Determination of the placement of the first pps
As I am, as Heinlein would say, but an egg in terms of time-nuttery,
perhaps someone could point me toward some history in order to help answer
a question recently posed to me.
At what point was the original global 1pps leading (trailing?) edge
defined/distributed and to what was (is) it referenced? Someone, someplace,
had to give the original time 'hack', no?
I found I could talk about all the wonderfullness of GPSDOs, rubidiums,
ocxo's and the like but couldn't answer that simple question with much more
depth than 'NIST does it for the US' or 'you pull it off of the GPS'.
Thanks,
Bob
Hi
The original location of the PPS was from astronomical data. That's still
what ultimately steers UTC.
More precisely, for the US, there's a telescope at the Naval Observatory
that watches the sun as it comes overhead. The point it hits this or that
mark on the telescope tells you what the official solar time is (after some
math). The current one has been in place since the late 1800's, and it's
still in use.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Bob Bownes
Sent: Friday, January 20, 2012 12:23 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Determination of the placement of the first pps
As I am, as Heinlein would say, but an egg in terms of time-nuttery,
perhaps someone could point me toward some history in order to help answer
a question recently posed to me.
At what point was the original global 1pps leading (trailing?) edge
defined/distributed and to what was (is) it referenced? Someone, someplace,
had to give the original time 'hack', no?
I found I could talk about all the wonderfullness of GPSDOs, rubidiums,
ocxo's and the like but couldn't answer that simple question with much more
depth than 'NIST does it for the US' or 'you pull it off of the GPS'.
Thanks,
Bob
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To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Fri, Jan 20, 2012 at 9:30 AM, Bob Camp lists@rtty.us wrote:
Hi
The original location of the PPS was from astronomical data. That's still
what ultimately steers UTC.
More precisely, for the US, there's a telescope at the Naval Observatory
that watches the sun as it comes overhead. The point it hits this or that
mark on the telescope tells you what the official solar time is (after some
math). The current one has been in place since the late 1800's, and it's
still in use.
It's a transit telescope (one that looks up at the local meridian) but
they don't use the sun. It looks at every start that passes in front
of it, thousands of them every night. Then they reduce the data by
knowing the exact location of every star and the time is pasted
directly overhead. This way they get thousands of measurements every
day. If you use the Sun you get only one per day.
A transit solar scope would be a fun Time Nut project. I think a
primitive one would be a photo cell and a length of wire. Measure the
time when the shadow of the wire sweeps across the cell. The trouble
is that with only one measurements per day it would time years to
build up uSec level data. Even if you placed the cell behind a pin
hold mask and used a fine piano wire, shades and baffles and so on.
This is the telescope that is currently used to measure Earth rotation
http://www.nofs.navy.mil/about_NOFS/telescopes/fastt.html
--
Chris Albertson
Redondo Beach, California
On Mon, 23 Jan 2012 08:43:01 -0800
Chris Albertson albertson.chris@gmail.com wrote:
It's a transit telescope (one that looks up at the local meridian) but
they don't use the sun. It looks at every start that passes in front
of it, thousands of them every night. Then they reduce the data by
knowing the exact location of every star and the time is pasted
directly overhead. This way they get thousands of measurements every
day. If you use the Sun you get only one per day.
Not to mention the solar noon varies by +/- 15min over the year
(don't ask me how this is called...old knowledge from my high school days)
A transit solar scope would be a fun Time Nut project. I think a
primitive one would be a photo cell and a length of wire. Measure the
time when the shadow of the wire sweeps across the cell. The trouble
is that with only one measurements per day it would time years to
build up uSec level data. Even if you placed the cell behind a pin
hold mask and used a fine piano wire, shades and baffles and so on.
Why not use a real telescope with a CCD and get more reliable data?
A friend of mine is into hobby astronomy and uses special type CCDs
for it (ie not even the hobbist look directly into the telescope anymore).
I guess it shouldn't be too hard to rig up some gear, a PC that collects
the pictures at precise instances and calculates the ephemeris time to
UTC/GPS difference. The only issue is that you'd need to put that telescope
somewhere with little light polution, otherwise you'll only get the brightest
stars.
Attila Kinali
--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
Hi
I think the key point is that they are still using a gizmo made in the
1800's and it works "good enough". There are certainly better ways you could
set it up today, but they use what they have.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Attila Kinali
Sent: Monday, January 23, 2012 11:57 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Determination of the placement of the first pps
On Mon, 23 Jan 2012 08:43:01 -0800
Chris Albertson albertson.chris@gmail.com wrote:
It's a transit telescope (one that looks up at the local meridian) but
they don't use the sun. It looks at every start that passes in front
of it, thousands of them every night. Then they reduce the data by
knowing the exact location of every star and the time is pasted
directly overhead. This way they get thousands of measurements every
day. If you use the Sun you get only one per day.
Not to mention the solar noon varies by +/- 15min over the year
(don't ask me how this is called...old knowledge from my high school days)
A transit solar scope would be a fun Time Nut project. I think a
primitive one would be a photo cell and a length of wire. Measure the
time when the shadow of the wire sweeps across the cell. The trouble
is that with only one measurements per day it would time years to
build up uSec level data. Even if you placed the cell behind a pin
hold mask and used a fine piano wire, shades and baffles and so on.
Why not use a real telescope with a CCD and get more reliable data?
A friend of mine is into hobby astronomy and uses special type CCDs
for it (ie not even the hobbist look directly into the telescope anymore).
I guess it shouldn't be too hard to rig up some gear, a PC that collects
the pictures at precise instances and calculates the ephemeris time to
UTC/GPS difference. The only issue is that you'd need to put that telescope
somewhere with little light polution, otherwise you'll only get the
brightest
stars.
Attila Kinali
--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
The fundamental problem is our system of units is not defined rationally.
What is universal about a meter or a second or a kilogram? Nothing!
If you were suddenly transported elsewhere in the universe bareassed,
could you replicate the standards we use?
If you lived on another planet, perhaps Klingon, would the second make any
sense?
This problem was faced maybe 50 years ago by the SETI folks. How do you
know what frequency an ET might be transmitting on? 1.000000000 GHz? And
if their unit of time is different, what then?
The only purpose of a transite instrument is to determine the relationship
between two, essentially arbitrary, and essentially unrelated time scales.
YMMV,
-John
=======================
Hi
I think the key point is that they are still using a gizmo made in the
1800's and it works "good enough". There are certainly better ways you
could
set it up today, but they use what they have.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Attila Kinali
Sent: Monday, January 23, 2012 11:57 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Determination of the placement of the first pps
On Mon, 23 Jan 2012 08:43:01 -0800
Chris Albertson albertson.chris@gmail.com wrote:
It's a transit telescope (one that looks up at the local meridian) but
they don't use the sun. It looks at every start that passes in front
of it, thousands of them every night. Then they reduce the data by
knowing the exact location of every star and the time is pasted
directly overhead. This way they get thousands of measurements every
day. If you use the Sun you get only one per day.
Not to mention the solar noon varies by +/- 15min over the year
(don't ask me how this is called...old knowledge from my high school days)
A transit solar scope would be a fun Time Nut project. I think a
primitive one would be a photo cell and a length of wire. Measure the
time when the shadow of the wire sweeps across the cell. The trouble
is that with only one measurements per day it would time years to
build up uSec level data. Even if you placed the cell behind a pin
hold mask and used a fine piano wire, shades and baffles and so on.
Why not use a real telescope with a CCD and get more reliable data?
A friend of mine is into hobby astronomy and uses special type CCDs
for it (ie not even the hobbist look directly into the telescope anymore).
I guess it shouldn't be too hard to rig up some gear, a PC that collects
the pictures at precise instances and calculates the ephemeris time to
UTC/GPS difference. The only issue is that you'd need to put that
telescope
somewhere with little light polution, otherwise you'll only get the
brightest
stars.
Attila Kinali
--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Mon, Jan 23, 2012 at 8:56 AM, Attila Kinali attila@kinali.ch wrote:
On Mon, 23 Jan 2012 08:43:01 -0800
Chris Albertson albertson.chris@gmail.com wrote:
It's a transit telescope (one that looks up at the local meridian) but
they don't use the sun. It looks at every start that passes in front
of it, thousands of them every night. Then they reduce the data by
knowing the exact location of every star and the time is pasted
directly overhead. This way they get thousands of measurements every
day. If you use the Sun you get only one per day.
Not to mention the solar noon varies by +/- 15min over the year
(don't ask me how this is called...old knowledge from my high school days)
A transit solar scope would be a fun Time Nut project. I think a
primitive one would be a photo cell and a length of wire. Measure the
time when the shadow of the wire sweeps across the cell. The trouble
is that with only one measurements per day it would time years to
build up uSec level data. Even if you placed the cell behind a pin
hold mask and used a fine piano wire, shades and baffles and so on.
Why not use a real telescope with a CCD and get more reliable data?
A friend of mine is into hobby astronomy and uses special type CCDs
for it (ie not even the hobbist look directly into the telescope anymore).
I guess it shouldn't be too hard to rig up some gear, a PC that collects
the pictures at precise instances and calculates the ephemeris time to
UTC/GPS difference. The only issue is that you'd need to put that telescope
somewhere with little light polution, otherwise you'll only get the brightest
stars.
http://www.tass-survey.org/tass/dbms_access.html
I did this a while back. It is not as easy as it sounds. No it can
run from a house in the city. Even very small telescope will be able
to see hundreds of stars. But it is NOT as easy as you might thing.
first yu need to know exactly where the scope is pointed and and
which stars are recorded on your CCD and unless you work full time
this has to be automated. I was part of a group that did this. We
used lenses from 35mm film camera as "telescopes". We got a "group
buy" on a load of 135mm f/2.8 lenses.
Here is an example taken with a 135mm f/2.8 camera lens and custom
CCD. This si a "worst case" image taken from the city. Bright stars
are a problem because they saturate the CCD and and break the
centrioding algorithum. (we fit a 2D Gaussian "pint spead function"
the the image of each star and get near micro arc second resolution)
http://www.tass-survey.org/tass/dbms_access.html
The 'scope was aimed at a fixed point in the sky using a solid
non-tracking mount as these are by far the easiest to build. But
unless you track the sky the image of the stars move on the ccd and
blur. So we moved the CCD. Or I should say we moved the image
electronically by shifting the charge the match the moving image,
electronic image stabilization. It works and a dozen or more of
thee were run by the group. But when you get into the fine details
you see that atmospheric refraction (and other effects) is wavelength
dependent so now you need to measure color so you need multiple
cameras and calibrated color filters and the math involves matrix
solutions.
A wire and a photocell is something you could set up, and yes the
solar day is not constant because we orbit the sun in an elliptical
orbit.
Attila Kinali
--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Chris Albertson
Redondo Beach, California
On 1/23/12 9:45 AM, J. Forster wrote:
The fundamental problem is our system of units is not defined rationally.
What is universal about a meter or a second or a kilogram? Nothing!
If you were suddenly transported elsewhere in the universe bareassed,
could you replicate the standards we use?
If you lived on another planet, perhaps Klingon, would the second make any
sense?
This problem was faced maybe 50 years ago by the SETI folks. How do you
know what frequency an ET might be transmitting on? 1.000000000 GHz? And
if their unit of time is different, what then?
isn't that why they relate things to Hydrogen frequency, etc. (viz gold
plates on Voyager)
Yes. The 1421 MHz is about the closest, practical, universal standard
available to us at the moment. But is not absolute. What if you were in a
different gravitational field? (The Pound gravitational red-shift
experiment)
-John
=================
On 1/23/12 9:45 AM, J. Forster wrote:
The fundamental problem is our system of units is not defined
rationally.
What is universal about a meter or a second or a kilogram? Nothing!
If you were suddenly transported elsewhere in the universe bareassed,
could you replicate the standards we use?
If you lived on another planet, perhaps Klingon, would the second make
any
sense?
This problem was faced maybe 50 years ago by the SETI folks. How do you
know what frequency an ET might be transmitting on? 1.000000000 GHz? And
if their unit of time is different, what then?
isn't that why they relate things to Hydrogen frequency, etc. (viz gold
plates on Voyager)
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.