Watch the entire series here: The Realm of the Galaxies: Astronomy class at William Paterson University: This is part of my complete intro Astronomy class that I taught at Willam Paterson University and CUNY Hunter. If you want to watch all the videos in the correct order, please visit my website at Edwin Hubble discovered the expansion of the Cosmos by seeking the distance to the Andromeda Galaxy. What is the cosmic redshift and how was it found? Supplement the videos with "OpenStax Astronomy" 26: Galaxies 27: Active Galaxies, Quasars, and Supermassive Black Holes 28: The Evolution and Distribution of Galaxies 0:00 Introduction 2:43 Discovery of Expansion by Vesto Slipher 3:40 Hubble Discovers the Distance-Redshift Relation 4:31 Cepheid Variables and the Leavitt Relationship 5:57 Hubble's and Humason's 1929 Velocity Data 8:44 Galaxies show redshift proportional to distance 10:26 Hubble's Law 12:21 Analogy to Doppler Shift 13:16 Redshift Definition 14:05 Redshift is like a Doppler Shift... 16:55 Cosmological Redshifts 19:33 Redshift Distances have their limitations... 22:11 Interpretation as the Expansion of the Cosmos 23:18 The Nature of the Expansion 27:17 Cosmic Expansion; the Universe is Growing 28:10 What is Cosmological Redshift? 31:44 How Does Redshift Measure Expansion? 33:34 Redshift Measures the Change in Size 44:04 Different Ways to Measure Distance 47:45 Apparent size as a function of redshift 49:39 Therefore, the universe is expanding! 52:29 REVIEW QUESTIONS.