Discrepancy between Sun's radiated max wavelength and it's apparent color

by ramuramu
Tags: blackbody radiation, sun, wavelength, wien law
ramuramu is offline
Apr10-09, 04:39 PM
P: 5
1. The problem statement, all variables and given/known data

By Wien's we can determine that the max wavelength radiated by the sun is around 500 nm.
How does this compare to the apparent color of the sun? Attempt to explain this discrepancy.

2. Relevant equations


3. The attempt at a solution

I said that the sun appears yellow to us (600-630nm) even though lambda max is around
500nm (blue-green). This is using 5.79x10^3 K as a surface temp. At first I thought the discrepancy was due to scattering of photons off molecules/electrons but that would yield a higher apparent frequency, not a lower one. Then, I thought it was simply that the sun appears white, we observe all wavelengths together, not just the max one.

Does this make sense?

Although, if you had a red-hot poker you only observe the lamdba max mainly->red. This makes me think there is something more to the answer. We have been studying blackbody radiation in a sophomore modern physics class.

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Jack21222 is offline
Apr10-09, 04:51 PM
P: 771
Your second thought is correct. If you see the sun as yellow at any time when the sun is high overhead, get your eyes checked. We see the sun as white almost all day, so go off of that assumption. The only time the sun appears yellow is when it is close to the horizon.
ramuramu is offline
Apr10-09, 05:54 PM
P: 5
Thank you very much. I see. So the simple explanation is that we just observe all the wavelengths of visible light->white. What do you think about the red-hot poker example?
Do you think that the sun's radiation is just so much stronger than the poker's, so that's why with the poker we only really observe the lambda max->red?

THANK YOU, again!

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