It's about time to stop referring to Stargate Atlantis as a spin-off of Stargate SG-1. Though the two shows share the same mythology, Atlantis has been running for four seasons now, which has proved that it can be successful as its own show.
Sci-Fi Channel apparently has no plans of letting it go away, given that it has renewed the show for a fifth season, as reported by Variety. The genre-specific cable channel has ordered 20 more new episodes of the sci-fi show following an average of 1.8 million viewers, half a million more than the Sci-Fi Channel's average.
In Atlantis, a group of scientists and military personnel investigate the secrets of the famed lost city and find that it was created by an advanced race. However, Atlantis isn't 20,000 leagues under the sea--it has been discovered light-years away in another galaxy.
Stargate SG-1 ran for 10 years on both Showtime (seasons 1-5) and Sci-Fi (seasons 6-10). Though Atlantis is a spin-off of SG-1, the latter is itself based on the 1994 movie Stargate.
Atlantis may be locked up, but the future of another Sci-Fi original series still hangs in the balance. Flash Gordon, a new take on the popular comic-book and film franchise, is still waiting on a decision for renewal. Sci-Fi vice president of original programming Mark Stern told Variety that the network "has made no decision yet on whether to renew" the freshman series.
For more on Stargate Atlantis and Flash Gordon, check out TV.com's visit to both sets, as well as other Sci-Fi Channel shows, including Eureka and Battlestar Galactica.