NGC5128 - Galaxy in Centaurus (Centaurus A)

We finally got some clear skies here and I took advantage of a few scant hours of good viewing (before the humidity ramped up and mist rolled in) to grab more data of NGC5128 (aka Centaurus A).

You can read about my previous capture of the galaxy here - along with all the interesting information from Wikipedia.

For the first image here, I combined the data from my previous session with the new data to get a composite image. As with all astro work, more data makes for better images.

I was initially concerned about stacking the two sets of data because I used different camera setups. (The first set had no filters in place, whilst the second had the UV-IR Cut filter and hence a different camera rotation because of a different optical train.)

However, there’s a handy Python program called ‘SiriLic’ that creates custom SiriL scripts and allows for all manner of different image data sets. It’s a bit tricky to get up and running if you’re not using their pre-built packages and unfamiliar with the command-line interface.

Interestingly, scaling the image down appears to have given the blue-tinted stars a green tinge. If I get motivated I can go back and see where that oddity came from.

On top of that, my flat frames didn’t seem to work out quite right (what else is new??) so the dust-motes on the telescope lens weren’t removed fully. So I had to crop the image tightly to avoid them. I suspect that a good cleaning session of the lens will sort that out - as well as more experimentation with getting the flat frames better. We’ll see.

I had originally planned to get 4 hours worth of data but had to give up with only 3. The clear skies vanished into a hazy mist that rendered all but the brightest stars invisible. Of course, that totally screwed up the guiding and what images were captured were so over-exposed as to be totally useless. The joys of having a hobby that’s so dependant on the weather…

Both images clearly show the dark dust/gas lanes that bisect the galaxy, and the huge spread of stars from the central core.

Session 1 Image details:

  • Gain: 100
  • Offset: 10
  • Temperature: 0 degrees C
  • Exposure: 60 seconds
  • Lights: 60 (1 hour)
  • Darks: 50
  • Flats: 50
  • Dark Flats (Bias): 50

Session 2 Image details:

  • Gain: 100
  • Offset: 10
  • Temperature: 0 degrees C
  • Exposure: 120 seconds
  • Lights: 90 (3 hours)
  • Darks: 25
  • Flats: 25
  • Dark Flats (Bias): 25

Both sets of data were stacked using SiriLic, then pre-proc’d in SiriL, final processing in Affinity Photo

NGC 5128 - Siril

This second image uses only the data from the most recent session, so I didn’t need to worry about getting everything aligned correctly.

I also tried stacking it with SiriL, but the results weren’t great, so Affinity Photo got the nod for this one. (I was testing out AstroPixelProcessor but the trial license has expired and I haven’t gotten around to buying it yet. At a bit under AUD$300 it might be a while before I do take the plunge.)

Image details:

  • Gain: 100
  • Offset: 10
  • Temperature: 0 degrees C
  • Exposure: 120 seconds
  • Lights: 90 (3 hours)
  • Darks: 25
  • Flats: 25
  • Dark Flats (Bias): 25
  • Stacked and proc’d in Affinity Photo

NGC 5128 - Affinity Photo