NATS 1745 Lecture Notes - Lecture 19: Gravitational Lens, Edwin Hubble, Galactic Center
23 Mar 2016
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1923: edwin hubble observed cepheid in andromeda galaxy. 1929: hubble discovers expanding universe: more distant galaxies have higher redhifts using hubble"s law to get distances to galaxies further implications of hubble"s law: the necessity of a big bang; age of universe. Hubble"s classification scheme for galaxies: spiral, elliptical, irregular using supernovae as standard candles. 1998: accidental discovery of the accelerating universe: dark energy discovery of dark matter. Shapley established (slightly incorrect) scale for our galaxy + off-center location for sun. Galaxy: 100kpc (kiloparsec 1000 parsec; 1p=3 light years) The galaxy was so large that shapley thought spiral nebulae" were part of our galaxy. Neither won the debate it became an extended discussion over many years, involving many astronomers. Key turning point: discovery of a cepheid variable star in the andromeda galaxy 1923: outline the observation + the scientific method that hubble would follow to determine distance to andromeda.
