Nice reply Dan,

The real issue is why are we building ground based scopes at all!

Quite frankly any ground based scope is an AMATEUR scope

Build a Shubble

or a Hubble Bubble

or just plain something that hasn't been thunk up yet
why hasn't it been thunk up yet?
because we need to build ontologies that allow us to grasp new concepts,
to do so requires new experiences (not remote ones) and time in space

so the next real Hubble (the one that answers as many questions as the old
one)
should be in space and parked near the ISS
(or better yet A REAL SPACE STATION - a Von Braun Wheel...)

that way the astronauts can do what they are named for (astronomy)
instead of "make work" so that the military-industrial complex can be kept
in war fighting shape.



"Dan Mckenna" wrote in message
...


Yes, when one puts in the hard work in a site survey and sees that the
results are mostly not taken into account then its clear how the final
decisions could be viewed as "political".



right then

1) why do you think that the periods that you quoted site testing is
performed for are adequate to provide a real baseline of seeing/weather?
117 days??? why is this adequate????? no really, WHY?????

Site testing is an evolving science and the results obtained are usually
forgotten and not followed up on. In general one wants to have
simultaneous measurements from all sites considered and not the usual one
set up that is moved. The sampling should be based on wind conditions as
it drives and is related to the lower levels where the seeing contribution
is the greatest. One can, by knowing the climate wind rose for a site get
a good guess on how well the site testing sampled the wind directions and
thus the "astro climate".

A very good case in point is the site survey for CFHT on Mauna Kea. They
did a good job measuring the thermal high frequency structure from a
multilevel tower and did not catch all the effects due to length of time
the project ran. The data showed the important low level structure like
atmospheric gravity waves and the turbulence as a function of wind
direction but there was no in depth follow up.

The bottom line was that they believed that the seeing was no better than
1 arc second and the mirror was not figured as well as could of been.

As we know the seeing gets better than 0.5" on Mauna Kea and we saw times
when the image quality reached 0.28" and was steady meaning the telescope
was not atmosphere limited.

Other site surveys have been disregarded because the contractors said
there would be a problem building there.

Older site surveys used near to the ground "polaris telescopes" that
were mostly contaminated by the ground layer.

On Mauna kea you can get 1" from the first 20 meters of air.

The other challenge is usually there is a lack of strong influence on the
atmospheric side when it comes to something most astronomers do not
directly study. It took decades be for the role of atmospheric gravity
waves was accepted.

Another issue is that the telescope structure, enclosure design and
construction have a strong influence and can confuse the results of the
site survey as contrasted to the delivered image quality.

Most efforts now are to the titanic telescopes that will have their glory
in the infrared and so water vapor is more important than seeing.

Some think that you need a multi level multi color multi beam adaptive
optics and you can correct the seeing.

I feel that above all you start with good seeing and work to preserve it.

To measure seeing one needs at least a 1 meter telescope and a well tuned
SCIDAR. This is expensive and is usually done after the fact.

One also needs atmospheric scientist and not astronomers attempting to
play a trained and well seasoned meteorologist. Recent advances in high
resolution atmospheric models and remote sensing such as FMCW radar and
LIDAR are not being integrated by the observatory builders in site
selection.

Oh well, it's only a Hobby and the seeing is what it will be.

Dan (been there done that)