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Author Topic: How do all the photons that leave the Sun combine to make white ?  (Read 3714 times)

Offline Fozzie

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The photons which leave the surface of the sun have a range of energy levels which can be split up by a prism forming the familiar rainbow of colors, blue for high energy photons and red for low energy etc. How is it then that the combination of all these colors is just right so that it produces white? It seems rather a coincidence! (OK, I know the sun is officially classed as yellow, but it looks white to me!). Surely if the energy levels of just one group of those photons varied, the sun would change color?







« Last Edit: 09/11/2009 16:14:53 by neilep »


 

Offline Mr. Scientist

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White? White what.. light?
 

Offline Madidus_Scientia

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Actually, the sun is white. It looks yellow during sunset or sunrise due to atmospheric scattering, but if you look at it at midday you will notice it's white.
 

Offline syhprum

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Our eyesight has evolved with the assumption that the light from the sun is white, if it was a dull red or a high temp blue we would still think of it as white.
 

Offline RD

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All colours are not equally represented in sunlight: the sun is currently yellow-green star ...

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Most of the sun's radiation comes to us in the yellow-green part of the visible spectrum.
http://www.nasa.gov/worldbook/sun_worldbook.html
 

Offline lightarrow

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The photons which leave the surface of the sun have a range of energy levels which can be split up by a prism forming the familiar rainbow of colors, blue for high energy photons and red for low energy etc. How is it then that the combination of all these colors is just right so that it produces white? It seems rather a coincidence! (OK, I know the sun is officially classed as yellow, but it looks white to me!). Surely if the energy levels of just one group of those photons varied, the sun would change color?
White is not the colour of a single wavelenght, so it has not a physical meaning, but only perceptive. If you try to define the word "white" you begin to understand something...
 

Offline Soul Surfer

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We evolved under sunlight and colours are essentially differences between the illumination under sunlight.  White is an arbitrary measure of even reflection of all wavelengths and in eyesight varies according to the light source. For example compared with sunlight ordinary tungsten filament light is a reddish orange. If you took colour pictures with old fashioned film cameras you had to compensate for this with filters.  Modern digital colour sensors automatically compensate for this because they are programmed to adjust the colours to match what the human eye would see.
 

Offline lightarrow

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It's not so simple, Ian. We perceive as white even what is not necessarily sun light. Do you know the phenomenon of coloured shadows? The colour white is not only in our retinas, but in our minds too.
 

Offline Soul Surfer

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I agree but From the level of the question I thought that a simple answer would be adequate. 

I am well aware its is possible for us to see a full range of (rather attenuated) colours from objects illuminated with only a relatively narrow (but non zero) spectrum of yellowish light. That is with no red or blue light presence at all.  This is because our perception of colour depends on the difference in reflectivity of objects with our three types of colour sensors in our eyes
 

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