Today's cosmological edifice is essentially the product of the 20th century
. This account, presented in the Baird Auditorium of the National Museum of
Natural History, begins with the Shapley-Curtis debate of 1920, then descr
ibes some of its historical background (including why cosmology was almost
stillborn with the work of Newton), and finally examines why in 1937 Hubble
erred by an order of magnitude in establishing the Hubble constant.