Full Colour Galaxy / Nebula Observing?

[stevetynant]

Newtonian telescopes basically follow the same design now as those constructed by Isaac Newton in 1668 over 350 years ago (I know there are improvements but the basic blue print is the same)

Given the slow rate of improvement in this particular area seems to be diametrically opposed to the rate of technological advance in most other fields is there any possibility at all that in the future there will be telescopes capable of visually observing (not photographing with long exposure) Nebulae / Galaxies in the same wonderful colour images we see from members photos on this forum.

What would be the single thing that would make this impossible - if indeed it was impossible (at the moment at least)

I am a firm believer that if you can imagine it - someday it will happen and though I speak with no technical knowledge on this issue at all I know theres a lot of you well clued up - Would it be possible?

[acey]

No, it's not possible. Images use long exposures and in some cases (e.g. Hubble images) false colour. No telescope will ever make things look the way they do in photographs.

Let's suppose you could fly right next to the Andromeda Galaxy or Orion nebula - what would they look like? Well, we really are flying right next to a galaxy, in fact we're inside it - the Milky Way. And it's so faint that a few streetlights wipe it out completely. Andromeda Galaxy would look the same, and the Orion Nebula would have a similar surface brightness. Turn out all the lights inside your spaceship and after half an hour of dark adaptation you'd see some red in it.

Of course, that's not to say that people will never design telescopes with photon multipliers and colour enhancers that will give users a view resembling photographs. But in that case, as far as I'm concerned, you might as well look at a photograph.

The scientific way of saying all this is that surface brightness is independent of distance. Make something twice as close and you make its apparent area four times bigger, while at the same time its total light appears four times stronger (by the inverse square law). So the surface brightness or luminance ("brightness per area") is the same. A telescope makes things look closer but can't increase the amount of light that's coming from them.

The only other way to get the "photograph effect" with our own eyes would be to turn our eyes into cameras: implants that would enable the retina to accumulate far more photons before firing a nerve impulse, a huge increase of cone cells, spread right across the retina, and a big increase in their sensitivity, so that we'd see full colour in dim light conditions. I won't be queuing up for that operation.

[ollypenrice]

The problem is very easy to identify. In order to trigger the light sensitivity of the eye you need a lot of light. The solution to that is also dead easy. Build a very large aperture instrument.

Now for the difficult bit; in order not to be showing a smaller and smaller piece of sky your telescope has to have a very fast focal ratio. I would think that a one metre telescope with a focal length of 500mm would show true live colour. That would mean building a 1 metre F0.5 instrument. This cannot be done.

We need another way of collecting a lot of light and getting it into the eye. I'd have thought that it might be possible using a large number of fast, smaller instruments. These smaller instruments would have focal ratios of the 'possible' kind, around F4. But how do we get their lightpaths into a single beam to go into your eye?

Not a clue!

Because our technology has done some remarkable things we can be fooled into thinking that anything is going to be possible one day. I very much doubt this. Our biggest thanks should go to Al Nagler for pioneering ultra widefield EPs which give effective focal ratios faar shorter than were previously possible.

Olly

Edit. Acey, we crossed in the post but are essentially saying the same thing, I think. The problem is to collect more light without magnifying more, hence the need to keep the focal length of the hypothetical scope short.

[acey]

Olly - yes, we're saying the same thing, except I'd add that no focal length is ever going to solve the luminance theorem: you can't make a telescope in which the surface brightness of the image is greater than that of the object. All deep sky objects have a very low surface brightness, in comparison with objects we look at in daylight, and a telescope can't change that.

[stevetynant]

No, it's not possible. Images use long exposures and in some cases (e.g. Hubble images) false colour. No telescope will ever make things look the way they do in photographs.

I understand whats happening at the moment - I guess thats why you can look at two peoples photos of the same celestial object and see differences in the colours portayed - So agreed its not possible now - but never?

Let's suppose you could fly right next to the Andromeda Galaxy or Orion nebula - what would they look like? Well, we really are flying right next to a galaxy, in fact we're inside it - the Milky Way. And it's so faint that a few streetlights wipe it out completely. Andromeda Galaxy would look the same, and the Orion Nebula would have a similar surface brightness. Turn out all the lights inside your spaceship and after half an hour of dark adaptation you'd see some red in it.

So you would see colours - not the bright portraits I agree but it would be there - and in the future you would still need to be dark adapted - poeple often say they see a green hue in the M42 Now - is it outside all probability that there will be a technique to enhance this exponetially in the distant future?

Of course, that's not to say that people will never design telescopes with photon multipliers and colour enhancers that will give users a view resembling photographs. But in that case, as far as I'm concerned, you might as well look at a photograph.

The scientific way of saying all this is that surface brightness is independent of distance. Make something twice as close and you make its apparent area four times bigger, while at the same time its total light appears four times stronger (by the inverse square law). So the surface brightness or luminance ("brightness per area") is the same. A telelscope makes things look closer but can't increase the amount of light that's coming from them.

Hmm - I might have to admit defeat on this one

I just struggle with the word never - to think how recently (relevant)it was that Einstein came up with his laws of relativity and then not to imagine that there are things possible way outside what we currently perceive as physics is very arrogant in my opinion.

However thats why I'm an accountant and not a planning the nexy Mars mission lol - thanks for your feedback Acey - really enjoyed reading it

[stevetynant]

Olly and Acey - there is one thing I got spot on - there are people on this forum far more clued up on this than me - thanks again for the input - really interesting.