Attila Kinali said:

What do people on Earth do if they live in someplace like Denver that isn't at
sea level.

--
These are my opinions.  I hate spam.

On Fri, 12 Apr 2024 12:09:26 -0700
Hal Murray halmurray@sonic.net wrote:

We do correct for gravitational redshift already.

Until recently, a simple using the simple geo-potential survey
we had, was enough. The gravitational redshift on earth is
approximately 1.1e-16/m. It hasn't been very long that the
uncertainties in the realization of the second got below 1e-15.
So, an uncertainty in the geopotential of a few meters was ok.

I know that in the last decade quite a few labs measured their
local gravitational potential. But I guess, with the upcoming
redefinition of the second, the proliferation of optical
clocks, and the progress we had in gravitational sensors
(quite a few of them coming out of SYRTE in Paris), there is
likely to be a new campaign to measure gravitational potentials
more accurately again, in the next decade.

		Attila Kinali

--
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always
wonder about. And that's why we do research.
-- Kobayashi Makoto

Yes, that statement annoyed me as well..

If you compare the cesium oscillator on the moon with the one on earth, you'll find that the one on the moon is oscillating about 0.0006794 times faster. The only way to keep the two in sync is by appying leap microseconds or leap seconds on a regular basis.

On the moon you can't make an Earth second by dividing your oscillator by 9192631770, you need divide by 91926318480 to get a TAI-compatible second, if my early morning math is correct.

If you do divide by 9192631770, you need 58.7µs per day in corrections to keep in sync with Earth time. 19.8ms per year.

regards,

--
Ruben

isn't at sea level.

Hal,

Everyone uses UTC, which is already corrected for relativistic effects.
That's why clocks in Denver and New Orleans and everywhere else agree.
UTC is not just free running cesium clocks, it's cesium clocks
referenced to "the rotating geoid", meaning elevation, rotation, even
oblation, are taken into account. Otherwise it would be chaos as
everyone with a good clock would disagree on what time it is.

Back to the lunar thread, here's a recent paper on the topic:

"A Relativistic Framework to Establish Coordinate Time on the Moon and
Beyond"
https://arxiv.org/abs/2402.11150
https://arxiv.org/pdf/2402.11150.pdf

/tvb

Hi

The only real issue here is if your time source is on the moon, it will need to
tune far enough to stay locked up. For an OCXO based gizmo, not a big deal.
For something more exotic, the tuning range might or might not be adequate on
an “out of the box” device. I sort of doubt that anybody seriously is thinking about
grabbing a “stock” fountain clock and just shooting it off to the moon …..

Bob

We readjust the bobs on the pendulums to be a bit higher. We add a many millimeters to the column height readings of the mercury barometers. Then we ride bikes to downtown Boulder to meet our friends at NIST for coffee… and maybe ask them how they compensate for altitude, and about their latest cool optical standard, time transfer, and position/navigation projects… then go for a hike to reflect on what we have learned, pick up something to make into supper at the farmers market, and listen to music from either of two excellent community radio stations.

Sent from my iPhone

Hi

Well, there’s some fun math to sort through …. yikes !!!

So, we now have a first order set of math for LTC. Based on all of that, one would guess that things just might change a bit over time. (just as it does for UTC).

Do we get lunar leap seconds?

Yes, it’s really a two part question. First part would be “do we need lunar leap seconds?”. If the answer turns out to be no, then everything stops at that point. Second part would be, even if they are “needed”, based on how much fun they are here on earth, do we force the moon to have them as well? We’re kinda sorta starting from scratch here.

Bob

On 2024-04-13 08:00, Rsec Van der leij via time-nuts wrote:

-58.7 microseconds / day is the mean correction for the selenocenter -
or for an observer arbitrarily far from the Moon in the same orbit as
the Moon.

If you include the red shift from the Moon's gravity at the lunar mean
surface, the mean difference is  -6.481536356e-10  or = -56.0005 micro
sec / day.

My proposal for Lunar Adjusted time is to red shift clocks on the Moon
by the opposite amount, so that the mean rate for lunar clocks matches
the mean rate for TAI. If that is done, the biggest orbital redshift
correction - the equation of the center (i.e., the Moon's eccentric
orbit) - amounts to 479.66719 nanosec over a month on average. In other
words, Lunar Adjusted Time would match TAI to about 1/2 a microsecond.

GPS satellite clocks of course already run on an adjusted time, being
redshifted by 4.46473e-10  or 38.5753 micro sec / day.

Regards
Marshall Eubanks

On 2024-04-13, at 14:00, Rsec Van der leij via time-nuts time-nuts@lists.febo.com wrote:

Make that 0.0006794 ppm faster?
(~ 0.7 ppb)
That is likely to be in the capture range of most clocks...

Grüße, Carsten