Re: ATM Seeing

[Bruce Swayze <swayze@europa.com>]

At 08:21 PM 7/28/97 -0400, you wrote:
>
>There is one thing that I wanted to query the group on... I
>live in South Carolina and HERE it is considered very very difficult to
>see the central star in the ring. I have only seen it with my 30" and
>then not always. I have friends that have been doing astronomy for years
>and years here and they have never seen it. Are the seeing conditions
>THAT BAD HERE?????!!!!!

Gary,
The answer to this question isn't a quick and easy one.  The ability to see
the central star in the ring, from my experience, depends on a number of
factors all lumped together in what we call "seeing".  I've never been to
your state, and I don't know how good (or bad) the seeing is there, but I
have seen the central star in my 15-inch.  It was also seen that night by
an experienced observer friend who was there at the time and verified the
sighting.  He sees it regularly in his 20-inch.  I'm sure somebody will
report seeing it in even a smaller scope.  On the other hand, there have
been nights when we couldn't see it in the 40-inch.  We get some nights
here in Oregon with extremely sharp seeing conditions allowing
sub-arcsecond resolution, though not very often.  One night last fall, the
seeing was so good that we were actually able to put a barlow in a barlow
along with a high-power eyepiece and observe Saturn at about 2,100 power in
the 15-inch.  This was verified by a group of about 10 other observers, as
we all stood around with our mouths open.  That was a first!  

The key factor, imho, is to obtain the best CONTRAST.  I should add that it
takes exceptionally good optics and critical attention to collimation.  I
have had the best results on the ring nebula using the highest allowable
magnification.  Also, use a high quality eyepiece that gives you excellent
contrast and pinpoint images (I like my Naglers).  I'll center the nebula
in the field of view and then just stare around the perimeter of the field,
allowing the center of the ring to be seen by averted vision.  If it's a
good night and I'm lucky, I'll see the star pop into view during brief
moments of sharp seeing.  

We had a lively discussion in our club a while back about the word
"seeing".  Those who were looking for something more accurate and
quantifiable like to break it down into the "transparency" of the sky, and
another description of the "steadiness" of the atmosphere.  You can have
nights with very good transparency, showing inky black skies and high
contrast, but horrible turbulence and big fuzzy blobs for stars.  On the
other hand, we sometimes get nights with poor transparency, or even a very
thin fog and washed out skies, but the air is so steady that views of the
moon and planets knock your socks off.  (You know it's good when Jupiter's
moons resolve into sharp little disks.)  These two factors run the spectrum
from one end to the other, and once in maybe 3 or 5 years you get a night
like the one I described last fall when it all comes together.  

Bruce Swayze