From The Stargate Omnipedia
Planet where the latest incarnation of the Milky Way Galaxy Alpha Site
is based. The world is 640 light years from Earth
. This Alpha Site has been installed in the side of a mountain to help stave off attack.
HOME TO - Humans
FIRST APPEARED - Covenant
Covenant - Colonel Carter and Alec Colson arrive on P4X-650 to take a ride in the ship that Colson helped design, the F-302.
Endgame - When Teal'c discovers he is unable to dial Earth, he follows protocol and transfers his flag to the Alpha Site.
Gemini - To prevent her from gaining access to Earth, Teal'c and Colonel Carter take Carter Replicator to the Alpha Site on P4X-650.