The expanding universe: an introduction

An introduction to the physics and mathematics of the expanding universe, using no more than high-school level / undergraduate mathematics. Covered are the basics of scale factor expansion, the dynamics of the expanding universe, various distance concepts and the generalized redshift-luminosity relation, among other topics.
Comment: 107 pages, 33 figures. Extended notes for a lecture held as part of the WE Heraeus Summer School "Astronomy from Four Perspectives: The Dark Universe" at Haus der Astronomie, Heidelberg, on 28 August 2017