Praxyon is a planet in the Milky Way galaxy where the Solar observation outpost is located. Ba'al used this outpost to travel back in time and stop the Stargate Program from ever existing.
History
In an alternate timeline after Qetesh betrayed and killed Ba'al, she set a course for the planet to figure out how Ba'al had known all of the things he had. Before she arrived Colonel Cameron Mitchell, Colonel Samantha Carter, Dr. Daniel Jackson, Teal'c, and several Jaffa gated there through the second Earth Stargate that the Russians had found after persuading Teal'c to help them. Once on the planet Carter discovered how Ba'al had traveled through time and used it to try and find a good enough solar flare to use. In the process Qetesh had arrived in orbit of the planet and began to ring down Jaffa. While holding off the Jaffa, Jackson was the first to be shot and killed. Carter discovered a flare that could send them back to 1929, 10 years before Ba'al killed the crew of the Achilles and sunk the Stargate. As she finished dialing the gate she was also shot and killed. When the gate opened up Mitchell quickly ran through. As he left Teal'c was overcome by the Jaffa and shot and Qetesh came down using the rings. Using his last moments Teal'c drops a grenade out of his hand, killing all of them. As Mitchell fixed the timeline Praxyon is most likely currently abandoned. (Stargate: Continuum)
Praxyon was later discovered by SG-14 and the installation was used by SG-1 to go back in time to ancient Egypt to prevent rogue Tok'ra from changing the timeline. (Stargate SG-1: Moebius Squared)