Re: [Phys-l] sun's true color

["LaMontagne, Bob" <RLAMONT@providence.edu>]

Now if one of my students gave this response on an exam I would award 4 out of 10 points. There is a lot of information, but none of it answers the question (What is the color of the Sun?).
 
:-)
 
Bob at PC

________________________________

From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of Joshua Skootsky
Sent: Sun 8/24/2008 10:45 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] sun's true color



(http://upload.wikimedia.org/wikipedia/commons/a/a1/Blackbody-lg.png)

The sun is basically a black body. The energy of the fusion going on in its
core heats the successive layers of increasingly rarefied gas by each layer
(Suns... are like onions) absorbing and releasing heat in the form of
electromagnetic radiation. This gives it a fairly even distribution of
wavelengths in the visible spectrum, a bit heavier around the reds and
yellows than among the blues, that correlates to a black body of its
temperature near the surface.

Note that we, as humans, are much more sensitive to yellows (chartreuse has
the best visibility) than we are to blues. Furthermore, the higher-energy,
shorter frequency (i.e. blue) electromagnetic radiation is more prone to
Rayleigh scattering. This "steals" some of the blue in the sun's light, and
reflects it in a random direction, sometimes back down to us from a point
apparently in the sky. This same process is why the ocean sometimes appears
blue.

On a final note, the sun has always seemed really bright, much too bright
for me to say anything certain about the apparent color to our deceitful
eyes.

On Sun, Aug 24, 2008 at 6:21 PM, Anthony Lapinski
<Anthony_Lapinski@pds.org>wrote:

> Does anyone know the actual color of the Sun? The Sun certainly appears
> yellowish, and then Wein's Law can be used to calculate its surface
> temperature (about 6000 °C). Textbooks confirm this result.
>
> However, I read an article in Astronomy magazine that the Sun is actually
> pure white. Our daytime sky is blue since our atmosphere scatters blue
> light the most. This leaves sunlight with less blue and hence a yellowish
> tint. The article said the color of snow closely matches the Sun's actual
> color because snow reflects the sky's blueness as well as sunlight.
>
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