Color in DSO objects

[Dragan]

Hi everyone,

As i was typing up this weeks OOTW, I got to thinking about other objects in which color can be observed in. I wanted to start a thread where everyone can chime in with their personal experiences as to where they see color. For example;

As the OOTW stated, I tend to see pink/red in the outer circumference of IC 418 in various instruments above 16". The pink contrasts nicely with a white core.

NGC7662 the Blue Snowball lives up to its namesake and shows a definite aqua or turquoise hue in my 25".

Tho I'll add more, these are just two examples of mine to help kick this off. I thought it would be cool to start a thread which, if this works out, could turn into a neat little database of objects.

[Marko]

I don't see color often other than in certain famous stars or very bright PNs. Certainly giant scopes (> 30") have made color more obvious to me than in my 18". One of the most stunning color objects seen in a 33" was the Ghost of Jupiter, Ngc3242. Have seen color in that 33" a few times on targets my 18" will not show color. Have seen in a 12" distinct yellow in the deep south homunculus nebula that surrounds the odd star, Eta Carinae. Certain bright reflection nebulae have appeared blue to me for some objects, M45 included if at a dark site.

Generally I seem to need to see a 'white' star of fair magnitude in the edge of the field with black field then the nebula for me to be able to claim color if at all. If the whole field is a dim glow I generally don't see the color unless it is a very bright object.

It has been a goal of mine to try to detect color better and I am hoping my new 13mm Ethos known for contrast will help me see the color of the 'green' or 'blue' objects easier than my other eyepieces.

[Dragan]

Hi Mark,

There are going to be many many variables to this thread but I thought it would be interesting to bring those variables to light. Object type/brightness, primary aperture, sky conditions and age/experience of the observer will just be a few. I hope to start a discussion which would lead to an interesting list of objects we can refer to when looking for color in the EP.

Your mention of needing a white star in the field to help improve any color is interesting. I wonder if that is why I see such dramatic color in IC418?

[Vic]

Hi all!
I was very surprised recently (16 Oct) when I was observing NGC 6572. The conditions were not very good (SQM-L only 20.59, high humidity, bad seeing), the planetary nebula was already quite low, but the color was extremely green.
I have observed this little beauty many times. Usually it has only light green tint in my 16" dobsonian. But in this case it was completely different. I used low magnification (135×) and I was shocked!
Now I understand why it has the name "Emerald nebula".

I also remember seeing red color in M42 in 42", but it was not very prominent.
Vic

PS: I'll also try the Spirograph nebula again. But unfortunately it is always low here at 50N (Central Europe). I haven't noticed any colors there so far.

[Marko]

Hi Dragan,
Thanks for clarification of all objects including stars, I was not entirely sure of you intent after the discussion of spirograph nebula. Over the last few years it has been enjoyable to look for many colorful pairs or even unique colored solo stars (Hinds Crimson star) and so on.

Another trick of the white star is to have no filter and look at the spread out defocused star then go back into focus to see the PN slightly teal nebula color of OIII but here again I only tend to see any teal in the brighter PNs this way.

I don't think I can claim red tint except in red stars. I should try for that. I have been very curious in just how much red from H-Alpha can even be detected (as grey of course) and have experimented with non-standard filter stacking but that has not yielded much results and is a different thread here on DSR I called 'filters for fun science' in the equipment forum.

[shneor]

I, too, have seen the very distinct yellow "egg" surrounding Eta Carinae, with a 13.1" f/5 I took to New Zealand in 2000 using a 20mm Nagler Type 1. But let's not forget the pink, green and blue of M42, usually in my 22" f/4, but also recently in a 14" cat at TAAA's CAC site in southern Arizona.

[Marko]

Ok, the 'gauntlett' has been well thrown. I have seen green in M42 but not the pink that I can recall. It is Orion season so I will try to convince myself of the pink in an unfiltered view. If any object would show pink up north here, M42 would be it as large nebulae don't get much brighter than that beast up in the northern skies in winter time. M8 is 'out of season' now but it may yield pink perhaps to those who have good color detection threshold. Anyone?

[Marko]

wow. This is one of those things I guess. The 1996 picture of the homunculus nebula is on APOD today although they don't say the nebula name they are discussing Eta Carinae which is a very odd star and quite yellow although you would not know it from the picture.

[Atlas]

Hi everyone,

I have the sense that the ability to perceive colors in DSOs, especially in extended nebulae, differs individually. When I observed M 42 last year with a coobserver 30 years my junior and new to astronomy, I realized that he had difficulty perceiving the pink while to me the color was VERY clear. On the other hand he insisted on the center of the nebula being clearly green (as many observers do), whereas I saw it as gray with maybe just a slight greenish hue. In my 25" I can see M 20 as bi-color with the emission part in pink, and the reflection part blueish but always on the brink of switching to gray. Over the years I have come to believe that my eyes are more sensitive to red in DSOs than to other colors.

Johannes

[Howard B]

Color perception in anything of the than bright planetary nebulae has always been a subtle thing for me, and that’s only been since 1991 when I started using 20 inch and larger scopes. Here’s a list of what I’ve seen in emission nebulae, all using low powers around 100x:

M42
I always see the brightest part of the nebula around the Trapezium as a distinct electric green and only detect pink in the area outside of this when the sky is particularly transparent. The sky doesn’t even have to be super dark either as I’ve seen the pink under SQM skies of 21.2, although 21.95 shows it much better! The brighter parts of wings come across as a dark brick red-ish-brown and everything else are shades of grey. Some are warm shades and other slight cool, but for the most part just grey of different intensities.

M20
I generally see the red part of the Trifid as a very warm grey and on a few occasions as a very unsaturated red. The blue part is always a neutral grey to me.

M8
I have yet to perceive any color at all, which surprises me. Only a neutral grey.

M17
Same as M8, only a neutral grey.

On the other hand, the most saturated color I’ve seen in a DSO was this past summer in Campbell’s Hydrogen Star with my 28 inch. The ring of nebulosity around the central star was a distinct and saturated red when the seeing settled down, and it was a wonderful sight. The bright central star was white, so perhaps this contrast made the red look redder. Also, to see the red ring well I needed about 400x, which made the sky background that much darker so perhaps that helped contrast too.

For planetaries, the Blue Snowball is a lovely Robin’s Egg blue but all the other planetaries that come to mind are fairly similar shades of Turquoise green. Oddly, the Ring and Dumbbell don’t show me any color.

[PeterN]

Add NGC 40 in Cepheus . It is a red-colored planetary observed with my 24" scope at a dark site and shows a lot of interesting detail at high power.

[Preston Pendergraft]

I can only recall seeing color in M42 once. It was with a C14 under very dark skies in rural Nevada. I haven't really looked at M42 with large scopes.... Maybe I should more :)

[Don Pensack]

We have a few things to look out for, but one of them is the red/green trick our brain pulls on us at the limits of our vision. Many tests in labs have shown that when we view two gray rectangles side-by-side where both are just illuminated to the point where they become visible to the observer with fully dark-adapted vision, yet one rectangle is illuminated ever-so-slightly more than the other, we see the fainter one as reddish and the brighter one as greenish. The colors are false, but our brain fills them in for us.
It's unfortunate these colors also happen to correspond to the predominant colors of nebulae--reddish for the hydrogen alpha emission, and greenish for the oxygen 3 emission.
So when we see these two colors predominate in a faint nebula, suspicion of their reality should hold sway.
One good example is M27, where, when observers see colors, it is a greenish color in the brighter "bow tie" section, and reddish in the fainter outer wings running perpendicular to the bow tie. Yet, color photos show red is strongest in the bow-tie section and greens predominate in the fainter areas--the exact opposite of reported visual colors. This is probably a good example of where the colors are due to our brains' filling in the colors.

Yet, M42, at a dark site, is so bright it can damage your night vision. I've noticed a diminution in my ability to see my surroundings after viewing M42 in the eyepiece. And, under the best conditions of transparency, the nebula shows more than merely red and green colors, with the fainter section inside the ring being a dusty rose color on one side of the greenish central region, and a yellow-beige on the other. And on those nights, the nearby Running Man nebula shows distinctly blue--no greenish tint like the center of M42. Since these colors DO match the photographic ones and in exactly the same spots, I believe they are real colors, and indicate that my vision has become mesopic instead of scotopic.

I don't believe that seeing color in M42/43 requires a large aperture, but on the nights of superior transparency, when color is visible in nearly all scopes of, say, 6" and larger, the colors are definitely more intense in larger apertures. The "bow" shape of the protrusions of nebulae on either side of the central region were a distinct deep red in a 24" on a night when they appeared pale reddish gray in my 12.5".

Not too surprisingly, the blues and greens in planetary nebulae are more easily visible because our dark-adapted vision is most sensitive around 500nm at night (blue-green). Since the lens of the eye yellows as we age, providing a blue filter of sorts, it's interesting that older observers tend to see planetaries as greenish while young observers see them as distinctly blue, probably indicating the H-Beta emission at 486nm is lowered in intensity through the yellowing lenses.

[Tony B]

I, too, have seen the very distinct yellow "egg" surrounding Eta Carinae, with a 13.1" f/5 I took to New Zealand in 2000 using a 20mm Nagler Type 1. But let's not forget the pink, green and blue of M42, usually in my 22" f/4, but also recently in a 14" cat at TAAA's CAC site in southern Arizona.

As an observer who lives in the southern hemisphere I can certainly testify to seeing the Homunculus as bright yellow. Other southern colour includes the distinct blue of planetary nebula NGC 3918 adjacent to the Southern Cross and in particular the warm yellow seen in the very core of globular cluster Tucanae 47. To see this well you need 20 inch or above and the object to be over 30 degrees high. Though I will be using a 30 inch f4.5 two weeks from now at the South Pacific Star Party it is getting low this time of year so I will have to cruise the LMC and Carina instead.

[Jimi Lowrey]

Welcome to Deep Sky Forum Tony.

[Dragan]

Welcome Tony!

I'm glad to see you've joined! I hope you like your stay! ;)

[Tony B]

Thanks Jimi - I hope to welcome you to observing in Australia with the 30 inch before long. Van Robinson is developing a plan to join us at it's eyepiece for the week commencing 29 march 2014 . Van once spent an entire week using my Obsession 20 and is now an expert on the southern sky.

[Tony B]

Having fun Dragan. And when you make a trip south to Australia you won't have to bring your Obsession 25 as there will be one here alongside the 30 inch.

[Tony B]

We routinely see color in M42 in Australia when using 18 inch or above - particularly salmon color. The nebula gets very high for us, and I remember an Ohio amateur saying that when seeing Orion in Australia it was the first time he had seen the milky way passing the constellation. Kinky thing for northeners is that at this time of year we see Scorpius lengthways above our eastern horizon and at the same moment Orion hovering above our western horizon.

[PeterN]

NGC 40 in Cepheus, the "Bowtie Nebula", planetary shows a nice warmer color (grey-red) -- it is a unusual color for planetaries. Take a look at it later this summer as Cepheus rises in the NE again.

[Tony B]

Dragan - I refreshed my own memory last night before moonrise with an 18 inch Obsession classic and have to confirm that seeing a globular cluster, Tucanae 47, with distinct color contrast at it's condensed core is about as beautiful a sight as there is in the sky. Check Van Robinson's take on this. I think Omega Cenrauri high up in a 20 inch is special to him.

[Bertrand Laville]

Hi every ones,

here are the colors I perceived on three objects mentioned in this thread, NGC 7662, IC 418, and Eta Carinae.
My sketches are as real as I could, I mean to say that the colors are really the ones I perceived.

Details of NGC 7662: http://www.deepsky-drawings.com/ngc-7662-2/dsdlang/en
For IC 418: http://www.deepsky-drawings.com/ic-0418-2017/dsdlang/en
and for Eta Carinae: http://www.deepsky-drawings.com/ic-0418-2017/dsdlang/en

Clear skies
Bertrand
http://www.deepsky-drawings.com/dsdlang/en/


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[Don Pensack]

Bertrand,
In an 18", I, too, have seen the Homunculus as golden in color.
The outer parts of the nebula were a distinct pink tint at the same time.
The contrast with the gold was startling.

P.S. your 3rd link points to the wrong sketch.

[Bertrand Laville]

Bertrand,

P.S. your 3rd link points to the wrong sketch.

Oups!
Thanks Don,
Here is the right link to Eta Carinae: http://www.deepsky-drawings.com/eta-carinae-2/dsdlang/en

[Aldebaran]

Hello everyone! In 2016 I was observing with 36'' Astrofox of Tähtikallio Observatory, Finland, during the Finnish Deep Sky Meeting of 2016. During the event, we observed for example NGC 6543 (Cat's Eye Nebula). I'm quite convinced, that I observed the central part of the nebula clearly greenish-turquoise. Has anyone else observed colours in this nebula? Here is my report from the observation: https://celest1alsphere.wordpress.com/2016/12/21/observing-2-3-9-2016-in-tahtikallio-observatory/

[Bertrand Laville]

Hi All,

This PN is, indeed, very color full.
This inside is, in the usual scale of C/S, color / saturation, a very vivid blue, C130/S70 or 80, whereas the Halpha appears on the circonference, C7/S30.

Here is my sketch, and the observation report at: http://www.deepsky-drawings.com/ngc-6543-ic-4677-2/dsdlang/en

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Clear skies
Bertrand
http://www.deepsky-drawings.com/dsdlang/en/