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Why are there no green stars?

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20 years 10 months ago #479 by voyager
Replied by voyager on topic Re: Why are there no green stars?
Stars do NOT radiate as black bodies because the reactions happen deep in the core of the star, NOT in the photosphere so the make up of the star WILL affect the light it radiates.

This we know for a FACT because we used the spectrum of the sun to show that it is made of Hydrogen!

Bart.

My Home Page - www.bartbusschots.ie

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20 years 10 months ago #481 by albertw
Replied by albertw on topic Re: Why are there no green stars?
ok perhaps I'm completely lost but I thought:
A Stars spectra was basically a black body curve.
The presence of H (or Fe, O etc.) in the corona causes absorption lines in that spectum, and that was how we know the elements in the corona.

If it wasnt then wouldnt we see just an emission spectra for the sun at Hydrogen wavelengths?

Have I got the end of the wrong stick here?

Cheers,
~Al

Albert White MSc FRAS
Chairperson, International Dark Sky Association - Irish Section
www.darksky.ie/

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20 years 10 months ago #482 by voyager
Replied by voyager on topic Re: Why are there no green stars?

ok perhaps I'm completely lost but I thought:
A Stars spectra was basically a black body curve.
The presence of H (or Fe, O etc.) in the corona causes absorption lines in that spectum, and that was how we know the elements in the corona.

If it wasnt then wouldnt we see just an emission spectra for the sun at Hydrogen wavelengths?

Have I got the end of the wrong stick here?

Cheers,
~Al


OK, I can never remeber whether we look at emission or absorption spectra from the sun. However the colour is a direct result of the spectrum so it IS affected by the materials in the photosphere. In other words the material in the photosphere directly affects the colour we see a star as. We either see Everything except Hydrogen and co or ONLY Hydrogen and co.

I'm off to do some more research ... post more later.

Bart.

My Home Page - www.bartbusschots.ie

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20 years 10 months ago #483 by voyager
Replied by voyager on topic Re: Why are there no green stars?
Well that didn't take long.

*Bart eats his hat*

OK, the sun IS approximately a black body, the spectrum we get from it is an absorption spectrum. Basically the Hydrogen and Helium in the sun are obsorbing some specific wavelengths, hence preventing us from seeing them but allowing trough the vast majority.

This means that for all intents and purposes the light we get from a star follows the black body curve for an object at what ever temperature the star is at. This curve is quite wide at the top so we always see a large range of wavelengths. We only consider a very small part of the spectrum to be green so I would suggest that we donlt see green stars because any star that is emitting green is also emitting other colours the drown out the green. Pretty much all visible stars radiate strongly in the wavelengths at the middle of the spectrum however cold stars will also radiate strongly towards the red end of the spectrum but weakly towards the violet end of te spectrum while hot stars radiate strongly in both the middle and indigo ends of thes pectrum but not in the red end.

This causes cold stars to appear redish as they contain red, orange and green light, medium stars to appear yellowis as they contain yellow green and blue light and hot stars to appear blueis as they contain green blue and indigo light. However no star appears green becasue green is a very specific colour and no star radiates in just one colour! This would be much easier to explain on a graph but basically the black body curve is too wide to allow any star radiate only green light.

Bart.

My Home Page - www.bartbusschots.ie

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20 years 10 months ago #496 by dave_lillis
Replied by dave_lillis on topic Re: Why are there no green stars?
To say it simply,,,

There are plenty of stars out there pumping out plenty of green light, it just happens that these stars also pump out alot of blue and red light so the star appears white.. .

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Chairman. Shannonside Astronomy Club (Limerick)

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but what a way to go. :)
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20 years 10 months ago #502 by voyager
Replied by voyager on topic Re: Why are there no green stars?

To say it simply,,,

There are plenty of stars out there pumping out plenty of green light, it just happens that these stars also pump out alot of blue and red light so the star appears white.. .


Exactly!

(now why didn't I think o saying it like that!)

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