Colour in dark skies?

[gaseous]

I have a mate who has just built a house south of Queenstown in NZ. Dark, dark skies by all accounts - Bortle 1, SQM 22 if ClearOutside is to be believed. Last time he was there, he maintains he could see with the naked eye a pinkish hue in the area we've now determined was the Eta Carina nebula. I've heard that young people's eyes are much more adept at seeing colour in low-light conditions, but is it possible for older (50+) eyes to distinguish colour in excellent dark skies? I ask this not to pooh-pooh my friend's claims or visual acuity (although some of his line calls in tennis leave a bit to be desired), but more to plan an observing holiday to NZ in the near future if this is indeed accurate and possible. Cheers.

[strongmanmike]

In a nutshell and for what ever reason, perceived or real (the jury is out) I would say YES.

My best astro mate and I, both in our mid 50's, have done several observing sessions from excellent dark and transparent skies, 1450m up in the Tindery mountains NSW under Bortle 1/2 skies (https://pbase.com/strongmanmike2002/eagleview_observatory_tinderry_moun tains) with an 18" F4.1 Dob and we have both concurred to being able to note weak rose and somewhat stronger green tones in bright nebulae including M42, M8 and M20 and green blue in bright planetary nebs, star colours are more vivid too, with perceptible rose tones visible in the brightest globs too.

Mike

[glend]

With his naked eye, no. Tell him he's dreaming. Seriously, willful seeing is a thing.
Perhaps with rose coloured glasses.

[strongmanmike]

Yeah, that's what we thought, been observing for 40 years and we don't see the same effect in the side by side 12" F5 dob...? The fact that we both note it, means we are both..?.. being fooled :lol:...ether way, maybe something weird going on with the rose in the nebs and globs..but a perception is still part of the viewing experience of the observer, like 3D "feels" :shrug: but the super contrasty views and vivid star colours are frikkin unreal :D...sounds like it might well be similar, or better! south of Queenstown NZ :)

Mike

[gaseous]

Thanks gents, he's not astronomically minded, so he wouldn't know what sort of colours might be visible, hence my surprise when he mentioned seeing pinkish hues. It did sound a little unlikely with the naked eye, but as I've never been in an SQM22 sky I couldn't tell if it was possible or not. I'll definitely need an NZ holiday to confirm...

[EpickCrom]

From my experiences viewing naked eye in pitch black bortle 1 skies out of Mt Magnet, 600 km north east of Perth, I can't see any colour naked eye, but the Milky way looks a brilliant white colour, just like a white cloud! Of course any real clouds look pitch black, very ominous!

I do see colour through my 10 inch dob from my backyard though, the brighter high surface brightness planetaries look a vivid green or blue. M42 looks very green, and star colours clearly stand out.

Patrick, I reckon you should book that trip to NZ:eyepop:

[gaseous]

Definitely a trip to NZ on the cards. I normally see the bluish-green tints in M42 and some of the brighter PN's, but I've never seen any of the redder colours.

[EpickCrom]

Yep, same here Patrick. I've haven't yet been able to see the red tints in M42 or in the planetary IC 418 that some other observers have seen. I have however once seen a pinkish hue in the Eta Carina Nebula on a night of exceptional transparency when it was at the meridian.

I haven't been able to repeat that observation since!
.

[mental4astro]

Yes, I can see M42 in full colour of greens, blues and pinks.

For anyone to say no colour can be seen is only because they do not so no one else can and denies the experience of everyone else who does. And the colour that is observable is also variable for physiological reasons, greens, blues and pinks. You need to understand how the human eye functions to understand how and why colour is visible, and why some people don't

To maximise your chances of seeing blues, greens and pinks in M42 you need to match the maximum exit pupil for any given scope to the largest diameter of your pupil. This is to maximise the amount of energy reaching those cones that those specific cones that the light energy is illuminating. If there is insufficient energy density then the required response won't be triggered. This is seen in why stars can have their colour seen but nebulae far more difficult because of the much lower energy density they have. Aperture is also a factor as scopes are made to collect light - energy - and the larger the aperture the more light and the greater the energy density entering the pupil. Make the exit pupil too large or too small and the energy density reaching the illuminated cones won't be enough to trigger the required reaction. Which is why with a small exit pupil everything is seen in black and white. And the exit pupil can also vary over time for reasons that are explained below.

The eye has rods and three different sets of cones in the retina. Each of these has a different trigger threshold - so if the necessary amount of minimum energy is not reached, then there will not be a response from those cells. Rods have the lowest threshold, which is why under low illumination we see things in black and white. The green cones have the next highest threshold, which is why most people will see pale greens in nebulae through the eyepiece. Blue cones have the next highest threshold, a little higher than that for green. Red cones however, their threshold is not the same gradient up like between green and blue. Their threshold is a fair bit higher and why pinks/reds are very difficult to see under low illumination. Understand this aspect and the reason for why the appropriate exit pupil is required to trigger the appropriate colour response. AFOV is of no consequence as it is the actual illuminated area on the retina that is reacting to the stimuli of the light, not the retina in its entirety.

There are many factors that influence why some people don't see colour at low levels of illumiation.

* Age. As we age our pupils get smaller in diameter. This means that your ability to see colour in nebulae also reduces over time. So if you came to astro in older years, you may have come with a pupil diameter that won't permit enough light to get in no matter what exit pupil you use, along with other factors below.

* Gender. Colour blindness is common in males. Around 1/3 of males have some level of colour blindness, from angle's breath through to no colour perception at all (very rare). Yet colour blindness in females is rare.

* Health. Eye health has a major impact on the ability of the eye to function properly. Diseases such as diabetes is diabolical on eye health as are others. Drugs (both medical and illicit) along with alcohol and smoking are also factors that affect eye health, and hence for the eyes to function properly.

* Genetics. Something that we have no control over and may either take away ones ability to see colours or actually enhance this ability (lucky sods).

* Fatigue. This is one factor that is next to always ignored as a factor influence visual performance. Power naps are a good tool to help refresh one's eyes and one's overall performance at the eyepiece.

With people who insist that no colour can be seen through the eyepiece, when you dig a little deeper you will find that they are male, typically older and have factors that compromise their ability to see colour at low illumination or are even colour blind. Yet they feel entitled to deny the experience of everyone else.

I have always been able to see greens and blues in nebulae, of course depending on the brilliance of the nebula. I have also seen M42 in full colour of greens, blues and pinks. The first time I saw this was during first light with my 17.5" dob using a 30mm eyepiece. It blew my socks off this surprise. No "averted imagination" as this was not something that I had ever imagined possible. 10 years later as my sketching ability developed I revisited M42 to sketch it in full colour, I used the same scope/EP combination and to my great sadness I no longer could see those pinks, only the greens and blues :( I thought I had lost those pinks for good.

A couple of more years and our Club has a new member, an ophthalmologist. With this I start picking his brains about how the eye works (see above) to work out practical ways in which to optimise response at the eyepiece and to work out better ways to see in the dark without compromising dark adaptation (which means I now use dim orange light to sketch with and read instead of painfully bright red which has very poor contrast and does affect dark adaptation).

Conversations with this member also encouraged me to revisit M42 with the idea that maybe it was contemporary eyepiece coatings that cheated us of this ability. So with five very experienced observing buddies we set up three scopes and armed ourselves with a bucket-load of eyepieces at our Club's dark site. The scopes we set up were my 17.5" f/4.5 dob, an 8" f/4 Newt and a 10" f/12 Mak. I was wrong about the coatings...

To our amazement five out of us six people were able to see greens, blues and pinks in ALL three scopes! Yes, including the Mak! For me with my dob, it was needing to use a 24mm eyepiece, not a 30mm as I used 12 years prior. My pupils had reduced in size in that time so the optimal exit pupil for a full colour response had reduced. However, the colours were not as vivid now as they were all those years ago, in particular the pinks. With the f/4 Newt, I had to use a 22mm eyepiece to see all the colours. With the Mak, it required a 50mm eyepiece, and PRESTO! the greens, blues and pinks were all there!

One of my observing buddies though was not able to see any colours at all through any scope no matter what eyepiece was used. But he has significant health issues and is taking an extraordinary number of medicines. We all felt disappointed for him, but he proved to be an important control in this exercise.

I know of two people who have been able to see pinks in Eta Carina, one a 20 year old woman the other an older amateur astronomer. At outreach events I try to ask participants what colours they can see in M42 and Eta Carina. If the crowd is not too big I may also swap between eyepieces. Age is certainly an immediate factor that is seen in people's ability to see M42 in full colour (other personal factors not being discussed), and Eta Carina is certainly a difficult one to see more than pale greens and blues (as I do).

Planetary nebulae can also show colours, namely greens and blues. The Blue Planetary being the most obvious, named for its distinct hue (but apparently some people will still continue insisting that no colour can be seen through the eyepiece...). The planets, certainly show plenty of colour, but they are also extremely bright. And I have already mentioned stars showing colour.

Aperture cannot be forgotten here. I mentioned it only briefly but it is a BIG factor for its sole purpose of collecting light. f/ratio is inconsequential as it is actually exit pupil that affects energy density. But aperture grants this energy in the first place. There are astro sketchers who make use of some very large apertures, in the order of 30" and larger, that are presenting works of nebulae other than M42 in greens, blues, pinks and even yellow and orange. Make the aperture too small and of course the amount of energy is just not there to trigger the necessary response from our eyes.

So, yeah, full colour can be seen through the eyepiece, if a number of factors are satisfied and if the object is bright enough.

Alex.

[gaseous]

Thanks Alex, that's very interesting to know about the maximum exit pupil size, and the dim orange light. I have found I need to have the screen on my tablet quite bright (and obviously red) to read it, so this may tend to deaden whatever small sensitivity I may have to pinks in nebulae. Might need to try for a much dimmer screen next time.

[mental4astro]

Red light is a conundrum. It is useful under a dark sky, but it use also ignores an individual's ability to make efficient use of it. Its exclusive use assumes everyone's vision is the same. It has its place, for sure, but when it comes to an individual's ability to use it for very specific tasks, it can be very problematic.

I used to have no problem being able to read a chart using red light. However over the years this light had to become brighter and brighter and contrast was becoming increasingly difficult to perceive making reading harder and harder.

It was also reading a couple of articles in S&T and Astronomy magazines about using orange light in addition to red that also opened my eyes to using different wavelengths of light at night. So I experimented with different LEDs that were more orange and dimmer than wouldn't you know it, not only was I able to read & sketch much more easily with greatly improved contrast, the illumination required was much lower and my dark adaptation was preserved, actually improved because I was no longer stunning my vision with a ridiculously bright red light.

I cannot use the "night mode" with Sky Saffari - it is way too bright and totally illegible to me because there is no contrast visible to my eyes, and at its lowest illumination setting it is still too bright and forget contrast. Instead I actually keep Sky Saffari on full colour and its lowest screen illumination. The sky is not red but black and the stars and features I can regulate their individual illumination and over all its brilliance is not only lower, but contrast is better and less detrimental to my dark adaptation than the night mode is. I would prefer not to have to use full colour as I know it is not without consequence to my night vision, but I have no further tools to improve things with Sky Safari.

Red is also disastrous while trying to make your way through the dark in the bush. The problem is green foliage - it looks the same colour under red light as red itself and offers nothing in terms of contrast and safety, not only for obstacles but other hazards too, such as trip hazards.

Red is great for static hazards, but not for reading or moving about in the dark. Thanks to having an ophthalmologist in our Club's membership, my Club has a more flexible lighting policy, one that allows for individuals to use red and orange as they need. If nothing else, it is a safety aspect.

Alex.

[EpickCrom]

What an interesting thread!

Alex, thanks a lot for this information. I too find using red light problematic whilst at my bortle 1 "site". I shall try a dimmer orange LED.

It makes a lot of sense that matching the exit pupil to the maximum size of your pupil helps with seeing colours in nebulae, as well as the other factors you mentioned. An "eye opening" thread indeed!

The Blue Planetary is the bluest object ive ever seen in the night sky. It's truly an amazing object.

[Dave882]

It's been really fascinating reading everyones responses here. Unfortunately I am not able to get away to dark skies very often with my c14, and certainly from my urban locations there is practically zero possibility for seeing colour through the eyepiece - with the exception of a couple of planetary nebula and the Homunculus- so bright that a deep orange / tangerine colour can be clearly seen in the hourglass shape of the bi-polar emission.
Travelling to a B4 location, I can see plenty of green in say the NGC2070, M42. At a B2 location those colours just come to life and with plenty of blue, and yes, just a hint of pink in M42. I remember when I was in Coona last year, spending some time attempting to see the horsehead without success (even though the flame was very pronounced). I understand that this target relies on your eyes being able to pick up the surrounding red Ha emissions to be able to identify the 'hole' in them. Could have been sky conditions, or my eyes just not up to the task... but after reading Alex's comments on exit pupil that could be a factor too

[mental4astro]

My first view of full colour in M42 was from my home in Sydney. Don't discount your chances with your C14 - use a long eyepiece, around 50mm and have a go.

Seeing the Horsehead is more about the quality of transparency rather than just pure aperture grunt. It is possible to see it with an aperture as small as 6". For this to happen it demonstrates entirely how it is transparency dependent.

I have been able to see it without the use of filters using my 17.5" dob from my Club's old Bortle 4 site. I have also had nights when it remained totally invisible using the same scope and no matter what filter I tried.

Being able to gauge the quality of transparency is something of a lacking skill. Just because a location is "dark" it does not mean it provides routinely good transparency. Some people have not been able to see the Horsehead no matter what aperture they use all because the location they are using is not providing the goods. And many clubs have also failed to conduct the necessary feasibility studies for the site they are using beyond "this is a dark spot, it will do". These studies need to be done across at least a year to understand the routine quality of transparency and hopefully seeing too. The thing here is members of these clubs also assume that the relevant studies had been undertaken. In many instances they have not. Taking the site selection process a little further here, it also shows that dew and astro are not inseparable bedfellows.

Gauging transparency is something that does take time, but it is not difficult, no matter if you under a dark sky or urban. The principles are the same. Come to recognise any number of DSO's and other celestial features that are visible naked eye. How clearly or not these are able to be seen naked eye will tell you straight away the quality of transparency. This can also be done telescopically, such as with galaxies as these too are totally dependent on the quality of transparency in order to make out features within them, such as their arms or H2 regions say within M83. If transparency is down, at best you will struggle to see the arms in M83, at worst only see the core and maybe a diffuse disk, but no further structures.

An SQM will not give you any information regarding transparency. It can't. It is only a glorified light meter as it also doesn't know if the Milky Way is dead overhead or absent, and the Milky Way has a HUGE impact on how dark a site can get, which an SQM registers as an increase in the sky's brightness but not the quality of its transparency. If transparency is down, this also acts to tone down the brilliance of the sky, giving a false reading on how dark the sky actually is.

As some examples, from my Club's old Bortle 4 site, transparency was typically outstanding despite its proximity to Sydney. Uranus was not only a naked eye object for me, but I could also see fainter stars around it. The Tarantula Nebula is not only visible, but on nights of excellent transparency it stands out like a brilliant beacon along with mottle detail around it. Not just bright features but dark ones too. The Dark Horse of Sagittarius should appear so stark and distinct that you could reach up and feed it a sugar cube. From my home in Sydney, I use being able to see M8 & M20 together along with the Cloud of Sagittarius. I have DSO's and features dotted across the sky and across the year, naked eye and telescopic. The Horsehead is one such feature that I use as a telescopic gauge. From my Club's new Bortle 2 location, things are even more outstanding.

Transparency also impacts upon the ability to see colour just as it impacts on galaxies.

Transparency really is something that is not understood well enough by many amateurs.

The image below is of my sketch of the Flame & Horsehead nebulae done from my Club's Bortle 4 site using my 17.5" dob. Transparency was particularly good this night as I could make out the crook of the Horse's neck, not just a dark pimple. And yes, I sketch directly on black paper at the eyepiece. Sketch is A3 in size using white soft pastel, charcoal and white gel ink.

Alex.

[gaseous]

Thanks Alex, I read your recent works re. transparency on the Cloudy Nights forum and found it most instructive. I'd be surprised if my eyes are good enough to see the Neptune or Uranus under even pristine transparency, but you've certainly provided some excellent advice in this respect.
I also agree with you about the night mode on Sky Safari. I find it either too bright, or lacking enough contrast if you turn down the brightness. I've been using a tablet screen protector over the top, which has a red gel film applied to it, and this tends to dim things down further and add a very deep blood red tint to the whole screen, but from what you're saying, it might be worthwhile trying something with more of an orange hue. Thanks again.

[strongmanmike]

Some great info and input Alex :thumbsup:

It was the opinion of both my observing buddy and I that the clearly excellent transparency up at Eaglview, was probably contributing to our colour perception. Your point about eyepiece and exit pupil resonates too because on reflection (pardon the pun) our perception of colour has not been the same with every eyepiece and we were putting it down to FOV :shrug:

Eagleview is a great location to observe, you should come visit ;)

Mike

[mental4astro]

There is one RED object that all too often forgotten about, but is without rival as a DSO with unmistakable colour - the Homunculus nebula.

Its distinct red-orange colour is noticeable through binoculars. With a scope its mottled structure is not only visible but so too is the variation in its red-orange hue, in the lobes and the tutu of material coming out from between the two lobes. So distinct and remarkable that all of this does not need a dark sky to see it.

The sketch below was done using my 9" Mak from my home in Sydney. It is an early attempt of mine in working out the technical challenges this particular object presents to me as it is so far removed from anything else in the night sky.

Alex.