A Historical Perspec/ve on the Interstellar Medium John Dickey University of Tasmania IAU GA XXVIII -- SpS 12 27 AuGust 2012 Pre-modern Era: late 1800's – 1950: Herschel's lists of liGht and dark nebulae were reobserved and photoGraphed, some were analysed as HII reGions. General obscuraon and reddeninG of distant -1 stars were measured: Av kpc . and dust cloud sizes and numbers were determined. Spectral lines includinG molecular lines were detected from interstellar clouds. Barnard 1903 Ap. J. 17, 77. Barnard 1903 Ap. J. 17, 77. Barnards Loop (Orion) by Drew Sullivan, APOD 2009-02-24 Johannes Hartmann 1904 Ap. J. 19, 268 Detec/on of Ca absorp/on lines with a constant radial velocity very different from the chanGinG velocity of the backGround star, δ Orionis, a binary system. Comstock, G.C. 1904, A.J. 24, 139. Washburn Obs., Univ. Wisconsin Kapteyn, J. C. 1909, Ap. J. 29, 46. Jacobus Kapteyn Groningen Univ. m Kapteyn's result: AV = 0.016 / 10 pc m -1 modern value: AV = 1.8 kpc Shapley, H. 1918 PASP 30, 42. Shapley, H. 1918 PASP 30, 42. Trumpler 1930 PASP 42, 214. Viktor Ambartsumian On the Radiave Equilibrium of a Planetary Nebula 1932 MNRAS 93, 50. late 1930's work: TracinG interstellar clouds throuGh obscuraon – varyinG star density. backGround: Barnard 68 fORS Team VLT APOD 2012-01-12 Ambartsumian, V. Reviews of Modern Physics 30, 944 (1958). NGC 6823 from the CfHT (astronomy picture of the day 2004-10-4) Ap.J. 112, 380 (1950) Equilibrium between ionizaon and recombinaon sets the radius of the ionized reGion around an O star. 1939 Ap. J. 89, 526. from StrÖmgren's memoir 1983 ARAA 21, 1. IC 1396 POSS II composite by Davide De Mar/n APOD 2005-09-08 Dunham 1937 PASP 49, 26. Stellar absorp/on lines 1949 Ap. J. 109, 354. from molecules CH, CH+, and CN compared with Ca H and K lines Note: Adams was following up detec/ons from 1936 by Beals (DAO). 1952, BAIN 11, 459. Early Modern Era: late 1951 – 1977: 21-cm line maps show en/re Milky Way ISM extent and velocity field. Molecular lines show GMC distribu/on. ISM temperatures determined and explained. Galac/c Halo proposed, coronal Gas detected. SNR effects on the ISM studied and incorporated. backGround Crab Nebula Hale 200" telescope David Kaplan van de Hulst, Muller, and Oort 1954 BAIN 12, 117. LonGitude-velocity diagram of the 21- cm line as measured with the Kootwijk dish 1952-53. Spectral line predicted by van de Hulst (1945), detected nearly simultaneously in 1951 by Ewen & Purcell, Muller & Oort,and Pawsey. Oort, Kerr, & Westerhout, 1958 MNRAS 118, 3790. Oort, Kerr, & Westerhout, 1958 MNRAS 118, 3790. Spitzer 1956, Ap. J. 124, 20. Clark, B.G. 1965 Ap. J. 142, 1398. Absorp/on in the 21-cm line spectra taken with a spectral line system on the Owens Valley interferometer. The strikinG difference between the widths of the emission and absorp/on lines shows that the atomic Gas is in two thermal phases with very different temperatures. field, Goldsmith & HabinG 1969, Ap. J. 155, 149. DalGarno & McCray 1972 ARAA 10, 375 Gould & Salpeter 1963, Ap. J. 138, 393. H2 detected by Copernicus satellite (Carruthers 1970 Ap J Len. 161, L81) Parker 1966, Ap. J. 145, 811. Barren, Meeks, & Weinreb 1964, Astron. J. 69, 134. Detec/on of the OH molecule in absorp/on at 1667 MHz usinG an autocorrelaon spectrometer. 1970, Ap. J. 141, L43 1983 HiGhliGhts of Astronomy 6, 681. all sky maps of soo x-rays 130 eV - 188 eV 160 eV - 284 eV Data from the Copernicus orbi/nG uv-observatory. backGround simeis 147 by Nobuhiko Miki Recent Years (1978 – today) themes: Disk-Halo Connec/on (super-shells and chimneys) Magneto-ionic Turbulence Tracers and theory Dust temperatures and PAH emission (IRAS – Herschel) Tiny Scale Structure (VLBA) Star formaon in Ac/on (HST – ALMA) backGround: Herschel's CyG X (Hennemann and Mone) APOD 2012-05-17 Conclusions: • We stand on the shoulders of Giants. • At any Given /me, some of the facts are wronG. • Scien/sts' most important work is some/mes an aside. Tarantula Nebula 30 Dor from the Hubble Space Telescope .