... Arp 230: Two Spirals in One? ... Is this one galaxy or two? ... The slow motion collision took place over about 100 million years and induced a burst of star formation that has begun to subside. The United States at Night . ... The Trifid nebula (M20) is a bright star forming region in Sagittarius, 5000 light years from Earth. In visible light, the interstellar gas cloud is crossed by dark, obscuring dust lanes which roughly divide the glowing emission nebula into three major parts. ...