Questions about the moon

"Stuart Cooke" wrote in message
...
so would an optical array be able to see them then??

say i have 4 telescopes spread over, say, 1 kilometer, all with apertures
of
120mm, with the images slaved to a good pc with software capable of
integrating the images correctly, i would, theorectically, have a
telescope
with a extremely large aperture, right?
Yes, and no...
The problem is that you have to recombine the signal from the scopes, to
within fractions of the wavelength being imaged. This approach was first
done many years ago, with radio telescopes (relatively long wavelengths). In
recent times, it has been extended to first the infra-red, and more recently
the near infra-red section of the spectrum. Visible light now being used for
the first time, with scopes only a few tens of metres apart. You are looking
at needing to get the optical paths between the scopes, accurate to
distances in the order of perhaps 0.00005mm or better, even as the scopes
move across the sky. Even the ground itself, distorts by more than this,
from thermal/tidal shifting, over distances like 1km (hence the reason that
the scopes are kept closer together). Just combining the 'signal' (using CCD
sensors at each scope), does not give the resolution increase, to get this,
requires that the signal phase information is also combined, which is the
'hard part'...

Best Wishes

"David Knisely" wrote in message
.. .
Radio 893 wrote:

An why would it not be possible to see the flags even with the most
powerful
telescopes?

Because the flags are too small and too far away to be resolved by any
single
telescope currently in existance.

--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

"Stuart Cooke" wrote in message
...
so would an optical array be able to see them then??

say i have 4 telescopes spread over, say, 1 kilometer, all with apertures
of
120mm, with the images slaved to a good pc with software capable of
integrating the images correctly, i would, theorectically, have a
telescope
with a extremely large aperture, right?
Yes, and no...
The problem is that you have to recombine the signal from the scopes, to
within fractions of the wavelength being imaged. This approach was first
done many years ago, with radio telescopes (relatively long wavelengths). In
recent times, it has been extended to first the infra-red, and more recently
the near infra-red section of the spectrum. Visible light now being used for
the first time, with scopes only a few tens of metres apart. You are looking
at needing to get the optical paths between the scopes, accurate to
distances in the order of perhaps 0.00005mm or better, even as the scopes
move across the sky. Even the ground itself, distorts by more than this,
from thermal/tidal shifting, over distances like 1km (hence the reason that
the scopes are kept closer together). Just combining the 'signal' (using CCD
sensors at each scope), does not give the resolution increase, to get this,
requires that the signal phase information is also combined, which is the
'hard part'...

Best Wishes

"David Knisely" wrote in message
.. .
Radio 893 wrote:

An why would it not be possible to see the flags even with the most
powerful
telescopes?

Because the flags are too small and too far away to be resolved by any
single
telescope currently in existance.

--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

"Jonathan Silverlight" wrote in message
...
Right. But I think combining the images from four telescopes a kilometer
apart is still beyond our reach. Places like the Keck telescope in
Hawaii and the VLT in Chile are only using telescopes about 100 meters
apart, AFAIK. Even if they could, the moon probably doesn't have enough
contrast to make it work.
*SNIP*

I seem to remember doing an experiment when i was little with my dad, we
took 2 x 4 1/2" scopes and set them about 150ft apart, and he used some
technical equipment and used both images from the really old style video
cameras to create an image that showed a much higher light level, but how he
did it i cant remember, and, since hes died now its kind of difficult to get
the answer!!!

wish i knew how he did it coz it was cool!

"Jonathan Silverlight" wrote in message
...
Right. But I think combining the images from four telescopes a kilometer
apart is still beyond our reach. Places like the Keck telescope in
Hawaii and the VLT in Chile are only using telescopes about 100 meters
apart, AFAIK. Even if they could, the moon probably doesn't have enough
contrast to make it work.
*SNIP*

I seem to remember doing an experiment when i was little with my dad, we
took 2 x 4 1/2" scopes and set them about 150ft apart, and he used some
technical equipment and used both images from the really old style video
cameras to create an image that showed a much higher light level, but how he
did it i cant remember, and, since hes died now its kind of difficult to get
the answer!!!

wish i knew how he did it coz it was cool!