他们长途跋涉要横跨整个银河，却在中途燃料耗尽，只好降落到20世纪80年代的约翰内斯堡，靠到处寻找猫食维生。
They trek halfway across the galaxy, run out of gas and end up living off cat food in, of all places, 1980s Johannesburg.
像银河系那样螺旋状的大星系每世纪似乎会出现两到三个。
Large spiral galaxies like the Milky Way seem to have two or three per century.
自上世纪二十年代起，天文学家就尝试着去测量银河系的重量。
Astronomers have attempted to measure the mass of the Milky Way since the 1920s.
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