Henrietta Swan Leavitt they became an important part of the evidence that "spiral nebulae" are independent galaxies located far outside of our own Milky Way. Thus, Leavitt's discovery would forever change our picture of the universe, as it prompted Harlow Shapley to move our Sun from the center of the galaxy in the "Great Debate" and Edwin Hubble to move our galaxy from the center of the universe. Leavitt's discovery of a way to accurately measure distances on an inter-galactic scale, paved the way for modern astronomy's understanding of the structure and scale of the universe. The accomplishments of Edwin Hubble, the American
Atlas of Peculiar Galaxies catalogue have been interpreted as galaxy mergers, though Arp refuted the idea, claiming, rather, that apparent associations were prime examples of ejections. He writes in "Seeing Red" (1998): For me, the whole lesson of the "Atlas of Peculiar Galaxies" was that galaxies are generally ejected material. The merger mania seems to be a first guess based on a cursory look at galaxies. [...] The "Atlas of Peculiar Galaxies" contained a very interesting class of galaxies called spirals with companions (smaller galaxies) on the ends of arms. How had they gotten there? Certainly not by accidental collisions or by the beginning