Timeline of the interstellar medium and intergalactic medium
- 1848 - Lord Rosse studies M1 and names it the Crab Nebula
- 1864 - William Huggins studies the spectrum of the Orion Nebula and shows that it is a cloud of gas
- 1927 - Ira Bowen explains unidentified spectral lines from space as forbidden transition lines
- 1930 - Robert Trumpler discovers absorption by interstellar dust by comparing the angular sizes and brightnesses of globular clusters
- 1944 - Hendrik van de Hulst predicts the 21 cm hyperfine line of neutral interstellar hydrogen
- 1951 - H.I. Ewen and Edward Purcell observe the 21 cm hyperfine line of neutral interstellar hydrogen
- 1956 - Lyman Spitzer predicts coronal gas around the Milky Way
- 1965 - James Gunn and Bruce Peterson use observations of the relatively low absorption of the blue component of the Lyman-alpha line from 3C9 to strongly constrain the density and ionization state of the intergalactic medium
- 1969 - Lewis Snyder, David Buhl, Ben Zuckerman, and Patrick Palmer find interstellar formaldehyde
- 1970 - Arno Penzias and Robert Wilson find interstellar carbon monoxide
- 1970 - George Carruthers observes molecular hydrogen in space
- 1977 - Christopher McKee and Jeremiah Ostriker propose a three component theory of the interstellar medium