Kammala jumla mai zuwa: A cikin 1920 an yi muhawara tsakanin Harlow Shapley da Heber Curtis (wanda aka fi sani da Harlow Shapley)
Babban muhawara), game da yanayin Milky Way, da kuma yanayin sararin samaniya. Don tallafawa da'awarsa cewa Babban Andromeda Nebula wani galaxy ne na waje, Curtis ya lura da bayyanar layuka masu duhu waɗanda suke kama da gajimare na ƙura a cikin Milky Way, da kuma mahimmancin Doppler.