Rubuta ci gaba don wannan sakin layi - A cikin 1920, Babban Muhawarar
tsakanin Harlow Shapley da Curtis ya faru, game da yanayin Milky Way, nebulae na karkace, da kuma girman duniya. Don tallafawa da'awarsa cewa Babban Andromeda Nebula (M31) wani galaxy ne na waje, Curtis ya kuma lura da bayyanar layuka masu duhu waɗanda suke kama da gajimare na ƙura a cikin galaxy ɗinmu, da kuma canjin Doppler mai mahimmanci. A shekara ta 1922 Ernst Öpik ya gabatar da wani kyakkyawan tsari mai sauƙi na astrophysical don kimanta nesa na M31. Sakamakonsa ya sanya Andromeda Nebula nesa da galaxy a nesa da kimanin 450,000 parsecs, wanda yake game da 1,500,000 ly. Edwin Hubble ya warware muhawara game da ko akwai wasu taurari a 1925 lokacin da ya gano taurari masu canzawa na Cepheid na farko a kan hotuna na astronomical na M31. An yi waɗannan ne ta amfani da na'urar hangen nesa ta Hooker mai tsawon mita 2.5, kuma sun ba da damar ƙayyade nisan Great Andromeda Nebula. Ƙididdigar da ya yi ta nuna cewa wannan ba tarin taurari da iskar gas ba ne a cikin damin taurari, amma wani damin taurari ne dabam da namu, kuma yana da nisa sosai. Wannan ya tabbatar da wanzuwar wasu taurari.