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

[Renato1 (Renato)]

Originally Posted by mental4astro

Here's something I've been pondering for some time (meaning of life can wait a bit longer... ). 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.

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 (Sam)]

Originally Posted by Renato1

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

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.