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Stars and planets...

#1
Hello.

They say that we can't see green or purple stars, although they exist. Green stars will be perceived as white by our eye, while purples will appear as blue.

But here is a proper explanation:
Are there any green stars? If not why? I know that a star's color is based upon its temperature. Stars seem to exist in every other color in the visible spectrum. Why not green?

Your question is a good one! I actually asked one of my astronomy professors about that once, because it is true that the color of a star depends on its temperature, and stars with a wide range of temperatures do exist. The answer is that there are stars that are green, that is, they emit their peak radiation at a wavelength that we define as green. In fact, the sun is a yellow-green star so is close to that temperature.

However, stars emit radiation over a broad range of wavelengths, and the human eye is most sensitive to yellow and green radiation. When a star is green, it is pretty much right in the middle of the visible spectrum. It is radiating strongly at all visible wavelengths, with most of the radiation right in the middle. When we look at the star, then, all these colors are mixed and the result is the color white. So you won't ever see a green-looking star through a telescope.

There are also purple stars, which emit peak radiation in the violet part of the spectrum. But we don't see purple stars either because the human eye is more sensitive to blue light than to purple light. If a star is emitting a lot in the violet, it will also be radiating in the blue, and so these stars look blue to us. This is why the colors that we see for stars are:
red
yellow
white
blue
with red being the coolest stars and blue the hottest.
Source: http://curious.astro.cornell.edu/question.php?number=14
I take no credit for this.

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Also, it appears that our own Sun, which for a long time we believed to be an average sized star, it not average at all. About 2/3rd of the stars [in our galaxy] are of the Orange Dwarf type, which are much, much smaller stars than the Sun is.
Although there are true mind-blogging monsters out there (stars the size of make the Sun appear like a grain of sand next to a hippo) they are rather the exceptional case. If we exclude such exceptions, our Sun places itself among the biggest stars to be found, and of course they are not so common.

I found an interesting documentary on youtube: Alien Planets Like Earth [2014 Documentary] NEW -- 54 min.
They don't just talk of planets and the Kepler project. Every few minutes bits of less common knowledge about stars and the planets orbiting them are given. Very very informative.

Regards.

Re: Stars and planets...

#3
Huh, I actually didn't know that. That's pretty interesting actually, since we just learnt about the properties of stars at school for a regents. Besides that, I'm not sure if that would add any game play value to it. Maybe you have some radiation sensor to figure out the true color of it? I'm not sure what that adds. Nice find though!
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Re: Stars and planets...

#4
Also, it appears that our own Sun, which for a long time we believed to be an average sized star, it not average at all. About 2/3rd of the stars [in our galaxy] are of the Orange Dwarf type, which are much, much smaller stars than the Sun is.
Actually, it's red dwarfs you're thinking of. (Astronomy buff since the age of 3.) Orange dwarf stars are relatively uncommon. The sun itself is a yellow dwarf star, informally, or a G2.

Technically, G-class stars are actually white too, but we perceive them as yellow just because most of the visible radiation is in the yellow band of the spectrum. So, our sun is white. Neat to know. Our eyes are weird. Also part of perceiving it as yellow is due to atmospheric scattering. Also interesting: most pictures NASA releases to the public of the sun are false-color images, turned yellow, or orange, because we have it so firmly ingrained in our minds that it's yellow, that for some people - if it isn't yellow, they don't think it's real. Go figure - reality is unrealistic.
Although there are true mind-blogging monsters out there (stars the size of make the Sun appear like a grain of sand next to a hippo) they are rather the exceptional case. If we exclude such exceptions, our Sun places itself among the biggest stars to be found, and of course they are not so common.
The first part is true, if you meant mind-boggling. (although I would say closer to a beach ball next to a grain of sand.) Yeah, there are some pretty big stars out there - particularly O-class blue giants. Those are large (and hot!) to the point that if our sun was one, our farthest planets wouldn't be frozen.

The sun is still a relatively average star, though, if you exclude both supergiant and dwarf stars. There are larger stars than the sun, and easily - it's not the standard, nor is it the exception. In fact, our sun is even smaller than Alpha Centauri A (although slightly larger than Alpha Centauri B). (that's the nearest star system, if you didn't know - probably did, but thought I'd include that tidbit anyway.) Also, there's an entire class of stars - white (non-dwarf) stars - that are larger than the sun, yet still appear about as frequently. That's why people say the sun is an average star.


Finally, there were stars colored green in Freelancer. That annoyed me to no end. I really don't want that in LT. :\ Let's keep at least the colors a little realistic. I don't want to find a system with a green or purple star.

edit: typo.
Last edited by Talvieno on Tue Jun 03, 2014 6:42 am, edited 3 times in total.
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Re: Stars and planets...

#5
the fact that the colors of stars are predominently a small set of colors is interesting. why cant a star shine green, if it has enough of the right wavelength the green would overpower the other colors. just thinking of a color gradient tool.
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Re: Stars and planets...

#6
It's because the human eye is more sensitive to certain colors. If a star is emitting large amounts of radiation in the green spectrum, it is also emitting large amounts of radiation in the yellow, and our eyes perceive it as yellow. The same with purple: If the star is emitting purple radiation, it is also doing the same with blue, and we perceive it as blue. Because of this, it makes no real sense to color stars green because we'd see them as yellow anyway - it breaks the suspension of disbelief because we're not accustomed to seeing green and purple stars.

If you want to be so accurate, however, it would be wise to point out that even these colors are illusions, and that not only do "green" and "purple" stars not exist - neither do "red" and "white" stars, or any other color - we merely define them as such. A star's "color" is merely what we perceive from the wavelength of the emitted light. In fact, the sky isn't blue, blood isn't red and grass isn't green - it's all our perception of wavelengths, and it's what we're accustomed to. Red paint is only red because your eyes are perceiving the lower wavelength of the reflected light as red: the red paint absorbs light of other wavelengths. That's why a white surface can appear any color of light you shine on it - it reflects all wavelengths of light, while a red surface mostly reflects light in the red wavelength. Black surfaces absorb light of all wavelengths, and therefore we see little to no reflected light, and they look dark.

But really, there's no point in going that far in a game, because we do see what we refer to as "colors", and ignoring this fact just makes things seem strange.
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Re: Stars and planets...

#7
Talvieno wrote:It's because the human eye is more sensitive to certain colors. If a star is emitting large amounts of radiation in the green spectrum, it is also emitting large amounts of radiation in the yellow, and our eyes perceive it as yellow. The same with purple: If the star is emitting purple radiation, it is also doing the same with blue, and we perceive it as blue. Because of this, it makes no real sense to color stars green because we'd see them as yellow anyway - it breaks the suspension of disbelief because we're not accustomed to seeing green and purple stars.

If you want to be so accurate, however, it would be wise to point out that even these colors are illusions, and that not only do "green" and "purple" stars not exist - neither do "red" and "white" stars, or any other color - we merely define them as such. A star's "color" is merely what we perceive from the wavelength of the emitted light. In fact, the sky isn't blue, blood isn't red and grass isn't green - it's all our perception of wavelengths, and it's what we're accustomed to. Red paint is only red because your eyes are perceiving the lower wavelength of the reflected light as red: the red paint absorbs light of other wavelengths. That's why a white surface can appear any color of light you shine on it - it reflects all wavelengths of light, while a red surface mostly reflects light in the red wavelength. Black surfaces absorb light of all wavelengths, and therefore we see little to no reflected light, and they look dark.

But really, there's no point in going that far in a game, because we do see what we refer to as "colors", and ignoring this fact just makes things seem strange.
To add to this, the colour magenta doesn't even exist. :shock: It's your brain trying to wrap around the visible colour spectrum (between ~700 nm red and ~400 nm blue light iirc?).

But yes, please for the love of all that's good, do not put green and purple stars in LT.

Re: Stars and planets...

#8
ThymineC wrote: To add to this, the colour magenta doesn't even exist. :shock: It's your brain trying to wrap around the visible colour spectrum (between ~700 nm red and ~400 nm blue light iirc?).

But yes, please for the love of all that's good, do not put green and purple stars in LT.
Magenta as specific wavelenght doesnt exist no.

But its less of an out of boundary error but simple superposition of colors.

Its schrödingers color, red and blue at the same time :ghost:

Re: Stars and planets...

#10
I think a star that appears white, but gives just the slightest green or purple color on objects in the system would look fantastic!
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Re: Stars and planets...

#11
I happen to like fantasy color stars. But I'm really hoping we can get elbow-deep into the generation factors and make our personal Universe have all colors of the rainbow, or as realistic as we want to have. Ohmygod this got me so hyped now >.>
Well, if not, there is still the dev object editor, right?

Also, now that this came up, this has been gnawing at me for a while now: do 'black stars' exist(or can they in theory)? In the sense that they are so hot, their blackbody radiation equivalent color is out of the visible spectrum, somewhere in UV, and emit negligible amounts in the visible part.
panic

Re: Stars and planets...

#12
Mistycica wrote:Also, now that this came up, this has been gnawing at me for a while now: do 'black stars' exist(or can they in theory)? In the sense that they are so hot, their blackbody radiation equivalent color is out of the visible spectrum, somewhere in UV, and emit negligible amounts in the visible part.
I love this idea so much.

"Hey, this system is barren"

*flies towards center, alarm klaxons go off in cockpit* "Approaching star"

That would be awesome.
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Re: Stars and planets...

#13
DWMagus wrote:
Mistycica wrote:Also, now that this came up, this has been gnawing at me for a while now: do 'black stars' exist(or can they in theory)? In the sense that they are so hot, their blackbody radiation equivalent color is out of the visible spectrum, somewhere in UV, and emit negligible amounts in the visible part.
I love this idea so much.

"Hey, this system is barren"

*flies towards center, alarm klaxons go off in cockpit* "Approaching star"

That would be awesome.
Haha! Well hopefully we gonna get system gravity mapping or something to avoid having to get a visual down to the last rock :P I could even imagine this 'star' having a little violet glow, like spotting an UV lamp from the corner of your eye. Artistic, if not terribly superaccurate.
And I'd absolutely love something like this - built in false colors for your sensors!
panic

Re: Stars and planets...

#15
Cornflakes_91 wrote:Blackbody radiation never leaves the visible spectrum again.

Even tough the majority of the radiation might moves to UV there will always be enough energy in the visible area that you cant overlook it
Ok fine, a system of planets that "orbits" a black hole...
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