ASTRO: Southeast portion of the Cygnus loop

The Cygnus loop consists of many separate NGC, IC and other
designations, some with common names as well. NGC 6995 is the portion
in this image with the start of IC 1340 at the bottom. The Cygnus loop
is about 3 degrees across. While sometimes called a super nova remnant
that isn't quite correct. It is caused by the shock wave of a super
nova that happened some 5,000 to 8000 years ago (old estimates say up to
100,000 years ago). It seems to get younger with every new study. The
distance is rather uncertain but a measurement by FUSE puts it about
1470 light-years away. If correct that means the 3 degree bubble is
over 76 light-years across. Obviously the debris of the super nova
couldn't be seen spread over this vast area. In fact no debris or other
sign of the super nova is to be seen other than the shockwave itself.
That is compressing interstellar gas ahead of it. The energy from the
shockwave causes it to glow with the Hydrogen showing as mostly red and
the OIII being rather blue (I'd have expected more cyan but it came out
blue for me so something else is also involved I'd think, H beta
probably). It's diameter of a bit over 76 light-years gives an average
speed of 1.5% the speed of light or about 2800 miles per second or 10
million miles per hour! You might expect that motion to be visible.
Remember the material isn't moving with the shock wave. It is just the
compressed gasses excited by the shockwave as it passes through them.
Instead new shock features will become visible as old ones are left
behind. That will take time though by comparing very old images some
features on the outside of the bubble might be expected to brighten and
hints of new ones develop as those toward the center dim and fade away.
Comparing an image I made (very poor) in 2006 to one made last year I
found no obvious change though the exposure times and acquisition
techniques were so different real brightness changes are hidden.

Note the distant faint, apparently dust reddened galaxies on the left
side of the image, especially toward the bottom. Oddly they aren't seen
on the right side in the middle of the loop though some are on the
western side of the loop. None had redshift data and many weren't
listed at all in NED which has only picked up those with strong 2 micron
emission to make the 2MASS catalog. The biggest and brightest (near an
orange star) isn't listed at all. Thus I didn't bother make an
annotated image.

I had hoped to work on a large mosaic of the east side of the bubble.
But thanks to the highly variable weather that didn't happen. I did get
lucky for a couple hours of far better than usual (for this year)
conditions which allowed me to capture this part of the eastern loop.
At this rate I should finish the mosaic by 2020! As usual this is a
pure LRGB image, no narrow band data was used and I only had good skies
for my usual short 40 minutes of luminance and 60 minutes of color data.
Far less what most would use for this object. Still it is one of my
best images for 2013.

I've included images at both 1" and 1.5" per pixel.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME
--
Prefix is correct. Domain is arvig dot net

Mighty image Rick.
The nebula is spectacular, although the small galaxies to the left of the
emission nebula are so unexpected to me that they almost drew more attention
than the main object.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
...

The Cygnus loop consists of many separate NGC, IC and other
designations, some with common names as well. NGC 6995 is the portion
in this image with the start of IC 1340 at the bottom. The Cygnus loop
is about 3 degrees across. While sometimes called a super nova remnant
that isn't quite correct. It is caused by the shock wave of a super
nova that happened some 5,000 to 8000 years ago (old estimates say up to
100,000 years ago). It seems to get younger with every new study. The
distance is rather uncertain but a measurement by FUSE puts it about
1470 light-years away. If correct that means the 3 degree bubble is
over 76 light-years across. Obviously the debris of the super nova
couldn't be seen spread over this vast area. In fact no debris or other
sign of the super nova is to be seen other than the shockwave itself.
That is compressing interstellar gas ahead of it. The energy from the
shockwave causes it to glow with the Hydrogen showing as mostly red and
the OIII being rather blue (I'd have expected more cyan but it came out
blue for me so something else is also involved I'd think, H beta
probably). It's diameter of a bit over 76 light-years gives an average
speed of 1.5% the speed of light or about 2800 miles per second or 10
million miles per hour! You might expect that motion to be visible.
Remember the material isn't moving with the shock wave. It is just the
compressed gasses excited by the shockwave as it passes through them.
Instead new shock features will become visible as old ones are left
behind. That will take time though by comparing very old images some
features on the outside of the bubble might be expected to brighten and
hints of new ones develop as those toward the center dim and fade away.
Comparing an image I made (very poor) in 2006 to one made last year I
found no obvious change though the exposure times and acquisition
techniques were so different real brightness changes are hidden.

Note the distant faint, apparently dust reddened galaxies on the left
side of the image, especially toward the bottom. Oddly they aren't seen
on the right side in the middle of the loop though some are on the
western side of the loop. None had redshift data and many weren't
listed at all in NED which has only picked up those with strong 2 micron
emission to make the 2MASS catalog. The biggest and brightest (near an
orange star) isn't listed at all. Thus I didn't bother make an
annotated image.

I had hoped to work on a large mosaic of the east side of the bubble.
But thanks to the highly variable weather that didn't happen. I did get
lucky for a couple hours of far better than usual (for this year)
conditions which allowed me to capture this part of the eastern loop.
At this rate I should finish the mosaic by 2020! As usual this is a
pure LRGB image, no narrow band data was used and I only had good skies
for my usual short 40 minutes of luminance and 60 minutes of color data.
Far less what most would use for this object. Still it is one of my
best images for 2013.

I've included images at both 1" and 1.5" per pixel.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME
--
Prefix is correct. Domain is arvig dot net