1. Sullivan, 160.
2. Frank D. Drake, “Methods of Communication,” in Ponnamperuma and Cameron, editors, 139.
3. Sagan, “The Quest for Intelligent Life;” Sagan, Other Worlds, 21.
4. Sagan, The Cosmic Connection, 217; Tarter, in Dick, editor, Many Worlds, 147.
5. McDonough, 228; Baird, 194.