ASTR112 Astrophysics: the Galaxy Prof. John Hearnshaw 2003 semester 1 Room 804, Rutherford Building Department of Physics and Astronomy

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw 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.

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw The Origin of the Milky Way by Jacopo Tintoretto c 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

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 Prof. John Hearnshaw Historical introduction William Herschel’s Galaxy of 1785 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.

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw 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 J. Kapteyn ( )

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Harlow Shapley and the distance to the centre of the Galaxy, 1918

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw The globular cluster 47 Tucanae, one of the nearer ones to us. It contains over 10 5 stars.

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Harlow Shapley and globular clusters

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Dust clouds in the Galaxy (E.E.Barnard, M.Wolf), l: Barnard photo of Milky Way centre: Dark cloud Barnard 86 r: Edward Emerson Barnard ( )

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Work of Robert Trumpler on interstellar dust absorption, 1930 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.

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Rotation of the Galaxy (Strömberg, 1924; Oort 1926) Jan Oort ( ) Dutch astronomer

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Discovery of galactic spiral arms, 1951

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw 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).

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Spectroscopic analysis of gaseous nebulae by William Huggins, 1864, who showed they are gas clouds of hot low density gas from their emission line spectrum left: Orion nebula right: Sir William Huggins ( )

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)

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw Discovery of interstellar organic molecules, especially in microwave region, from The molecules include OH, CO, H 2 O, H 2 CO and C 2 H 5 OH etc.

ASTR112 The Galaxy Lecture 1 Prof. John Hearnshaw End of lecture 1