This information, from an email, explains atmospheric 'airglow' and
problems it causes to astronomers trying to photograph from the ground
through the atmosphere.
-------Original Message-------
From: nt@newtimesenergy.com
Date: Friday, September 05, 2003 12:46:47 PM
To: greydie@look.com
Subject: FWD: Elfrad-Group All Clear on the Gravity Wave front
This person (email at bottom)is talking about the gravity waves on your
wepage http://cosmicastronomy.com/ to which I came across, and used as
a refferance to long gravity waves. He answers your question as to why
NASA and others can't find your waves in their pictures, because they
manipulate them out. The post showes up here.
http://aurora.myhostdns.com/pipermail/elfrad-group_elfrad.org/2003-September.txt
and you can join the group here to make a coment as I hope you do.
http://216.67.236.74/mailman/listinfo/elfrad-group_elfrad.org
PS. your site is ausome, thanks for the great work. It has helped me to
understand what gravity waves are, and how to harness them. Hopefully ,
coming soon. I am being blocked from the group now, so I can't make a
coment. All the best Thomas
----------Original Message ----------------------------------
From: Rich Oliver
Reply-To: Rich.Oliver@lowell.edu, ULF ELF Propagation
Date: Thu, 04 Sep 2003 08:09:27 -0700
I took a look at the link Thomas supplied as the basis for the warning
of a gravity wave tsunami. It was immediately obvious that the odd lines
in the image of a galaxy are an image artifact that crept in during the
"flat fielding" process. Ground based deep-sky astrophotography with CCD
cameras is a very challenging endeavor with many pitfalls.
One of the biggest is the airglow, which is like a permanent, diffuse
aurora. It is much too faint to be seen with the eye but it can be as
much as 50 times brighter than the faintest things we photograph. It is
ne cessary to expose a "flat field" image and subtract that from the
data images to get rid of it (and other factors that cause defects in
the image). The airglow is constantly changing and it is very tricky to
get this just right.
Sometimes it is not possible to take a flat field
near the time of the data image and an old or averaged flat field must
be used instead. The result is that we often wind up with images that
are not perfectly corrected for flat field. Since the airglow consists
of emission lines and the light must pass through the nonuniformly
thinned substrate of the CCD, the usual result is a pattern of fringes
superimposed on the image. Depending on the purpose of the images this
may or may not be a problem for the researcher, so an image might be
useful even with this defect. Anybody who does deep sky CCD photography
will immediately recognize the fringes for what they are and ignore them.
To be fair, the author of the site makes it clear that he is just
compiling images with fu nny things he can't explain, and that he knows
some of it must be image artifacts he doesn't understand. When he comes
to the "gravity wave" image he suggests that it looks like huge waves
rippling through the galaxy. He was right the first time - it is an
image artifact. My advice - don't worry about a gravity wave doing
us in.
Cheers,
Rich