Does red stars give red light?

[Artlav]

I've been playing around with stars in oglaclient, and got some weird results from different colours.

What would it be like on the planets with red or blue stars?
Our sun is supposed to be yellow, yet it gives pretty much the white light.

I'm trying to base on Harvard spectral classification, but can't get actual apparent colours closer than "blue, light blue, yellow, white, etc". How would it look like and what does it depend on?

A G2 star is on the third image below, said to be yellow, and that doesn't quite add up in what it looks like. I suspect that their light will appear mostly white to a human, with slight variations, but how slight?

Summing up, anyone know a good read on the subject?

 

[T.Neo]

Yes, red stars give red light. That's why they're red stars.

But it would not be a deep red. It'd just be further to the red end of the spectrum- the star would still be pretty bright.

Light from cooler stars (K or M) would probably be recognised by an uninitiated human as indoor light.

I've read somewhere that O stars might evaporate preplanetary disks, thus preventing planets from forming. Brighter stars also put out more UV and have shorter lifespans, and thus would be less likely to have native life.

 

[RisingFury]

Stars basically emit black body radiation. A body with a certain surface temperature will spread it's spektrum out over a lot of wavelengths, but it will have a distinct peak somewhere. The function that describes the spectrum is called Planck's law.

I would write the formula, but this one is nasty, so here's teh wiki link:
http://en.wikipedia.org/wiki/Planck's_law

As you can see from the graph on the side, the hotter the body is, the shorter the wavelength of the peak is.

A colder star will have it's peak in the IR / red frequencies so we will see it as red, but that doesn't mean to just crank up the R to 255 and neglect the other two...

A hotter star will have it's peak in the yellow and green region, such as our Sun... the reason there are no green stars though, is because the spectrum gets spread out over the entire visible light, so that it comes out white to our eyes.

A hotter even star will have it's peak in the blue / violet / UV part of the spectrum.



I know this doesn't give much in terms of RGB values, but I know there is a conversion possible. It's offten used in astronomy, when a real color photo in needed. At least this should get you started...

 

[martins]

Does anybody have a reference for the spectral distribution of RGB components from a typical monitor? This essentially looks like an optimisation problem:

Let's say the colour spectra of the RGB components are given by
[math]r(\lambda),\; g(\lambda),\; b(\lambda)[/math]
then for a triplet X = [R,G,B] of colour values, the complete spectrum would be given by
[math]I(X,\lambda) = R r(\lambda) + G g(\lambda) + B b(\lambda)[/math]
Now given your 'target' spectrum
[math]I_t(T,\lambda)[/math]
from a blackbody ratiating at temperature T, you want to find X such that an objective function, e.g.
[math] \Psi(X) = ||I(X)-I_t||^2 \rightarrow \mathrm{min} [/math]
You find the minimum by solving
[math]\frac{d\Psi}{dX} = 0[/math]

 

[McWgogs]

This: http://www.vendian.org/mncharity/dir3/starcolor/
There you have the rgbs and all.

Also keep in mind that human perception of color is dynamic so these numbers are probably too saturated.
And yes, the class M star is a light bulb, so callibrate on that.
Try to make the M star's light to appear like a bulb lit room.

 

[Artlav]

This: http://www.vendian.org/mncharity/dir3/starcolor/
There you have the rgbs and all.

Nice, thank you!
It actually gives plausibly looking colorations, some saturation reduced.

With this, an M8 star looks like that:

That was this before:

 

[McWgogs]

What rgb is that? doesn't look like anything from that page.

Try R255 G221 B190 for a M6 star. That's the color from that web page, edited so the numbers are halfway to 255. Here's the whole thing for reference: http://img705.imageshack.us/img705/6308/colorsx.jpg

 

[Artlav]

What rgb is that? doesn't look like anything from that page.

Hm, curious. That was supposed to be this:

And, R255 G221 B190 gives that:

Which is essentially white.
Also, i've answered apparently your comment in spaceway gallery page, which you might find interesting wrt this thread.

 

[SiberianTiger]

Artlav, is it possible to leave the visible disc of the star white and fill the halo only (gradientally outwards)? In my view, that would give a best imression of a coloured but still bright light source?

 

[McWgogs]

Yeah, the first one does look better. And big thanks!