Interstellar matter

Interstellar space is not a perfect vacuum but contains thin wisps of gas and dust that dim and redden light over vast distances. This discovery corrected previous estimates of the Galaxy's size.
 Robert Julius Trumpler United States 1930 Interstellar matter

Interstellar space is not a perfect vacuum but contains thin wisps of gas and dust that dim and redden light over vast distances. This discovery corrected previous estimates of the Galaxy's size.