2015 19:37, Jeff Liebermann wrote:
On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
hobbs@electrooptical.net> wrote:
(We just had a leap second.)
Yep. That felt good. I got one second of extra sleep.
The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?

They don't call it "Coordinated Universal Time" (UTC) for nothing.

My wife is a manager at Australia's National Measurement Institute,
and works directly with the local "Time Lord" who's ultimately
responsible for one of the six atomic clocks that are used to determine
UTC. He's a nice bloke, too.

Of course, nothing in this would allow us to detect a systematic
slow-down in time itself, but if the effect was undetectable, how would
it matter? As long as everything slowed down at the same rate, it would
cause no effect that we could measure. So we compare the six clocks as
they wander around each other, and we try to pick a mean line between
them and call that line "coordinated time". And of course we do research
to try to find a way to build a clock which tracks that mean line better
than current ones do, which is how we got to where we are.

Clifford Heath.

 

[Phil Hobbs]

On 7/8/2015 4:22 AM, N_Cook wrote:

On 07/07/2015 19:37, Jeff Liebermann wrote:
On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
hobbs@electrooptical.net> wrote:

On 6/27/2015 10:26 PM, thekmanrocks@gmail.com wrote:
I've got the best time sync source of all, courtesy
the NIST and WWVB!

Second best. They adjust those ones to match that yellow thing up in
the sky.
Cheers
Phil Hobbs

Does the NIST use a sundial for a primary time standard? I realize
that budget cuts have necessitated economy measures, this seems a bit
extreme.

(We just had a leap second.)

Yep. That felt good. I got one second of extra sleep.



The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?

It's a specific case of a very general problem, namely how to estimate
and control systematic errors in a measurement. Generally speaking, if
your hydrogen maser and your neighbour's caesium clock and your Russian
brother-in-law's Bose-Einstein condensation agree, you can be pretty
confident. Otherwise it's a real headache.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

Clifford Heath: The biggest variant here is the planet
itself. Earth is slowing down, overall, at a more rapid
rate than any of the world's atomic clocks are speeding
up or slowing down. It's why an "ephemeris" second is
inserted every so many years.

 

[Clifford Heath]

On 09/07/15 20:54, thekmanrocks@gmail.com wrote:

Clifford Heath: The biggest variant here is the planet
itself.

No, the planet is not changing the rate at which time passes, and it's
not affecting our ability to measure time.

Earth is slowing down, overall, at a more rapid
rate than any of the world's atomic clocks are speeding
up or slowing down. It's why an "ephemeris" second is
inserted every so many years.

Yes, but that has nothing to do with how we improve our ability to
measure time. Remember I was responding to N_Cook's comment:

"The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?"

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately.

 

[Clifford Heath]

On 10/07/15 11:14, Jeff Liebermann wrote:

On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
no.spam@please.net> wrote:
The fun starts when tracking spacecraft in otter space.

Awesome. Are there any Youtube videos of spacecraft in otter space?
I do love otters, they're my favourite creatures.

 

[Clifford Heath]

On 10/07/15 12:07, Phil Hobbs wrote:

On 7/9/2015 9:14 PM, Jeff Liebermann wrote:
It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).
You'd be off by 17 km. Is Voyager 1's position known to that accuracy?
Didn't think so.

And yet if you were aiming at Pluto via a slingshot around Venus, you
don't want to be 17km off on approach to Venus. I can't do the math, but
I suspect it's rather closer to 17cm.

 

[Clifford Heath]

On 10/07/15 13:33, Jeff Liebermann wrote:

On Fri, 10 Jul 2015 02:58:26 +1000, Clifford Heath
no.spam@please.net> wrote:
On 10/07/15 11:14, Jeff Liebermann wrote:
The fun starts when tracking spacecraft in otter space.
Awesome. Are there any Youtube videos of spacecraft in otter space?
I do love otters, they're my favourite creatures.
Photos of some otter space otters:
https://www.google.com/search?q=space+otter&tbm=isch
I don't really like otters.

I've only seen sea otters once, on a visit to Monterey.
I guess you also are more fond of animals you don't have locally.

The common otter is super cute. One day, I want to learn how to ot.
it looks like fun.

 

[Jeff Liebermann]

On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
<no.spam@please.net> wrote:

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately.

It might help to mention that we have two types of time accuracy. One
is sidereal time, where 12AM on Jan 1 is astronomically correct and is
used to aim telescopes on earth. This is where we says "at the tone,
the time will be... (beep). The other is the length of 1 second,
minute, hour, day... year which is a numerical count of how many
wavelengths of light or cycles of atomic gigahertz
vibrations pass during these intervals also known as atomic time.

The problem is that the two systems don't quite coincide. The current
difference between UTC and International Atomic Time (UTC-TAI) is now
36 sec and growing. The recent leap second just made things worse.

The fun starts when tracking spacecraft in otter space. Not only does
one have to deal with relativistic effects, but one also has to use a
time system that is independent of how the earth spins, wobbles, and
thrashes around. It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).

There's quite a bit of detail summarized here including what would
happen if GPS (atomic) time were "harmonized" with local time.
<http://www.ucolick.org/~sla/leapsecs/>
Only the top part is up to date but the old stuff is interesting.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Fri, 10 Jul 2015 02:58:26 +1000, Clifford Heath
<no.spam@please.net> wrote:

On 10/07/15 11:14, Jeff Liebermann wrote:
On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
no.spam@please.net> wrote:
The fun starts when tracking spacecraft in otter space.

Awesome. Are there any Youtube videos of spacecraft in otter space?
I do love otters, they're my favourite creatures.

Yep:
<https://www.youtube.com/results?search_query=otter+in+space>

Photos of some otter space otters:
<https://www.google.com/search?q=space+otter&tbm=isch>

I don't really like otters. Years ago, I was diving off Monastary
Beach in Carmel, CA. There was an otter floating on the surface
sleeping. My dive partner decided to poke the otter with a pole. It
looked down at us, and went back to sleep. However, my partner kept
poking the otter until it became irritated. It dived down under us,
came up, and bit me in the buttocks though my wet suit. It wasn't
much of a bite, but did manage to ruin my day.

These days, I look at them with otter contempt.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Thu, 09 Jul 2015 22:07:57 -0400, Phil Hobbs
<hobbs@electrooptical.net> wrote:

On 7/9/2015 9:14 PM, Jeff Liebermann wrote:
On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
no.spam@please.net> wrote:

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately.

It might help to mention that we have two types of time accuracy. One
is sidereal time, where 12AM on Jan 1 is astronomically correct and is
used to aim telescopes on earth.

Nope. Sidereal time is different from civil (solar) time. The Earth
rotates 365 and change times per year with respect to the Sun, but 366
and (the same) change with respect to the fixed stars. So the two get
out of phase pretty fast.

Sorry, my mistake.

The problem is that the two systems don't quite coincide. The current
difference between UTC and International Atomic Time (UTC-TAI) is now
36 sec and growing. The recent leap second just made things worse.

Well, worse if you don't think that the Gregorian reform was an advance.
Pretty soon the vernal equinox would have been in February.

The Julian calendar was working just fine for 1500 years as everyone
know how to tweak the date so that it matches the solar calendar. That
was fine for farmers and bankers, but didn't do much for the church,
which had the bad taste to celebrate their holidays by the calendar
month and date. Most everyone else used the signs of the zodiac to
set the beginning of the month. That worked well for the GUM (great
unwashed masses) except that the church equated the zodiac with pagan
religions, alchemy and witchcraft, so that wasn't going to work. A
pope previous to Gregory XIII tried to switch the holidays to the
zodiac months (can't find the name) but gave up before going public.
I suspect that Gregory XIII must have had second throughts when he
allowed the astronomers to fix the calendar. At least they named it
after him, so I guess he was happy.

Incidentally, if you want a really screwed up calendar, try the Hebrew
calendar, which adds an extra month every 2 or 3 years, every 7 of 11
years.
<https://en.wikipedia.org/wiki/Hebrew_calendar>
There's nothing like a duplicated month (adar) to create confusion.

Personally I think that civil time is more important than atomic time.
Folks who need to know the difference, do.

If we knuckle under to atomic time in civil life, our version of the
Julian problem is that midnight by the clock will soon start occurring
at sundown. The leap second inconvenience principally affects software
developers (and those who trust them).

I don't see a problem. If every political time standards organization
can have it's own time standard, I see no reason why they can't expand
theirs to a calendar standard. You just pick the calendar that is
appropriate for whatever you're doing. It's not much different than
the US before the railroads, where every town had it's own time and
DST standard.

Yeah, there were some hiccups in 2012.
<http://www.wired.com/2012/07/leap-second-bug-wreaks-havoc-with-java-linux/>
<http://www.wired.com/2012/07/leap-second-glitch-explained/>
I missed the fire drill, but still managed to get wakened by a
customer wanting to know why their backup failed. Stupid me had set
cron to start the backup exactly at midnight. That worked, but one
second later, it started a 2nd backup during the leap second. Why, I
don't know, but that's what the log files showed. I killed both
processes and started over.

The fun starts when tracking spacecraft in otter space. Not only does
one have to deal with relativistic effects, but one also has to use a
time system that is independent of how the earth spins, wobbles, and
thrashes around. It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).

You'd be off by 17 km. Is Voyager 1's position known to that accuracy?
Didn't think so.

I was thinking of it in terms of the change in angular error for the
rotation of the earth.
degrees = 17km/40,075km * 360 degrees = 0.15 degrees
Let's see if that works. Voyager 1 and 2 uses the DSN (deep space
network) with 34 or 70 meter dishes at about 8 GHz. That's about 67dB
gain and a -3db beamwidth of about 0.07 degrees for the 34 meter dish,
and 73 db gain and 0.04 degree beamwidth for the 70 meter dish. Since
the DSN tracks the rotation of the earth, a change of 0.15 degrees
would move the main lobe sufficiently to miss the spacecraft.
<http://www.satsig.net/pointing/antenna-beamwidth-calculator.htm>
<http://www.uhf-satcom.com/misc/datasheet/dh2va.pdf>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Phil Hobbs]

On 7/9/2015 9:14 PM, Jeff Liebermann wrote:

On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
no.spam@please.net> wrote:

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately.

It might help to mention that we have two types of time accuracy. One
is sidereal time, where 12AM on Jan 1 is astronomically correct and is
used to aim telescopes on earth.

Nope. Sidereal time is different from civil (solar) time. The Earth
rotates 365 and change times per year with respect to the Sun, but 366
and (the same) change with respect to the fixed stars. So the two get
out of phase pretty fast.

This is where we says "at the tone,
the time will be... (beep). The other is the length of 1 second,
minute, hour, day... year which is a numerical count of how many
wavelengths of light or cycles of atomic gigahertz
vibrations pass during these intervals also known as atomic time.

The problem is that the two systems don't quite coincide. The current
difference between UTC and International Atomic Time (UTC-TAI) is now
36 sec and growing. The recent leap second just made things worse.

Well, worse if you don't think that the Gregorian reform was an advance.
Pretty soon the vernal equinox would have been in February.
Personally I think that civil time is more important than atomic time.
Folks who need to know the difference, do.

If we knuckle under to atomic time in civil life, our version of the
Julian problem is that midnight by the clock will soon start occurring
at sundown. The leap second inconvenience principally affects software
developers (and those who trust them).

The fun starts when tracking spacecraft in otter space. Not only does
one have to deal with relativistic effects, but one also has to use a
time system that is independent of how the earth spins, wobbles, and
thrashes around. It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).

You'd be off by 17 km. Is Voyager 1's position known to that accuracy?
Didn't think so.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

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[Clifford Heath]

On 10/07/15 19:59, thekmanrocks@gmail.com wrote:

Clifford Heath wrote: "No, the planet is not changing
the rate at which time passes, and it's not affecting our
ability to measure time. "

HOW can you make such a statement???
If the planet is gradually slowing down,
over millions of years as reported, the
period of time from noon to noon(or
midnight to midnight), is getting LONGER.

Whoosh! You completely missed the point.

The reason we know it's getting longer is because
we have clocks that *aren't* slowing down. I was
talking entirely about *how we know* they aren't
slowing down.

Our hyper-accurate master clocks have
to account for that somehow.

No,they don't. They just count the time passing,
and we decide what numbers to assign to the days,
hours, minutes, seconds. The *numbers* are not
the *time*.

"The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately. "

OF COURSE IT DOES!! If our super-accurate
clocks don't account for an inconsistent Earth,
then sunrises, sunsets, and everything else
will start happening later & later by those clocks.

And that is *exactly* what is happening.
That is why we need leap seconds etc, to
adjust the *numbering* to match the planet's
motion. But adjusting the numbering doesn't
make time pass slower or faster.

 

Clifford Heath wrote: "No, the planet is not changing
the rate at which time passes, and it's not affecting our
ability to measure time. "

HOW can you make such a statement???
If the planet is gradually slowing down,
over millions of years as reported, the
period of time from noon to noon(or
midnight to midnight), is getting LONGER.
Our hyper-accurate master clocks have
to account for that somehow.


"Yes, but that has nothing to do with how we improve our ability to
measure time. Remember I was responding to N_Cook's comment:

"The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?" "

"The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately. "

OF COURSE IT DOES!! If our super-accurate
clocks don't account for an inconsistent Earth,
then sunrises, sunsets, and everything else
will start happening later & later by those clocks.
Sunrise in June in Connecticut will come at
5:23, 5:24(Daylight Time)instead of 5:20 as it
has for decades, and sunset - 8:32, 8:33,
instead of 8:30 as it has for years. It's
only adding those periodic seconds that
maintains that symmetry.

That's because of PLANET drift, not clock
drift. And overall, it is slowing down, not
speeding up.