NGC 3579 - An Emission Nebula in Carina
I had originally set out to image NGC 3576, “The Statue of Liberty Nebula”, but mixed up the NGC numbers. Thankfully, these two emission nebulae are right beside each other. I ended up capturing my original target, but not without a few tense moments when I realised I had the wrong target.
Wikipedia says:
NGC 3576 is a bright emission nebula in the Sagittarius arm of the galaxy a few thousand light-years away from the Eta Carinae nebula. It is also approximately 100 light years across and 9000 light-years away from Earth. It was discovered by John Frederick William Herschel on 16 March 1834.
This nebula has received six different classification numbers. Currently, astronomers call the entire nebula NGC 3576. A popular nickname is “The Statue of Liberty Nebula” because of the distinctive shape in the middle of the nebula. The name was first suggested in 2009 by Dr. Steve Mazlin, a member of Star Shadows Remote Observatory (SSRO).
Within the nebula, episodes of star formation are thought to contribute to the complex and suggestive shapes. Powerful winds from the nebula’s embedded, young, massive stars shape the looping filaments.
For once, the new moon coincided with a weekend, so I was able to get away to the ASV’s dark sky site for two nights of astro imaging. It was also the ASV’s Deep Sky Section meeting up there, so there were other keen astronomers to talk with.
The Friday night was a waste of time - the skies where clear but the wind was gusting strongly. Of the 120 frames that I captured, I was able to only use 56 of them. The rest were rendered useless by telescope shake from the wind. My guiding has been sitting around 0.6 RMS, but the best I could do that night was about 2.5 RMS, with stretches of over 5 RMS.
I gave up around midnight and retired to get some much needed sleep.
Saturday was a typical summer day - clear and sunny. The temperature hovered around 36C, so perhaps a bit warm, yet not overly hot and uncomfortable. The fact it was a dry heat made it far more tolerable.
Saturday night was a much more productive night - my guiding sat at around 0.6 RMS all night (apart from the dense line of cloud that rolled through late in the night and took out a few of the sub-images) so I was happy with what looked like good data coming in from the camera.
Just for kicks, I put the cross-hair filter on the telescope to create the ‘X’ shaped diffraction spikes on the stars. I’m still undecided as to whether they look good or not in an image like this one. For stellar clusters, I think the spikes look great, but not-so-great otherwise.
Processing-wise, I had to wait until Thursday to capture the usual calibration frames and start work on getting an acceptable image.
Why did I have to wait? We had a very short, but very intense storm that knocked out power to a large area of the state. The power went down at 15:30 on Tuesday afternoon and wasn’t restored until just before 06:00 on Wednesday morning. Some parts of the state are still without power as I write this entry on Friday.
I used Sirilic to stack both sets of data into one image - the L-Enhance data for the additional H-Alpha colour, and the UV-IR Cut filter to get real star colours. The final output can be seen below in Image 1.
Image 2 is only the L-Enhance data, to show off the muted colour of the stars against the deeper red of the H-Alpha emissions.
Normally I would use starnet++ to split the stacked image into two sub-images - one with the ‘background’ nebula and one with only the stars. I’d process these images separately and then recombine them to get the best of both worlds.
Oddly, when I did this, the resulting image was dull and muted when compared to the processed single image. I suspect it was something I was doing in Affinity, although I can’t recall doing anything too different to my usual process. So these images got left “on the cutting room floor” as it were.
I had a look around for other images of this nebula and whilst there are some good images out there, I think a lot of them are over-processed and garish, looking like an explosion in a fluorescent paint factory. Yes, I know a lot of them are processed with the false-colour Hubble palette, but there’s no need to hyper-saturate the colours.
Update - 2024-02-24
I haven’t been happy with the previous images and had the idea to combine the background (nebulosity) from the L-Enhance data with the properly coloured stars from the UV-IR Cut data. So the third image in this series is just that.
I split out the stars from the UV-IR Cut image with starnet++ and then layered them over the L-Enhance data. To my eyes, it’s a better overall image because I was able to work on both layers separately. The actual processing was fairly simple - boosts to the brightness, contrast and exposure on both layers to compensate for the dimming caused by the layering, and then some small colour tweaks to the entire image to make it look good.
Whether I gather more data and try again is up in the air. I don’t seem to get much time to capture photons, and there are so many different targets out there to capture. We’ll see.
Data set 1:
- Gain: 100
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 120 seconds
- Frames: 103 Lights, 50 Darks, 50 each of Flats and DarkFlats (206 minutes integration in total)
- Filter: L-Enhance
Data set 2:
- Gain: 100
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 30 seconds
- Frames: 56 Lights, 50 Darks, 50 each of Flats and DarkFlats (23 minutes integration in total)
- Filter: UV-IR Cut
Processed with Sirilic and/or SiriL (stacking, pre-processing, basic stretching) before tweaking in Affinity Photo v2
Equipment: SW72ED@420mm / HEQ5-Pro / ASI183MC-Pro / SV165+SV305 / Kstars/Ekos
Image 1 - Both data sets
Image 2 - L-Enhance data only
