Galactic nebulas are masses of diffuse material within our galaxy . 银河星云是我们星系中的一团团弥散物。
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Some celestial bodies similar to galactic nebulas but without any luminosity sometimes reveal their presence as dark patches obscuring the light of stars beyond them . 某些与银河星云相似但不发光的天体，有时看来象块黑色补丁，遮住了周围的星光。
