1. Ambartsumian, V. A. 1958, Solvay Conference Report, Brussels, p. 241
2. Babcock, H.W. 1939, Lick Obs. Bull. 19,(498), 41
3. Bahcall, J. N. 1984, ApJ287, 926
4. Bahcall, N.A., Ostriker, J.P., Perlmutter, S., & Steinhardt, P.J., 1999, Science 284, 1482, astro-ph/9906463
5. Binney, J. & Tremaine, S. 1987, Galactic Dynamics, Princeton, Princeton Univ. Press, p. 638