Qoraal sii wata faqradan - Iyadoo la raacayo qaabkan firfircoon ee cilmiga caalamku, dood dheer oo ku saabsan qaab dhismeedka caalamka ayaa ku soo dhowaanaysay heerkeedii ugu sarreeyay. Cilmi -baaraha Mount Wilson Harlow Shapley wuxuu u ololeeyey qaabka caalamka oo ka kooban nidaamka xiddigaha ee Milky Way oo keliya; halka Heber D. Curtis uu ku dooday fikradda ah in nebula spiral ay yihiin nidaamyo xiddig oo iyaga u gaar ah sida caalamka jasiiradda. Khilaafka fikradaha ayaa gaaray meeshii ugu sarraysay markii la abaabulay Dooddii Weyneyd
26-kii Abriil 1920 shirkii Akadeemiyadda Qaranka ee Sayniska ee Mareykanka ee Washington, DC Dooda ayaa la xaliyay markii Edwin Hubble uu ogaaday Cepheid Variables ee Galaxy Andromeda 1923 iyo 1924. Meelaha fog ee ay ku yaalliin waxay samaysteen nebula spiral oo aad uga fog xadka galaxyada Milky Way.