Whakakiia te rerenga e whai ake nei: I te tau 1920 i puta he tautohetohe i waenga i a Harlow Shapley me Heber Curtis (te
Great Debate), e pā ana ki te āhua o te Milky Way, ngā nebulae kakara, me ngā ahu o te ao nui. Hei tautoko i tana kerēme ko te Great Andromeda Nebula he tupuni o waho, i kite a Curtis i te ahua o nga ara pouri e rite ana ki nga kapua puehu i roto i te Milky Way, tae atu ki te nekehanga Doppler nui.