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03-20-1999, 03:37 PM
Astronomy books say stars come in different colors depending on their size/age/temperature. They can be red, orange, yellow, white, or blue. I've always been curious- any green or purple stars out there?

03-20-1999, 05:30 PM
I've always been curious- any green or purple stars out there? -- JKB

I suppose Dennis Rodman and The Asshole Formerly Known as Prince don't count...


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The Dave-Guy
"since my daughter's only half-Jewish, can she go in up to her knees?" J.H. Marx

03-20-1999, 05:52 PM
any green or purple stars out there?

Nope. The horseshoes are purple, and the clovers are green.

03-20-1999, 06:04 PM
JKB
Member posted 03-20-99 03:37 PM
any green or purple stars out there?

Plenty of green stars on the lapel of Esperantists.

Cheers!
-Chip

03-20-1999, 07:28 PM
Astronomy books say stars come in different colors depending on their size/age/temperature. They can be red, orange, yellow, white, or blue. I've always been curious- any green or purple stars out there?...JKB
The color of a star is determined by the temperature of it's surface (photosphere), JK. The hot ones are blue-white, the "cool" ones are red.
There are quite a few, including Vega, that put out quite a bit of their energy in the green part of the visible spectrum. The problem is, we can't see it due to the makeup of our eyes.
This gets a little complicated here, so I'm going to try to send a link. Dr. Odenwald can explain it much better than I.
http://image.gsfc.nasa.gov/poetry/astro/q72.html
Gosh, I hope this link works.

+Ron
"My first link! Hope it isn't 'missing'."

03-21-1999, 08:33 PM
There are quite a few, including Vega, that put out quite a bit of their energy in the green part of the visible spectrum. The problem is, we can't see it due to the makeup of our eyes. +Ron

I beg your pardon. I never wear eye makeup. You obviously don't know what you're talking about, and decided to jump into this thread with fabricated information that you --
Oh. Wait a minute. I get it.
Sorry.

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The Dave-Guy
"since my daughter's only half-Jewish, can she go in up to her knees?" J.H. Marx

03-24-1999, 12:45 AM
I've always been curious- any green or purple stars out there? --JKB
"I do not like <FONT COLOR="GREEN">Green Stars</FONT> and Spam!"

<FONT COLOR="GREEN">ExTank</FONT>
"And that was the last[i] time I bought the food for our camping trips"[/i}

03-31-1999, 08:24 PM
You see a "green" star every day, believe it or not. Our very own sun puts out most of its light in the green section of the visible light spectrum. Why we don't SEE the green has to do with how intense the light given off by the sun is (billions of photons per second) and the Earth's blue sky. <S>

-- Sylence

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"A friend of mine once sent me a post card with a picture of the entire planet Earth taken from space. On the back it said, 'Wish you were here'." - Steven Wright

dougie_monty
11-24-1999, 03:53 PM
Longe vivu la verda stelo! :)

starfish
11-24-1999, 10:00 PM
There are no green stars. Go to dejanews and do a search in sci.astro.

Stars that put out a lot of green light put out even more light of another color.

# 00: The Fool
11-24-1999, 10:14 PM
Plenty of green stars on the lapel of Esperantists.


Huh?


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"Oh we were brought up on the Space-Race, now they expect us to clean toilets. When you have seen how big the world is how can you make do with this?"
Pulp, "Glory Days"

scr4
11-24-1999, 11:04 PM
The short answer is that a star cannot emit green light without also emitting a lot of blue and red light, making it look white.

To be more exact, light radiated by a hot object is called a "blackbody radiation." Its spectrum is determined only by its temperature. For everyday objects, like human bodies, the peak is in a very long wavelength, i.e. infrared. That's why infrared cameras can detect body heat. A burning charcoal has a higher temperature and the peak is somewere in the infrared or long-wavelength visible light (i.e. red light). Incandescent light bulbs and cool stars are around 3000 degrees and emit reddish light. A 6000-degree star like our sun has its peak in the green light, but green light is between red and blue, and the blackbody radiation has a wide enough wavelength range that our eyes see a lot of blue and red light as well. A star even hotter than the sun has its peak in the blue band, and doesn't emit much red light, making them look bluish.

So it is impossible to get green light by just heating up something. You have to either use molecules that selectively absorb red and blue light (green paint, green filter), or use some other mechanism to generate light, i.e. laser or LED.

Another way to look at it is that the Sun is what our brain/eyes use as a definition of white. A star hotter than the sun emits more blue light and less red light than the sun, so it looks blue. A star cooler than the sun emits more red light and less blue light, making them red. And there's no other parameter you can change on a star.

EvilGhandi
11-25-1999, 02:53 AM
scr4,

You state, "So it is impossible to get green light by just heating up something."

Maybe I misunderstand you, but i recall a little experiment from 7th grade physical science class. We dipped a wire loop into various chemicals and observed the color change when we heated them in an alcohol flame.

I remember distinctly that cobalt chloride produced blue light, strontium nitrate produced red and copper sulfate, green.

Or did I miss something in the context of your reply?

scr4
11-25-1999, 10:06 AM
Sorry, I guess I wasn't very clear on that.
What I meant that a "thermal radiation" or
"blackbody radiation" cannot be green. However, "non-thermal" radiation often radiate in only one frequency and have very pure colors. They are produced by a specific ion under special circumstances (i.e. the right temperature and density for the ion to exist), like the experiment you cited. Neon signs and fluorescent lights are also examples of non-thermal radiation.

Actually the sun and other stars do produce many emission lines and absorption lines as well, since there are ions and plasmas of all kinds on the stars. But none of them are strong enough to contribute much to the overall color, at least in the visible wavelengths.

Monty
11-27-1999, 01:30 PM
Dobule Oh: the green star is the symbol of the international Esperanto movement.

WallyM7
11-27-1999, 01:57 PM
We dipped a wire loop into various chemicals and observed the color change when we heated them in an alcohol flame.

There ought to be a law against wasting alcohol like that.

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This space for rent.

NanoByte
11-27-1999, 08:00 PM
I think the OP is basically answered at this point, so I'll pick up on that little tangent:

the green star is the symbol of the international Esperanto movement.

OK, so why is it such?

Ray (I thought Esperanto was originally intended to cover the whole spectrum. ;-) )

Sunspace
11-28-1999, 10:42 AM
the green star is the symbol of the international Esperanto movement
Longe vivu la Movado!

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"Kiu frenezas? Cxu la mondo aux mi?" -Persone