"Gemini-Titan 8 (GT-8) spacecraft, carrying astronauts Neil A. Armstrong, command pilot, and David R. Scott, pilot, was successfully launched by the National Aeronautics and Space Administration's (NASA) John F. Kennedy Space Center (KSC) at 11:41 a.m. (EST). An attempt will be made to rendezvous and dock the GT-8 spacecraft with Agena Docking Target Vehicle."
"The mission patch shows the whole spectrum of objectives that were hoped to have been accomplished on Gemini 8. The text at the bottom is composed of the zodiacal symbol for Gemini, , and the Roman numeral for eight, VIII. The two stars are Castor and Pollux, which are in the constellation of Gemini, and are refracted through a prism to provide the spectrum. Armstrong and Scott both designed the flight patch."
-Info from Wikipedia: link
NASA ID: KSC-66PC-0038, S66-24465, S66-18616, 104-KSC-66P-138, SPD-MARSH-9141927, S66-23978