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Why do other white stars still appear to be white seen from Earth

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#1 Yourjones

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Posted 17 January 2020 - 09:45 AM

Hello

 

Our sun is a spectral type G (yellow) star, but seen in space, it is white. I understand lots of its wave lengths have been scattered by Earth's atmosphere, so it does not seem white from Earth.

 

The question is, if this "scattering" happens to the sun's light, why are we still seeing other white star white in colour at night? In other words, why do many other white stars like our sun not appear yellow, but still white?

 

Excuse me if this question hardly makes sense. 

 

Thanks



#2 sharkmelley

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Posted 17 January 2020 - 10:39 AM

The sun appears white, at least when it's high enough above the horizon.  It's never been clear to me why type G stars are referred to as "yellow".

 

Mark


Edited by sharkmelley, 17 January 2020 - 10:42 AM.

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#3 mashirts

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Posted 17 January 2020 - 11:06 AM

Keep in mind there is no such thing as a "white" anything. White is a perception of when the entire spectrum of light from purple to deep red is roughly balanced in an objects emission or reflection

#4 bitnick

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Posted 17 January 2020 - 11:38 AM

The sun appears white, at least when it's high enough above the horizon.  It's never been clear to me why type G stars are referred to as "yellow".

 

Mark

Does its light look yellow compared to the blue, scattered light from the rest of the sky? So when a "ray" of sunlight lights up something that is otherwise lit by ambient light, it looks more yellow/less blue?



#5 sharkmelley

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Posted 17 January 2020 - 04:17 PM

Does its light look yellow compared to the blue, scattered light from the rest of the sky? So when a "ray" of sunlight lights up something that is otherwise lit by ambient light, it looks more yellow/less blue?

I simply don't think it looks yellow.  Late morning, when I photograph a colour chart with the "Daylight" white balance setting on my camera, the white patch appears white and the grey patches appear grey, not yellowish white and not yellowish grey. 

 

That's what I mean when I say the sun appears white.  For astrophotography I also use the "Daylight" white balance and sure enough G2V stars come out fairly close to white.

 

Mark


Edited by sharkmelley, 17 January 2020 - 04:19 PM.


#6 Lard Greystoke

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Posted 17 January 2020 - 09:02 PM

A star will only appear tinted at either the red or blue end of the spectrum.  If it peaks at the middle of the spectrum, i.e. yellow or green, there is still a strong contribution of all wavelengths balancing out the general impression to "white".

 

The sun appears white unless affected by the atmosphere.


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#7 llanitedave

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Posted 19 January 2020 - 01:57 AM

How it "looks" is a poor guide for determining its color spectrum.  The detectors in our eyes will saturate at high intensities, so they won't be able to discern red from green from blue if all three cone types are saturated.


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