NGC 6058

The planetary nebula NGC 6058 in Hercules was discovered by William
Herschel on March 18, 1787. At 13th magnitude it isn't an easy object
visually in my 10" scope. It does appear rather green to me in my 10"
scope so I was surprised to find it quite blue in my data. While most
internet images of it show it as blue a few are indeed green. Why the
discrepancy I don't know. The only distance estimate I found put it at
about 11,500 light-years away. One paper puts its age at 5 to 6
thousand years. At 40" in diameter it would be about 2.2 light-years
across. That seems large for the given age. It may be quite a bit
older to have reached that size. That paper says it is made up of 4
separate oval shells all centered on the central star. It's been a busy
5 to 6 thousand years for this planetary.
http://www.astroscu.unam.mx/rmaa/RMx...0_pguillen.pdf

Being in Hercules there are a lot of background galaxies though most had
no distance data in NED. All that did are shown in the annotated image.

Due to the brightness of the central star I had to use 5 minute subs for
the luminance frames. By taking 10 of them I get somewhat the same
depth as 4 10 minute frames (12 is better but not enough darkness for
that in late June) due to the rather high read noise of my camera. This
posed a problem when I went to process this data many months later. I
found I had no 5 minute darks taken at the -20C temperature. In fact I
had no darks at -20C for any exposure, so scaling was out as I've had
good success scaling down as to time but never as to temperature. I had
to make do with new darks taken many months later. Not a great match as
the camera has aged over those months but better than nothing.
Fortunately the color frames were taken a different night and I
correctly set it for -25C for which I did have good darks. How I messed
up and used -20C for the luminance I can't fathom. Fortunately this was
taken June 26. I only had dark skies for the luminance images because
of my very short nights up here. The following nights I set the
camera's temperature correctly.

14" LX200R @ f/10, L=10x5' RGB=2x10', STL-11000XM, Paramount ME

Rick
--
Prefix is correct. Domain is arvig dot net

Rick Johnson wrote in news:51571fbd$0$19552$862e30e2
@ngroups.net:

It does appear rather green to me in my 10" scope so I was
surprised to find it quite blue in my data. While most
internet images of it show it as blue a few are indeed green.
Why the discrepancy I don't know.

Scotopic vision? And some folks trying to match the image data
to their perceived visual appearance?

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?

Rick,

that's a cute one.
I'll have to check if I have imaged it, but I don't think I have.

Stefan


"Rick Johnson" schrieb im Newsbeitrag
...

The planetary nebula NGC 6058 in Hercules was discovered by William
Herschel on March 18, 1787. At 13th magnitude it isn't an easy object
visually in my 10" scope. It does appear rather green to me in my 10"
scope so I was surprised to find it quite blue in my data. While most
internet images of it show it as blue a few are indeed green. Why the
discrepancy I don't know. The only distance estimate I found put it at
about 11,500 light-years away. One paper puts its age at 5 to 6
thousand years. At 40" in diameter it would be about 2.2 light-years
across. That seems large for the given age. It may be quite a bit
older to have reached that size. That paper says it is made up of 4
separate oval shells all centered on the central star. It's been a busy
5 to 6 thousand years for this planetary.
http://www.astroscu.unam.mx/rmaa/RMx...0_pguillen.pdf

Being in Hercules there are a lot of background galaxies though most had
no distance data in NED. All that did are shown in the annotated image.

Due to the brightness of the central star I had to use 5 minute subs for
the luminance frames. By taking 10 of them I get somewhat the same
depth as 4 10 minute frames (12 is better but not enough darkness for
that in late June) due to the rather high read noise of my camera. This
posed a problem when I went to process this data many months later. I
found I had no 5 minute darks taken at the -20C temperature. In fact I
had no darks at -20C for any exposure, so scaling was out as I've had
good success scaling down as to time but never as to temperature. I had
to make do with new darks taken many months later. Not a great match as
the camera has aged over those months but better than nothing.
Fortunately the color frames were taken a different night and I
correctly set it for -25C for which I did have good darks. How I messed
up and used -20C for the luminance I can't fathom. Fortunately this was
taken June 26. I only had dark skies for the luminance images because
of my very short nights up here. The following nights I set the
camera's temperature correctly.

14" LX200R @ f/10, L=10x5' RGB=2x10', STL-11000XM, Paramount ME

Rick
--
Prefix is correct. Domain is arvig dot net