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Timeline of knowledge about the interstellar and intergalactic medium
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<p><a href="/facts/Timeline/CrrakQ6K">Timeline</a> of knowledge about the <a href="/facts/Interstellar_medium/mokU0WEz">interstellar medium</a> and <a href="/facts/Outer_space/R3LRKyFs">intergalactic medium</a>: </p> <ul><li>1848 — <a href="/facts/William_Parsons,_3rd_Earl_of_Rosse/bPQ37rMF">Lord Rosse</a> studies <a href="/facts/Messier_object/YKz2MxzQ">M1</a> and names it the <a href="/facts/Crab_Nebula/HmAndxQX">Crab Nebula</a>. The telescope is much larger than the small refactors typical of this period and it also reveals the spiral nature of M51.</li> <li>1864 — <a href="/facts/William_Huggins/UVPpNGvt">William Huggins</a> studies the <a href="/facts/Optical_spectrum/frPBh8o5">spectrum</a> of the <a href="/facts/Orion_Nebula/6VWbcqzL">Orion Nebula</a> and shows that it is a cloud of gas</li> <li>1904 — Interstellar calcium detected on spectrograph at Potsdam</li> <li>1909 — Slipher confirms Kapteyn's theory of interstellar gas</li> <li>1912 — Slipher confirms interstellar dust</li> <li>1927 — <a href="/facts/Ira_Sprague_Bowen/U2U6zkWz">Ira Bowen</a> explains unidentified <a href="/facts/Spectral_line/HuI4Bj5f">spectral lines</a> from space as <a href="/facts/Forbidden_line/UeungKv0">forbidden transition lines</a></li> <li>1930 — <a href="/facts/Robert_Julius_Trumpler/akR1f6lp">Robert Trumpler</a> discovers absorption by <a href="/facts/Interstellar_dust/Uy6hlL29">interstellar dust</a> by comparing the angular sizes and brightnesses of <a href="/facts/Globular_cluster/FL0EERJU">globular clusters</a></li> <li>1944 — <a href="/facts/Hendrik_C._van_de_Hulst/CKc332Up">Hendrik van de Hulst</a> predicts the <a href="/facts/21_cm_line/fQaWCT2t">21 cm hyperfine line</a> of neutral interstellar <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a></li> <li>1951 — Harold I. Ewen and <a href="/facts/Edward_Mills_Purcell/V9UC5ygc">Edward Purcell</a> observe the 21 cm <a href="/facts/Hyperfine/aqj0dMut">hyperfine</a> line of neutral interstellar hydrogen</li> <li>1956 — <a href="/facts/Lyman_Spitzer/0pd1ge9R">Lyman Spitzer</a> predicts <a href="/facts/Coronal_cloud/8zAB9mcD">coronal gas</a> around the <a href="/facts/Milky_Way/ulF6lccN">Milky Way</a></li> <li>1965 — <a href="/facts/James_Gunn_(astronomer)/BgQ3khwn">James Gunn</a> and <a href="/facts/Bruce_Peterson/DUal7hTa">Bruce Peterson</a> use observations of the relatively low absorption of the blue component of the <a href="/facts/Lyman-alpha_line/R5xVnKKW">Lyman-alpha line</a> from 3C9 to strongly constrain the density and ionization state of the intergalactic medium</li> <li>1969 — Lewis Snyder, David Buhl, <a href="/facts/Benjamin_Zuckerman/JEd5t9KE">Ben Zuckerman</a>, and Patrick Palmer find <a href="/facts/Interstellar_formaldehyde/hVrTp7E0">interstellar formaldehyde</a></li> <li>1970 — <a href="/facts/Arno_Allan_Penzias/MEautAvP">Arno Penzias</a> and <a href="/facts/Robert_Woodrow_Wilson/CsmuvVqa">Robert Wilson</a> find interstellar <a href="/facts/Carbon_monoxide/CKuLtEMJ">carbon monoxide</a></li> <li>1970 — <a href="/facts/George_Robert_Carruthers/sXu9m57J">George Carruthers</a> observes <a href="/facts/Molecular_hydrogen/BoYHjl0J">molecular hydrogen</a> in space</li> <li>1977 — <a href="/facts/Christopher_McKee/P0EQPlmU">Christopher McKee</a> and <a href="/facts/Jeremiah_P._Ostriker/JH74n2JC">Jeremiah Ostriker</a> propose a three component theory of the interstellar medium</li> <li>1990 — Foreground "contamination" data from the <a href="/facts/Cosmic_Background_Explorer/U3QfJ3Al">COBE</a> spacecraft provides the first all-sky map of the ISM in <a href="/facts/Microwave/HmVSN31Y">microwave</a> bands.</li></ul>