Complex sentence: As they slowly gain Schirra put Gemini 6A's computer in charge of the rendezvous and then at 5 hours and 4 minutes he saw a bright star that he thought was Sirius, but was in fact Gemini 7.
Split into simpler sentences: As they slowly gained, Schirra put Gemini 6A's computer in charge of the rendezvous. At 5 hours and 4 minutes he saw a bright star that he thought was Sirius, but this was in fact Gemini 7.