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 similar features described in the Arp catalog. Messier 32 (Arp 168), a dwarf galaxy interacting with the Andromeda Galaxy, is included in this category (although the "diffuse counter-tail" is very difficult to see in Arp's photograph). This is another category containing galaxies with tidal tails produced by gravitational interactions. These tidal tails are narrower and better defined than the tidal tails in objects 167-172. This category contains a mixture of different types of objects. Like the galaxies with diffuse filaments or galaxies with counter-tails, some of the galaxies in this category have been involved in interactions, and the filaments are