An understanding of the cosmological expansion and Hubble’s work is critical for students studying the birth and evolution of the universe. In order to determine the speeds of the galaxies, Hubble used Vesto Slipher’s work showing that spiral nebulae (now known to be galaxies) have redshifted spectra; he built upon Henrietta Leavitt’s work on Cepheid variables to determine the distances to those galaxies. His graph (Fig. 1) showing that galaxies farther away from us are receding from us faster1 is a large part of the groundwork on which modern cosmology has been built.2–4 

However, in our experiences working with high school students and undergraduate students in introductory astronomy courses, it is not intuitive for many of the students that a graph such as that created by Hubble indicates an expanding universe. Additionally, students often have misconceptions about the big bang theory in which they believe the big...

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