Ku dhammee weedhan soo socota: Intii uu socday doodda dheerayd ee ku saabsan qaab dhismeedka caalamka, waxaa la gaaray xilli la isku raacsan yahay. 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 wuxuu gaaray heer sare markii la abaabulay Golaha Shacabka.
Dood weyn oo ka dhacday 26-kii Abriil 1920 shirkii Akadeemiyadda Qaranka ee Sayniska ee Mareykanka ee Washington, DC. Doodda ayaa la xaliyay markii Edwin Hubble uu ogaaday Cepheid Variables ee Andromeda Galaxy 1923 iyo 1924. Meelaha fog ee ay ku yaalliin waxay samaysteen nebula spiral oo aad uga fog xadka galaxyada Milky Way.