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Why does maps of the CMB not show the Milky way?

steenkh said:
I have looked at some maps of the Cosmic Microwave Background, such as the one in the Wikipedia article on the CMB:
https://en.wikipedia.org/wiki/Cosmic_microwave_background

I wonder why the Milky way is not visible as a smudge across the cosmic equator. Do these microwaves pass right through a galaxy without being absorbed in any way?
Click to expand...
I thought its effect was intentionally removed from the image because it is local and not cosmic. Is that right?
 
That may be true, but how do you remove the effect of the Milky Way from the image? If the microwaves are absorbed, how do you reconstruct them?
 
steenkh said:
That may be true, but how do you remove the effect of the Milky Way from the image? If the microwaves are absorbed, how do you reconstruct them?
Click to expand...
A beam of electromagnetic radiation is not affected by passing through another beam.
 
The CMB has a very specific spectrum because the mechanism of emission and the extreme redshift (among other factors such as interactions en route.) There is loss by absorption but there's also a lot of signal that is not absorbed for any area of sky because of the uniform nature of the signal across the sky.

http://www.ustream.tv/recorded/41418326

Start around the 21:00 mark -- or watch the whole thing.
 
Also, the CMB peak wavelength is long enough (almost a millimeter) that not many things will absorb it. QM effects will only allow most things to absorb specific wavelengths (plasmas and soups being the exception). If it's not absorbed, it will pass through unaffected.
 
GodMark2 said:
Also, the CMB peak wavelength is long enough (almost a millimeter) that not many things will absorb it. QM effects will only allow most things to absorb specific wavelengths (plasmas and soups being the exception). If it's not absorbed, it will pass through unaffected.
Click to expand...
Thank you to all of you who replied.

It was absorption that I was most concerned about, but the point that there is very little that can absorb the CMB is a good point. The other replies are more about foreground radiation that I had not even considered, and I see that a lot of work has been done in eliminating these sources.
 
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