Would we see colour in a nebula if we were right up close to one?

[mental4astro]

Here's something I've been pondering for some time (meaning of life can wait a bit longer... :rolleyes:). Long exposure photos, and even with just highly sensitive CCD's we can see colour in nebulae. Even with a big dob we can see pink and blue coming of M42. But, if we were much closer to a bright nebula like M42, would our eyes be able to detect any colour coming off it? Just our naked, unassisted eyes. Colour or not?

Mental.

[SamD]

Don't see why we wouldn't see naked-eye colour. As long as most of the nebula was bright enough to be detected by the cone cells in our eyes, we would see some kind of colour.

Shame we don't have more sensitive eyes though - would be awesome if Orion looked something like this:
http://www.crystalinks.com/orion.html

[Dboots]

Hi Mental,

I have read that the answer is no and I will try to post a reference.

The basic principle is that the diffuse gas will become less and less visible as you get closer. You start to see more empty space.

It is a bit like how we see the individual stars rather the grand structure of our local part of the milk way.

Duncan

[BPO]

This is correct.

[Steffen]

I think there would be a certain distance range where M42 could be seen in colour, but right next to it (or in it) probably not. Kind of like the air around us doesn't look blue.

Cheers
Steffen.

[RickS]

Duncan is correct. Nebulae don't get any brighter (and hence more colourful) as you get closer. Up close you receive more photons but the object subtends a greater solid angle. The two effects cancel each other out and the surface brightness remains the same.

Here's a reference: http://www.universetoday.com/99989/in-reality-nebulae-offer-no-place-for-spaceships-to-hide/

Cheers,
Rick.

[Dboots]

Below is a link to an article on Universe Today:

http://www.universetoday.com/99989/in-reality-nebulae-offer-no-place-for-spaceships-to-hide/

If also has a clip at the bottom with Phil Plait giving a decent explanation.

Duncan

EDIT: (Damn Rick, you posted while I was typing...)

[N1]

I was thinking the same thing. Looking at a distant galaxy, one might be forgiven for thinking that the night sky must be incredibly bright to an observer within the Galaxy. Of course, the view is much more likely to be similar to what we see from here.

[PeterEde]

If a 30 sec exposure brings out colour then why wouldn't our eye if we was close enough for it to fill a window? We don't see colour due to our eyes construction but if close we would not need long exposure to see it

[N1]

You could simulate that by looking at a rainbow with your dob and a wide angle EP. Chances are you will see less colour than unmagnified.

[el_draco]

I doubt you'd see much colour at all; certainly not NB type. Receptors in our eye's dont detect the wavelengths. It would probably look pretty much like what you see visually through a scope, only brighter but that would only be the case up to a distance where the rarification of the gases / dust became a factor.

[ralph1]

I observed a rainbow in binoculars once hoping to see more colour. Needless to say, I was very disappointed:sadeyes: On a similar note, a telescope, even with very high transmission optics can only ever decrease the surface brightness of an object. You see faint objects better because they appear larger and activate more receptors in your eye. Ralph

[RobF]

I was actually reading an answer to this in an old Astronomy mag this morning. What Rick says was the response - basically no.

They did comment however that if there was an increase in local dust there might be a dimming of distant stars or very faint glow from some parts of the sky.

Up on Maleny during XMAS hols there was a day we drove up into clouds (really more like fog). From outside the clouds seem very thick, but once inside you can dimly perceive the moisture moving past and distant views disappear. And that would be an incredibly greater density of matter I expect versus a neb.

I wish the damned moisture over the top of me right now would disappear dammit....:mad2:

[mental4astro]

Thanks for the many replies, folks! There's quite a difference between immediate intuition and then with a bit of logic and thought.

Blasted Star Trek! Now I need to work out how to cancel my order for a warp 7 personal space craft... :mad2:

[mental4astro]

Rob, you mentioned fog. I've always been fascinated by the way fog changes in appearance depending on:

1, when you are outside of it and the relative direction of the fog and incident light with you. It can either look like a fluffy white cloud or smog.
2, when you are inside the fog, the many variations in density and particle size. Can be very eerie. Sometimes you get soaked in moments. Other times barely wet. And the appearance can be something from the sweetest dreams or unearthly. Magic stuff.

[Steffen]

But..., maybe the Mutara nebula is different, what's its catalogue number anyway? I guess something like that is only required for hiding from serious, genetically engineered villains. If you're trying to hide from your wife, I've got a fog machine I can lend you :lol:

Cheers
Steffen.

[xelasnave]

The density of objects we pbotograph are such that up close you won't see much but given we will never get there imagine it with all the colour.I

[Steffen]

Oh, I can attest to that. Every holiday destination I had picked from postcards turned out disappointing.

Cheers
Steffen.

[ralph1]

Would it in theory be possible to replace the lens of the human eye with a larger, artificial lens, say 20mm and use that to see fainter objects and possibly colours? Even better, remove the lens entirely and have the telescope focus light directly onto your retina.

[xelasnave]

Humans see one three thousandth of the electromagnetic spectrum so we miss a little

[Renato1]

You would see the exact same colours that you see in your telescope.

Nearly all TV shows and movies showing space ships going past very colourful nebula are incorrect. The only exception I remember was the TV series Lost In Space, which used black and white photos of nebula and galaxies as space background in the show.
Regards,
Renato

[SamD]

Yes, that's because (any) telescopic views preserve the underlying surface brightness, (assuming you get an optical magnification). As Rick pointed out, travelling closer to a nebula also preserves surface brightness, so a telescope sort of simulates the real nebula view from closer.

In fact, I think closer naked eye views ought to be brighter and more colourful than telescopic views. That's because telescopic optics lose some light, things are brighter above the atmosphere, but most importantly, the interstellar medium extincts magnitudes by around 1.8 VMag per kpc near us (according to Wikipedia !)

I've read that our eyes need about VMag 16/arcsec^2 to start perceiving colour. The core of M42 is about 14.5/arcsec^2. Things are a bit more difficult to calculate for say the Eta Carinae Nebula, or even the Tarantula Nebula, since although their surface brightness is down at about 16-17/arcsec^2, there's a bigger amount of amount interstellar extinction to add back if we could get closer (compared to M42). Some planetary nebula may even show some colours, the Bug Nebula has pretty high surface brightness at its core. Ring Nebula is also quite bright.

All in all, yes, I still think we would see colours closer to the intrinsically brightest nebula, but it's probably more like green to grey wispy tendrils than the full on multi-colour sci-fi nebula clouds.

[cathalferris]

The nebula are just (in general) not bright enough to activate the cone structures in our retinas. If you were closer to the nebula, it would be larger and easier to see, but still not bright enough to show colour. It would have the same surface brightness as when looking through a scope with the same exit pupil as your dark adapted eye pupil size.

If it showed colour in the eyepiece, it may show colour when physically closer. Our eyes are certainly sensitive to the nebula emission, it's just not bright enough to show colours. Exceptions are certainly possible, with the green hue of the “Huygenian Region" and tinges of H-Alpha in the wings both in M42.

In general, if you do not see colour in the eyepiece, you will not see colour when physically closer.