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pompanoJ t1_itusinq wrote

Reply to comment by mucaro in Interstellar dust allowed scientists to look at the Milky Way from distant galaxies by OkOrdinary5299

They do not do anything at all like looking at the Milky Way from remote galaxies.

They use the light from remote galaxies and quasars to map the gas and dust in the Milky Way. It is like holding a flashlight behind a piece of paper and trying to figure out what is written on it by looking at how the light dims. Except they use radio waves of various wavelengths. They look at how the light is scattered and absorbed and map the material doing the scattering and absorption.

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mucaro t1_ituta1a wrote

Yes and I understood that. It is the resulting EM signals that I think may not correlate exactly with the position in soacetime with dust and other objects.

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pompanoJ t1_ituvc5u wrote

"I wonder how far back in spacetime the resulting images will be"

Everything they are talking about mapping is inside the Milky Way. The Milky Way is about 100,000 light years across. Most of the stuff they are mapping would be within 50,000 light years, give or take. It is all gravitationally bound, so there is no expansion component. That is how far back in time the images will be.

"But they moved a little bit in the last 20,000 years" isn't all that interesting. I mean, yeah, it all orbits the galactic center. But that is kinda baked into "I am observing things inside the Milky Way."

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