Shark Attack!

[Mike Lewis]

I went shark hunting, for a target that has been on my list for a while, but that I have not tried for until now. I was able to wait until the better portion of the moon cycle to go after this very faint object and I think that paid off. I initially took LRGB data, plus short RGB data for the stars (like I usually do) but ended up not using the luminance data or the short exposure RGB adata. I could not get an LRGB combo I liked more than the straight RGB, and the short exposure star data just did not look as good as the star data from the 900 second subs, so I just added that back in.

Including smaller dust nebulae such as Van den Bergh 149 & 150 (blue patches in this image), the Dark Shark Nebula, sometimes cataloged as LDN 1235, spans about 15 light years and lies about 650 light years away toward the constellation Cepheus. And it actually looks like a shark, too!

It is still amazing how little detail seemed to be in a single 900 sec subframe, compared to what I was able to pull out of the stacked and combined data. Thanks for looking, and any comments, questions or critiques are always most welcome.

Astrobin link here: https://app.astrobin.com/i/yd18m3

Equipment:
Poseidon-M Camera @ -5C and Gain:125 Offset:25
Astro-Physics Mach2 Mount
Williams Optics Cat 91 Refractor, 448mm @ f/4.9
Antlia Pro Filters (3nm narrowband plus RGB)
Askar FMA180 Guide scope with ASI290MM

Software:
Pixinsight Commercial Version 1.9
Lightroom CC
Photoshop CC
N.I.N.A. Control Software
BlurXTerminator (Russell Croman)
StarXTerminator (Russell Croman)
NoiseXTerminator (Russell Croman)
Astro-Physics APCC and APPM

Light Frames:
Gain 125 / Offset 25
Red: 24 x 900 secs (6 hours)
Green: 24 x 900 secs (6 hours)
Blue: 22 x 900 secs (5 hours 30 mins)

17 hrs 30 mins total

Dark Frames:
10 x 900 secs (2 hr 30 mins)

 

[JimFox]

Perfect in every way Mike! You really nailed this guy. It's so faint, and I know it can just look like a pile of noise even until it gets processed properly.

 

[Mike Lewis]

Perfect in every way Mike! You really nailed this guy. It's so faint, and I know it can just look like a pile of noise even until it gets processed properly.

Yes, even with 15 minute subs I originally thought I would not get anything good at all because the results were so faint.

ML

 

[Comet Hunter]

wow, nicely done

 

[Mike Lewis]

wow, nicely done

Thanks Ed! It turned out better than I was expecting from looking at the individual subs. It really is faint I guess.

ML

 

[JimFox]

Thanks Ed! It turned out better than I was expecting from looking at the individual subs. It really is faint I guess.

ML

I did a few 10 min subs last night with the Antlia Alp-T filter. But it was a bit windy when I was starting, and I was getting some star movement at 10 mins, so I switched over to the Helix neb where I could run 5 min subs instead.

I might try to process my hour of subs at 10 mins just to see if I can pull anything out. Hopefully I can get something, because when I took my test shots, I couldn't see anything but stars, so I wasn't even sure how the shark was located as it was framed in my rig. I went to Astrobin and looked yours up to see if I could turn on it's annotation where it will plate solve and show the object/stars names in the image so I could compare that to my Sky Atlas I use in ASIAir to know how it's being framed. But I couldn't remember how to turn on the Plate Solving. So I just took my shots blind if you will.

 

[Mike Lewis]

@JimFox

So sorry, perhaps too late to help you out now. But as I said originally, if you hover over the image in Astrobin it will show someww plate solved items in the frame. I also ran a more thorough plate solve inside of PixInsight and got this:

Looks like 3 reference stars, and then a couple of very small galaxies that will likely not help you much...I did include the location grid too, perhaps that is helpful if you can enter raw coordinates directly. Looks like RA 22hrs / DEC +73 degrees is about the center of the body of the shark...

ML

 

[JimFox]

Thanks Mike!

I was just using my phone to access Astrobin while I was outside my sons house, so I didn't see any way to mouse over. But thanks for the tip, next time I will just run into the house and use my laptop.

And yeah, it's too late now, nothing but clouds the next 2 nights. Though I am leaving my rig setup on his basketball court for now and going to take the chance to run a new set of darks on it, after the temp drops tonight. Might as well take advantage of that.

And you mentioned about reference stars in the image, the one thing that had jumped out to me the other day was there is that small galaxy PGC67671 in it, that I thought was kind of a cool little thing.

Are those Oiii areas from reflection nebula? I know you are using 3nm filters, but I am wondering if that blue was contained in your 3nm Oiii filter or from the RGB data you took? Because I am wondering if the Antlia ALP-T that I used which is 7nm and not recommended for reflection nebula would pick that blue up or would I lose it?

 

[Mike Lewis]

The blue comes through at this level from just the blue filter, although these were 15 minute subs so that helped. I did not take Oiii for this one so I cannot say for sure, but I think the blue in these areas is from light scattering (the same thing that makes our sky blue here) and not from Oiii excited emissions.

And yes, that little galaxy is cool and also a great indicator of the middle of the frame,. Not every astro program will have the PGC galaxy catalogue objects available though unfortunately. I am not sure if the ASI Air catalogues include these objects.

ML

 

[Andy Elliott]

That's very nice indeed.

 

[Mike Lewis]

That's very nice indeed.

Thanks Andy!

ML