How are all of the observed properties of stars (Luminosity,\nMass, Radius, Temperature and Spectral Type) related to one another?\nThis lecture introduces the Herzsprung-Russell Diagram, a plot of \nLuminosity versus Temperature for stars that is our most powerful tool \nfor unlocking the secrets of the stars. \nRecorded 2006 January 17 in 1008 Evans Laboratory on the Columbus campus\nof The Ohio State University.