1. Trumpler, R.J. (1930) “Absorption of Light in the Galactic System.” Publ. Astr. Soc. Pac., 42: 214.
2. Shapley, H. (1917) “Studies Based on the Colors and Magnitudes in Stellar Clusters, First Part, The General Problem.” Astrophys. J., 45: 130.
3. Curtis, H.D. (1917) “Absorption Effects in Spiral Nebulae.” Proc. Nat. Acad. Sci., USA, 3: 678.
4. Seeley, D., Berendzen, R. (1972) “The development of research in interstellar absorption, c1900-1930.” J. Hist. of Astr., 3: 52.
5. Globular clusters are closely packed agglomerations of old stars, sometimes thousands to a cluster, which are linked to our Milky Way by mutual gravitational attraction and drift in a spherical “halo” about the center of the Galaxy like flies around a picnic table.