I
(Latin: "Twins") In astronomy, the constellation lying between Cancer and Taurus; in astrology , the third sign of the zodiac , governing approximately the period May 21–June 21.
It is represented by a set of twins. The twins are most often identified as the mythological Castor and Pollux ( Dioscuri ), but have also been equated with other famous pairs such as Romulus and Remus .
II
Series of 12 two-person spacecraft launched into Earth orbit by the U.S. between 1964 and 1967, following the one-person Mercury program and before the three-person Apollo program.
Designed to test astronauts' ability to maneuver spacecraft manually, the Gemini series helped develop techniques for orbital rendezvous and docking, procedures that were required later in the Apollo Moon-landing missions. It also gave NASA engineers a chance to improve spacecraft environmental control and electrical power systems.