If
Map 13 contains the realm of the galaxies, then this one encompasses the realm of globular clusters. Our Milky Way contains roughly 200 globular clusters, and a third of them can be found in just 3 of the 88 constellations: Scorpius, Sagittarius, and Ophiuchus. (Ophiuchus occupies a large part of
Map 15. Find Scorpius and Sagittarius on
Map 20.) But this region contains more than just globulars.
Because the Milky Way passes through Sagitta, Aquila, Scutum, Serpens, and part of Ophiuchus, open clusters and nebulae abound here. You won't find many galaxies, however. The reason is the composition of the Milky Way itself. In addition to stars, immense, diffuse gas clouds and dust permeate our galaxy's spiral arms (which we see at night as the Milky Way). This material blocks out light from more distant stars and galaxies. The drop-off in numbers of observable galaxies is so extreme that early 20th-century astronomers referred to this area as the Zone of Avoidance.
