Rubuta ci gaba don wannan sakin layi - Kafin a fahimci cewa tauraron dan adam na sararin samaniya ya wanzu a waje da Milky Way galaxy, ana kiran su da "nebulae na sararin samaniya". Tambayar ko irin waɗannan abubuwa sun kasance galaxies masu zaman kansu ne daga Milky Way, ko kuma wani nau'i na nebula da ke cikin galaxy namu, shine batun Babban Muhawarar
na 1920, tsakanin Heber Curtis na Lick Observatory da Harlow Shapley na Mt. Gidan kallo na Wilson. Farawa a 1923, Edwin Hubble ya lura da masu canjin Cepheid a cikin wasu nebulae masu juyawa, gami da abin da ake kira "Andromeda Nebula", yana tabbatar da cewa, a zahiri, dukkanin taurari ne a waje da namu. Maganar "ƙuƙwalwar ƙuƙwalwa" tun lokacin da aka yi amfani da shi.