So I'm in a Spaceship..........

[Spacehead]

......... and I am drifting past the Pelican Nebula.  As I look through my window, which is clear glass, what colour is the nebula and can I even see it?

 

[JohnSadlerAstro]

I'm guessing you wouldn't see it, for two reasons.

(1). Brightness of stars within it. My logic would suggest that the contrast between stars and nebula would remain the same whatever distance you are from it. Therefore the stars would be very bright and eclipse the glow of the nebula.

(2). Wavelength. There would probably be very little visible light, and even  that would be difficult to see because of (1).

John

[Moonshane]

I think it's more to do with proximity. The overall visual magnitude will be spread over an increasingly wide vista as you approach. The Pelican is visible visually from Earth with suitably dark skies as it's relatively compact from this distance. The North America Nebula is similar as if you use a big dob with a reasonably long focal length, you often look straight through it even though it's in the field and therefore, rather counter-intuitively, it's better with a smaller aperture and wider field - and even with just a filter held to your eye at really dark sites. Assuming an object can be seen from Earth in the best conditions, there will be an optimum distance to see it best with naked eye (i.e. it needs to be big enough to see it but not so big it becomes to diffuse to see it). If it's formed of non-naked eye visible material, then it won't be visible no matter what, other than as a 'hint' maybe unless you use filters, and even then......

[michael.h.f.wilkinson]

The fact is that the Pelican has a very, very low surface brightness, and surface brightness does not change with distance. As you approach the nebula, the total brightness goes up, but so does the apparent surface area (by exactly the same factor, therefore the ratio of light to surface area doesn't change). From a really dark site, with really dark adapted eyes, I can see the Pelican and NA nebula at a large exit pupil. Combining these observations means that as I approach it, I will still need a dark adapted eye to see it, and the dark adapted eye does not see colour. If we magically boost the output of the nebula, without changing spectral content it would appear largely red (H-alpha)

[RT65CB-SWL]

My theory is that it it would look like [our] Milky May as we see it from here on planet Earth. The human eye is not that good on colour recognition in a dark enviroment that it why [we] see the Milky Way and other DSO's as grey fuzz. All the pictures [we] see of DSO's via Hubble and other orbiting telescopes/observatories etc., have been enhanced with an assortment of filters, wavelengths, processing, etc...

...then again --->

[gajjer]

I entered into a very similar discussion, a while back, thinking that as you got closer it would get brighter. However, I think Moonshane and Michael have got it right. As you get closer, it's spread over a larger area.

I would say it hurt my brain muscle for some time afterwards.

 

cheers

gaj

 

[DaveS]

In the event that you could see *anything* it would appear grey, as you would have to be totally dark adapted, which means monochrome rod vision. In any case you would only see the [OIII] emission, as the HII is beyond the rod's wavelength limit.

[michael.h.f.wilkinson]

9 minutes ago, DaveS said:

In the event that you could see *anything* it would appear grey, as you would have to be totally dark adapted, which means monochrome rod vision. In any case you would only see the [OIII] emission, as the HII is beyond the rod's wavelength limit.

You would also get the H-beta. The Pelican and NA are much brighter in a UHC filter than in an O-III, so H-beta should is probably more important than O-III in this instance (unlike planetary nebulae). The red of H-alpha would only be visible if brightness was increased to the level that cones kick in

[xtreemchaos]

no it would be cloudy  , charl. 

[DaveS]

Ah, yes I'd forgotten about H-beta. As an imager I don't bother with it as it gives no new information, and living under London's light pollution I've never tried looking at emission nebulae, apart form M42.

It'd still look grey though.

[ollypenrice]

Maybe it would be like observing terrestrial clouds which appear bright and structured from a distance but which dissolve into a general vapour as you approach or enter them.

1 hour ago, Philip R said:

My theory is that it it would look like [our] Milky May as we see it from here on planet Earth. The human eye is not that good on colour recognition in a dark enviroment that it why [we] see the Milky Way and other DSO's as grey fuzz. All the pictures [we] see of DSO's via Hubble and other orbiting telescopes/observatories etc., have been enhanced with an assortment of filters, wavelengths, processing, etc...

...then again --->

The colour seen in calibrated natural colour (L)RGB photos should be true to the object's signal from the visible spectrum. I see no reason to doubt that if we had more sensitive eyes we would see these colours to a reasonable approximation. The fact that astrophotos have strong colour as well as strong brightness arises from the camera's ability to accumulate light over time. We can collect enough colour information over time to be able to render it visible.

The colour in colour mapped narrowband images, though, is simply a visual code for identifying the gasses.

Olly

[SonnyE]

You wouldn't have Earths atmosphere to be filtering it either...

Is your window an HA? I like my HA7nm here back on Earth. Pops the red, and drops the light pollution...