ASTRO: NGC 246 plus some galaxies

During my visit to country skies Abell 74 sunk too low for further imaging,
so I had to decide on an object for the remaining nearly two hours till
dawn.
NGC 246 came to my mind, which I can't reach from home. It was already past
meridian when I started the series, so it was between 25 and 20 degrees
altitude while I gathered exposures.
Fortunately it is quite bright. I did not do any narrow band images as I
wanted to include the countless galaxies that can be found in the left
(=northern) part of the image.

This patch of sky seems to be popular with satellites, as I only had a few
exposures I could not get rid of them by sigma stacking.

Taken from the village of Münchehofe with an 8" GSO RC at 1025mm focal
length on a G11 mount, Atik 383L+ camera, 3x10m for L and R, 2x10m for G and
B

http://ccd-astronomy.de/temp8/246gut.jpg

Stefan

Darned good for how low it is. Even on the meridian it is low for your
latitude. My early attempt at it is no better and it is higher in my
skies. If I ever get the seeing I'll try again.

Since I use only 2 to 4 subs much of the time I've developed a procedure
in Photoshop to remove satellites. Might work in other image processing
software. I know. I make a mean stack less one frame with a
satellite(s) for each that have a satellite. Say two of the four have a
satellite, that would be 4 stacks, one of all four and two without one
or more satellites. I then put the all sub stack on the bottom and
layer one of the images without a satellite over it. I use the marquee
tool to select the trails not in the upper image. I then select the
upper layer, invert the selection and delete (control-X). If the
background isn't quite the same the satelliteless layer it may need a
bit of curves adjustment to blend to the background layer. I find
pulling the center of the curve up or down better than using levels. I
forgot to mention gradients have already been removed before starting
this process. Just repeat for each stack. Where they cross a blip will
remain that is then cloned out. Not as quick and easy as a sigma reject
approach but leaves in the asteroids.

I know you don't use Photoshop but might work with something you do have.

Also I've found that the Poison mean rejection stack in CCDStack can
remove trails with only 3 frames to work with. It takes a bit of
fussing with parameters but can work wonders with so few frames to work
with, especially if the trail is not down in the noise level. Not a
free tool but one I've found better than anything else I've tried for
stacking and noise elimination in tough cases. Might not do so well
under your city LP. Never tried it under such situations. Also great
for color balance using data provided by eXcalibrator 4.2 (far easier to
use than earlier versions as it simply click and run) when SDSS data is
available. bf-astro.com/eXcalibrator/excalibrator.htm
bf-astro.com/excalibrator/OSCeXcalibrator.pdf
Second link is how to use it with CCDStack. The values it returns are
usable in other programs as well.

Rick

On 10/8/2013 2:01 PM, Stefan Lilge wrote:
During my visit to country skies Abell 74 sunk too low for further
imaging, so I had to decide on an object for the remaining nearly two
hours till dawn.
NGC 246 came to my mind, which I can't reach from home. It was already
past meridian when I started the series, so it was between 25 and 20
degrees altitude while I gathered exposures.
Fortunately it is quite bright. I did not do any narrow band images as I
wanted to include the countless galaxies that can be found in the left
(=northern) part of the image.

This patch of sky seems to be popular with satellites, as I only had a
few exposures I could not get rid of them by sigma stacking.

Taken from the village of Münchehofe with an 8" GSO RC at 1025mm focal
length on a G11 mount, Atik 383L+ camera, 3x10m for L and R, 2x10m for G
and B

http://ccd-astronomy.de/temp8/246gut.jpg

Stefan


--
Prefix is correct. Domain is arvig dot net

Rick,

thanks for the hints to remove satellites. AstroArt only allows rectangular
selections, so selecting only a satellite trail is not possible.
I sometimes help myself by using the "difference" function on two aligned
pictures, which produces a picture with a satellite trail and some noise
(plus some remains of stars), which can be subtracted from the marred image.
Actually sigma stacking works quite well in AstroArt5 with three pictures,
at least good enough to remove cosmics. Bright satellites are tougher to
remove.
In this case I guess I'll leave it as it is, with satellites, a PN and
galaxies I am covering quite a large range of distances ;-)

Stefan


"Rick Johnson" schrieb im Newsbeitrag
. com...

Darned good for how low it is. Even on the meridian it is low for your
latitude. My early attempt at it is no better and it is higher in my
skies. If I ever get the seeing I'll try again.

Since I use only 2 to 4 subs much of the time I've developed a procedure
in Photoshop to remove satellites. Might work in other image processing
software. I know. I make a mean stack less one frame with a
satellite(s) for each that have a satellite. Say two of the four have a
satellite, that would be 4 stacks, one of all four and two without one
or more satellites. I then put the all sub stack on the bottom and
layer one of the images without a satellite over it. I use the marquee
tool to select the trails not in the upper image. I then select the
upper layer, invert the selection and delete (control-X). If the
background isn't quite the same the satelliteless layer it may need a
bit of curves adjustment to blend to the background layer. I find
pulling the center of the curve up or down better than using levels. I
forgot to mention gradients have already been removed before starting
this process. Just repeat for each stack. Where they cross a blip will
remain that is then cloned out. Not as quick and easy as a sigma reject
approach but leaves in the asteroids.

I know you don't use Photoshop but might work with something you do have.

Also I've found that the Poison mean rejection stack in CCDStack can
remove trails with only 3 frames to work with. It takes a bit of
fussing with parameters but can work wonders with so few frames to work
with, especially if the trail is not down in the noise level. Not a
free tool but one I've found better than anything else I've tried for
stacking and noise elimination in tough cases. Might not do so well
under your city LP. Never tried it under such situations. Also great
for color balance using data provided by eXcalibrator 4.2 (far easier to
use than earlier versions as it simply click and run) when SDSS data is
available. bf-astro.com/eXcalibrator/excalibrator.htm
bf-astro.com/excalibrator/OSCeXcalibrator.pdf
Second link is how to use it with CCDStack. The values it returns are
usable in other programs as well.

Rick

On 10/8/2013 2:01 PM, Stefan Lilge wrote:
During my visit to country skies Abell 74 sunk too low for further
imaging, so I had to decide on an object for the remaining nearly two
hours till dawn.
NGC 246 came to my mind, which I can't reach from home. It was already
past meridian when I started the series, so it was between 25 and 20
degrees altitude while I gathered exposures.
Fortunately it is quite bright. I did not do any narrow band images as I
wanted to include the countless galaxies that can be found in the left
(=northern) part of the image.

This patch of sky seems to be popular with satellites, as I only had a
few exposures I could not get rid of them by sigma stacking.

Taken from the village of Münchehofe with an 8" GSO RC at 1025mm focal
length on a G11 mount, Atik 383L+ camera, 3x10m for L and R, 2x10m for G
and B

http://ccd-astronomy.de/temp8/246gut.jpg

Stefan


--
Prefix is correct. Domain is arvig dot net