Rubuta ci gaba don wannan sakin layi - A daidai wannan yanayin da ake amfani da shi a cikin ilimin sararin samaniya, wata muhawara mai tsawo game da tsarin sararin samaniya yana zuwa ga ƙarshe. Harlow Shapley, masanin astronomer na Mount Wilson, ya ba da shawarar samfurin sararin samaniya wanda ya kunshi tsarin tauraron Milky Way kawai; yayin da Heber D. Curtis ya yi jayayya da ra'ayin cewa nebulae masu juyawa sune tsarin tauraron kansu a matsayin tsibirin duniya. Wannan bambancin ra'ayoyin ya zo ne a matsayin babban taron da aka yi a Babban Tattaunawa.
a ranar 26 ga Afrilu 1920 a taron Cibiyar Kimiyya ta Kasa ta Amurka a Washington, DC An warware muhawarar lokacin da Edwin Hubble ya gano Cepheid Variables a cikin Galaxy Andromeda a cikin 1923 da 1924. Nesawarsu ta kafa nebulae mai juzu'i fiye da gefen Milky Way..