NGC 4945 behind the dust: 50 hours

[Placidus]

Last night we added another 6.5 hours of luminance to our previous (2016) mammoth run on NGC 4945. The seeing was a little better, and the final stack was a little sharper for it.

Big one here (https://photos.smugmug.com/Category/Astrophotography-at-Placidus/i-52Lq6dt/0/9bd53b1b/O/NGC%204945%20L%2018h30%20RGB%2011hr s%20each.jpg)

We previously showed the colour "as perceived", a drab orange-red, due to intervening Milky Way dust.

This time, (as others have done before) we tried for a more "colour agnostic" version, to show how it might seem if we had a slightly clearer view. The 11 hours per channel was enough to permit this.

Edit: "The colour agnostic" approach:

(1) Set the black point to the foothill of the histogram in each channel, so that the darkest parts of the image show as black, but with no loss of information.
(2) Select an area of special interest (in this case, the galaxy), and adjust the gain so that the galaxy is, on average, grey. That is to say, the red, the green, and the blue all cancel.
(3) Crank up the saturation, to show important differences, in this case, showing that some areas are very cool (now orange) and plausibly of great antiquity, some areas are very hot (now blue) and therefore very young.

Rather prettier, we think.

Despite the thick dust, one can just, just barely, make out a rather fine distant face-on spiral about half-way to top right, and three other galaxies far, far away.

Aspen GC16M and then FLI PL16803 on 20" PlaneWave. Luminance 18.5 hrs, RGB 11 hrs each.

Best,
MnT

[codemonkey]

That's a mammoth effort guys; respect! There's a cool little spiral at about 20% in from the left, and 60% down from the top. And what's that around the star in the bottom left, is it an irregular galaxy in the background?

[DavidTrap]

Magnificent!

DT

[Retrograde]

Amazing depth & lovely colours.
A gorgeous image.

[h0ughy]

Detail and colours are very satisfying. Awesome result

[Placidus]

Thanks Lee. It's pleasing to see any background galaxies at all in amongst the Milky Way stars and dust. Yes, it does look like a tiny baby NGC 55 hiding down there.





Thanks David!





Many thanks Pete. Hope we didn't overdo the colours, but there's an APOD where they went even further, so there's a precedent.





Thanks heaps David.


Best,
MnT

[lazjen]

Very nice. I had a bit of a scan around the image and I think I can see at least 6 other galaxies in there (plus at least 3 more that are strong maybes).

[Placidus]

Thanks Chris. Our highly experienced galaxy spotter (Mike after 3 coffees) looking at the TIFF on the 4K monitor found sixty three.

[multiweb]

:eyepop: So very smooth. Great field and colors. Love that little side-on hiding behind the star at 7 o'clock. Lots of interesting faint fuzzies in the field too. One for the poolroom. :thumbsup::thumbsup::thumbsup:

[Placidus]

Thanks Marc. Thrilled that you like it too.

[gregbradley]

Wow, 50 hours, that's a lot. I did some imaging of this one last night on a CDK17. Its a reasonably bright galaxy. I like the way you got rid of the yellowish colour gradient you normally see with this one. Very clever.

Greg.

[Placidus]

Thanks Greg! So often we go back to our archives and think, "Oh dear, we've come a long way since then", but this time, we were actually able to use, and add to, the data from yesteryear.

[strongmanmike]

An on going project, that keeps giving, of a very tempestuous galaxy, looks great :thumbsup:

Not sure if I have ever mentioned it..?..but when ever I see your images...all I can think of is your telescope :question: :evil2:

Mike

[Placidus]

Thanks Mike!


When travel is safe again, we'd love to have you and Angie to come and stay for a few days. It's not a bad drive up through Cowra and Canowindra.



Best,
MnT

[Ryderscope]

This is a great little field of galaxies MnT and you have presented us with a fine display.

[ChrisM]

Superb! Amazing clarity and depth.


Cheers, Chris

[topheart]

So much detail!!
Well done!!

Cheers,
Tim

[Bart]

Very smooth and loads of detail. Always looks like an untidy jumble galaxy.

[John K]

Holy cow! The detail in incredible.

Power of a 20" scope!

John K.

[marc4darkskies]

A huge effort delivering a compelling, smooth and detailed image M&T! :thumbsup:

But, but to be honest, I'm not sure about attempting to remove the effect of the intervening dust. How did you know how to calibrate out that effect? G2V calibration? Having said that a G2V star on the other side of the dust would almost certainly not be visible! In any case I'd actually prefer the warm orange and yellow tones imparted by the dust (cf my old 2009 rendition here (https://pbase.com/gailmarc/image/110479642/original)).

[Placidus]

Rodney, Chris, Tim, Bart, John, Thanks so much! We try to please.



That's a very fair comment Marcus. I used the "Colour Agnostic" approach, of setting the average colour of the galaxy to be grey, (that is to say the red, green, and blue contributions all balance on average), on the grounds that the human eye is interested in differences: we can see in sunlight, we can see by red candle-light, and our brains work out what is what. Secondly, if we set the average colour to be grey, we can crank up the saturation, not to show the "true" colours, which are pinkish whitish white, yet whiter white, and just sometimes vaguely bluish whitish very white, but so that we can see physically meaningful things: areas with old stars marked out as exaggeratedly warm oranges, areas with brilliant young OB stars as exaggeratedly blue, much in the same spirit as we mark grassland and forests on a map in green, lakes in blue, A-roads in yellow, and the British Commonwealth in red, even though it isn't. Narrowband is the perfect example: we're using colour to convey information. I hope that what we've done here is to show that there are plausibly areas of active star-formation with hot young blue in a galaxy that is normally shown as yellowish yellowish yellow. Fair enough to say, "you don't know that: you're just guessing, or assuming that the galaxy is normal; that's not science", but it is also fair to say, "If we assume that this galaxy is fit and healthy, this is where the new stars are, and this is where the old ones are".

As to precedent most sanctified and holy:

APOD by Martin Pugh
(https://apod.nasa.gov/apod/ap190822.html)

Once again, we don't do science by appealing to authority, but the colour DIFFERENCES, which is what I'm showing, do mean something real and solid. No finger painting was done. And anyone can copy the colour-agnostic method (which I mentioned in the original post, but have now fleshed out in detail there) of setting the black point so there is no average colour cast in the background, then setting the colour of the galaxy so that it is on average grey, and then cranking up the saturation. You could even do that to your image, and you should get much the same result. That is science.

(Apologies: I seem to be on a rant, which is naughty, but while I've got up a head of steam, what is a sin against the light is presenting a globular cluster so that it is on average blue. That is physically impossible, and conveys no information. It is also a sin against the light to prepare a narrowband image so that there is no green. An area of low ionization strong in H-alpha should be green. If it isn't then one is finger-painting, and not being true to the light.)


Sorry, that sounded exactly like the Monte Python sketch where I wouldn't become a Freemason if you got down on your knees and begged me. Moose bites can be very nasty. Normal transmission resumes immediately. The people who wrote this have been sacked. :scared3:

Best,
Mike

[Atmos]

Pretty darn good M&T, it's great that you've been able to use previous years data as well and just add more to it. It's one of the great things about everything being so far away, it doesn't move much year to year :lol:

I agree with you on globular clusters too! Disregarding blue stragglers, given their age they have a peak "blueness" of red as there shouldn't really be any stars larger than 0.8 solar masses.

[Placidus]

Thanks Colin! It was actually a source of some great pleasure to register the new luminance with the old, set them to the same zero and brightness, and flick between the two. Visually, nothing happened: they were the same. That is reassuring.



And thanks for the moral support regarding beautiful blue globulars.

[Andy01]

Yep, sharp & clear - big and bold - looks great, well done! :thumbsup:

[marc4darkskies]

Without accounting for the precise absorption characteristics of the intervening dust, that approach makes sense Mike and is of course a perfectly reasonable approach! I saw and appreciated the colour differences in your excellent image. I was only wondering how you were trying to render an invisible something.

Believe it or not, my approach is also quite agnostic. I seek to enhance what is "visible" as exposed via the raw RGB stacking done in CCDStack which is, arguably, an agnostic process. I often refer back to the raw RGB to make sure my PS processing to enhance colour isn't corrupting the actual colour content. The only thing I'd seek to rectify in my rendition of 4945 is the glaring fact that the halo should be an orange-brown colour. Don't know why I made it grey. My excuse is I was still relatively inexperienced. :doh:



:lol: No no - don't sack them, just give them a good talking to. :lol:

[alpal]

Hi Mike and Trish,
that is such a great image.
I look forward to seeing your work.


cheers
Allan

[Placidus]

Thanks Andy !!!!



All makes sense Marcus. Many thanks.



Thanks Allan, we are encouraged. Right now, it is exact new moon, and raining torrentially. Soon!

[PeterSEllis]

Hi Mike and Trish,

Well, it doesn't get much better than that. Whew, 50 hours, here in Melbourne it would take me about 5 years (if not longer) to get that sort of time on one object. I envy your site, "not to mention the equipment".

Peter

[Placidus]

Thanks Peter.

The "equipment" of course is a double-edged sword. It sure helps suck up the photons, and it's fairly forgiving of focus, but the wide aperture means it's at the mercy of the seeing, the long focal length means a small field of view, and it really shows up any errors in tracking. It seems that its real strength is in finding super-faint detail, like tiny background galaxies.