What kind of observation can be made to verify the existence of cosmic dust (space dust)?
As I understand it: as the light from a known source (measured and steady luminocity and known wavelength) behind the dust passes through the dust, this light gets scattered. The light that then reaches the observer is different (color and length). Record these differences and you can determine the dust's molecular make-up and density.
Simply looking up at the milky way at night in a dark area will show you dust, as it blocks light from the rest of the galaxy from reaching us, creating dark dust lanes.
If you take the spectrum of a star and that light passes through dust between the star and us, it will show up in the spectrum as absorption and emission lines.
Unlike interstellar gas, cosmic dust does not have absorption or emission lines. It causes scattering and extinction of light emitted by more distant sources making it a real PITA to astrophysicists.
Go to a very, very dark place (hard to find, you have to make a special effort and go far from highways, cities, and towns on a clear moonless night), wait for your eyes to fully dark-adapt (might take half an hour or more), and look up - you can see dust within our solar system as zodiacal light and gegenschein.
Ahh, I figured so.
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