Charles Liu

of a motion as opposed to the red shift of the expansion of the universe or the colors intrinsic to the objects themselves.

The answer to this quandary is spectroscopy.

It is a technique where we divide the colors into component colors.

So instead of just seeing red, you see very red and an orangish red and

orangish, orangish red, orangish, orangish, orangish red, and so on and so on and so on.

Okay.

Yes.

Until you get to that orange.

But what happens is that by dividing all these colors up into little bits, the components of that reddishness that you see from a star are broken up into emission lines, absorption lines, and continuum radiation.

And the patterns of those different lines and continuum are preserved regardless of whether or not you redshift due to velocity or not.

So if something looks red, which you thought was blue, you measure the object using spectroscopy and you take a look to see if the patterns, absorption and emission lines, have been preserved in the red part of the spectrum when you thought it should be in the blue.

If they're preserved, then we know it was because of redshift.

If they're not preserved, then we think, oh, there's something physical going on in the star that made that color change.

Yeah.

Yes, because the cosmic microwave background, as it currently exists today, produces the same wavelength of microwave radiation as dust of a certain composition at a certain temperature.

And so that dust turns out to envelop our Milky Way galaxy at different thicknesses or different densities, depending on which direction you look.

And so if you were unable to get that signal cleared away from the cosmic microwave background, that interference will completely mess up your interpretation.

Yes.

You know what I'm saying?

Excellent point.