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ASTR112 Astrophysics: the Galaxy Prof. John Hearnshaw 2003 semester 1 Room 804, Rutherford Building Department of Physics and Astronomy email: [email protected] Panorama of the Milky Way showing millions of faint stars, star clusters, gaseous nebulae and dark clouds in a great circle around the galactic equator. Galileo in 1610 first used a telescope to resolve the Milky Way into a myriad of faint stars. Prof. John Hearnshaw ASTR112 The Galaxy Lecture 1 ASTR112 The Galaxy Lecture 1 Jupiter, wishing to immortalize his infant Hercules (whose mother was the mortal Alcmene) held him to the breasts of the sleeping goddess Juno. The milk spilt and spurted upwards to form the Milky Way Prof. John Hearnshaw The Origin of the Milky Way by Jacopo Tintoretto c. 1575 ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Historical introduction to the Milky Way: Some key landmarks in galactic research ASTR112 The Galaxy Lecture 1 Herschel’s Galaxy cross-section was based on star counts. Fainter stars, he reasoned, indicated a greater distance to the edge of the star system that comprised the Milky Way. Prof. John Hearnshaw Historical introduction • William Herschel’s Galaxy of 1785 ASTR112 The Galaxy Lecture 1 •Jacobus Kapteyn’s Galaxy, 1922 (Kapteyn’s universe) The Sun is in the centre of Kapteyn’s universe, and the contours show locations of equal star density Prof. John Hearnshaw J. Kapteyn (1851-1922) ASTR112 The Galaxy Lecture 1 Harlow Shapley and the distance to the centre of the Galaxy, 1918 Prof. John Hearnshaw • ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw The globular cluster 47 Tucanae, one of the nearer ones to us. It contains over 105 stars. ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Harlow Shapley and globular clusters ASTR112 The Galaxy Lecture 1 Dust clouds in the Galaxy (E.E.Barnard, M.Wolf), 1913-27 l: Barnard photo of Milky Way centre: Dark cloud Barnard 86 r: Edward Emerson Barnard (1857-1923) Prof. John Hearnshaw • ASTR112 The Galaxy Lecture 1 Robert Trumpler in 1930 compared the distances of star clusters from angular size with those from photometry. He showed space cannot be transparent by the discrepancy found. Prof. John Hearnshaw • Work of Robert Trumpler on interstellar dust absorption, 1930 ASTR112 The Galaxy Lecture 1 Jan Oort (1900-92) Dutch astronomer Prof. John Hearnshaw • Rotation of the Galaxy (Strömberg, 1924; Oort 1926) ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw • Discovery of galactic spiral arms, 1951 Young open star clusters and OB associations near the Sun show parts of three spiral arms, called the Perseus, Orion and Sagittarius arms (from outside inwards). Prof. John Hearnshaw ASTR112 The Galaxy Lecture 1 ASTR112 The Galaxy Lecture 1 • Spectroscopic analysis of gaseous nebulae by left: Orion nebula right: Sir William Huggins (1824-1910) Prof. John Hearnshaw William Huggins, 1864, who showed they are gas clouds of hot low density gas from their emission line spectrum ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw • Discovery of 21-cm radio radiation from cold atomic hydrogen gas clouds in disk and spiral arms of Galaxy, 1951 (21-cm radiation was predicted theoretically in 1944). ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw • Discovery of spiral structure from HI 21-cm map of Galaxy (Oort et al. 1958) • Discovery of interstellar organic molecules, especially in microwave region, from 1963. The molecules include OH, CO, H2O, H2CO and C2H5OH etc. Prof. John Hearnshaw ASTR112 The Galaxy Lecture 1 ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw End of lecture 1