Timeline of knowledge about 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
- 1990 — Foreground "contamination" data from the COBE spacecraft provides the first all-sky map of the ISM in microwave bands.
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