I don't think we could call it "amateur/semi-pro" but the millisecond
pulsar J0437-4715 would be perfect for this. Bright and precise.

Only for southern hemisphere people though.

:-)

Jim Palfreyman

On 30 December 2016 at 19:59, Anders Wallin anders.e.e.wallin@gmail.com
wrote:

On Fri, 30 Dec 2016 10:59:03 +0200
Anders Wallin anders.e.e.wallin@gmail.com wrote:

I don't know of any such experiment already performed, but I am not up
to date on what's going on in the hobby astronomy community.

I am not sure whether sub-milisecond resolution is feasible, but
I think the "easiest" method would be to do a "modern" version of
an meridian telescope:

Using a camera fix mounted (ie not moving and if possible vibration isolated)
on a pedestal pointed at the sky, approximately looking south. A simple
webcam would be probably enough for first experiments, as long as you get
a good picture of the stars. A good compact camera which allows to use
a remote shutter with a proper lens and exposure control should be better.
Probably the best resource here are the people/websites that deal with
book scanning, as they tend to automate the whole picture taking process.
Using magic lantern (http://magiclantern.fm) with Canon cameras might
give additional features needed for the task.

circles onto the bright pixels) and figure out which star is which (using
astronomical list of stars). For this step there is a plethora of open source
astronomical software available, but I don't know how well they fit the task
of figuring out what the position of the stars relative to the camera reference
frame. After that, it's just some simple math of calculating the difference
between the position of the stars and where you would have expecteded them
at the time when the picture has been taken.

Some usefull software projects are:
http://astro.corlan.net/gcx/
http://www.clearskyinstitute.com/xephem/
http://starlink.eao.hawaii.edu/starlink
http://astro.corlan.net/avsomat/index.html
http://rhodesmill.org/pyephem/

HTH

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson

Another solution from ground can be radio observation using a precise
interferometer: radio wavelengths are transparent to the earth
atmosphere and there are various references like sun during day, and (if
antennas are sensible) bright pulsars and other radio sources during night.

Best Regards,

Ilia.

On 12/30/16 10:42, Attila Kinali wrote:

--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999

Attila
Lookup "Stellar compass" as used for determining space probe attitude.Can also be used to determine the direction of the centre of an image of a field of bright stars.Subarcsecond accuracy is fairly routine.Pattern recognition techniques combined with measures of the relative brightness of the stars is used to identify them.Subpixel accuracy in determining the location of the stellar image centroids is also routine. 
There is at least one US PhD thesis on such stellar compass techniques.A stellar compass technique has been used to determine the pointing direction of small portable telescopes without requiring precision axis encoders etc.
Bruce

On Friday, 30 December 2016 11:43 PM, Attila Kinali <attila@kinali.ch> wrote:

On Fri, 30 Dec 2016 10:59:03 +0200
Anders Wallin anders.e.e.wallin@gmail.com wrote:

I don't know of any such experiment already performed, but I am not up
to date on what's going on in the hobby astronomy community.

I am not sure whether sub-milisecond resolution is feasible, but
I think the "easiest" method would be to do a "modern" version of
an meridian telescope:

Using a camera fix mounted (ie not moving and if possible vibration isolated)
on a pedestal pointed at the sky, approximately looking south. A simple
webcam would be probably enough for first experiments, as long as you get
a good picture of the stars. A good compact camera which allows to use
a remote shutter with a proper lens and exposure control should be better.
Probably the best resource here are the people/websites that deal with
book scanning, as they tend to automate the whole picture taking process.
Using magic lantern (http://magiclantern.fm) with Canon cameras might
give additional features needed for the task.

circles onto the bright pixels) and figure out which star is which (using
astronomical list of stars). For this step there is a plethora of open source
astronomical software available, but I don't know how well they fit the task
of figuring out what the position of the stars relative to the camera reference
frame. After that, it's just some simple math of calculating the difference
between the position of the stars and where you would have expecteded them
at the time when the picture has been taken.

Some usefull software projects are:
http://astro.corlan.net/gcx/
http://www.clearskyinstitute.com/xephem/
http://starlink.eao.hawaii.edu/starlink
http://astro.corlan.net/avsomat/index.html
http://rhodesmill.org/pyephem/

HTH

            Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
                -- Miss Matheson, The Diamond Age, Neil Stephenson

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.

Bruce,

I think that you refer on prjects like Astrometry plate solving. I think
one should got a reference to get a time reference instead of scope
"pointing" reference, so, once one's got local coordinates in encoder
positions, for example the values of the north pole with an alt/az
mounting, can use a sub/arcsec plate solver to obtain good sidereal
timing reference. using two encoders helps much.

The problem can be visibility of the reference points, however.

Best Regards,

Ilia.

On 12/30/16 10:59, Bruce Griffiths wrote:

--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999

Hi Anders:

That's something I've thought about for decades using an optical system.  A few  years ago I looked at it again and
found that astronomical "seeing" limits the accuracy.  So the accuracy achieved by a spaceborne "Stellar compass" will
be much better than a ground based observation.  A radio based observation might work since the atmosphere would not be
a factor.
http://www.prc68.com/I/StellarTime.shtml

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

-------- Original Message --------

Brooke,

The problem in radio ground observation can be resolution accuracy, but
there's also a good transmission into far infrared wavelengths, which
could require smaller dishes to get stellar images. The problem of far
IR is the cost of right filters/sensor, which are a bit difficult to find.

Radio objects, on the other hand, can be solved using an interferometer:
LOFAR interferometers work at frequencies higher than 10MHz, frequencies
totally transparent to the atmosphere and easily computable even by
consumer PCs. There is some work done with common PCs using two RTL-SDR
dongles and two satellite dishes.

see http://www.sbrac.org/files/DTP_RX.pdf

Best Regards,

Ilia.

On 12/30/16 17:18, Brooke Clarke wrote:

--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999

On 12/30/16 9:53 AM, Ilia Platone wrote:

the earth's ionosphere is hardly perfectly transparent at frequencies
below, say, 10 GHz.  The effect is small at GPS L-band frequencies
around 1.5 GHz, but still large enough that you need to either make
measurements at two frequencies (so you can calculate the effect) or use
other data, if you want accurate "sub-meter precision" data.

At HF, the effect is huge: during daytime, you might not even be able to
see the signals you're looking for, either from D-layer absorbption or
F-layer reflection/refraction.

The real challenge at HF (e.g. LOFAR) is that it's not just a time of
flight thing, because the propagation is not in a straight line: the
anisotropic ionosphere bends the rays: and even better, the bend depends
on the polarization.  For GPS, the signal is CP, and the effect is
small, so they typically look at it as an overall propagation speed
effect. At HF, the effect is so large that's not really valid.

The ionosphere is also only stable on a time scale of <1 second: that
is, on a HF skywave path (and by inference, on a HF "through ionosphere"
path), signals are pretty much decorrelated at time scales greater than
3 seconds as clumps of ionization move around.  This is the fundamental
accuracy limit on things like the ARRL Frequency Measuring Test (FMT).

It's true that you can do the interferometry easily on a PC, but taking
out the ionosphere effect is tough, unless you carefully choose
observing time and avoid high solar activity events, etc.

I suppose one can do some sort of inversion process on measured data
from known sources at multiple frequencies to infer the ionospheric
structure, but this is a hard problem.

If you want to use RF interferometry, I'd go higher:  maybe Ku-band-
cheap electronics and dishes available.  There's some water vapor
attenuation, and I'm sure that changes the propagation speed a bit too,
but it's measureable with radiometry, you can easily tell whether there
are clouds in the path with a pretty simple Ku-band radiometer.  You'd
want to throw out days when there's rain.

I don't know if there's any useful celestial sources at Ku-band.  DSN
uses bright quasars as pointing & timing reference when doing Delta
Doppler One way Ranging (Delta DOR) but on the other hand, they're also
using cryogenic receivers with 34 meter apertures- something not
available to the casual (or even dedicated) amateur.

Hi:

Maybe this could be done with GPS or higher frequencies so the angular resolution would be better?

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

-------- Original Message --------