Joe Flanigan (John Sheppard) and David Hewlett (Rodney McKay) are the only actors to appear in all 100 episodes. Rachel Luttrell (Teyla Emmagan) is the only other regular cast member to stay with the series throughout its entire run.
The shooting set of the Stargate Atlantis base, specifically the balconies where the humans from Earth celebrated their first victory as well as several times depicting the outdoor dining area is the exact same location as the Colson Industries' main office building from Stargate SG-1: Covenant (2004).
Although David Nykl and Paul McGillion were born in the Czech Republic (then Czechoslovakia) and Scotland respectively, both moved to Canada when very young and speak normally with a Canadian accent. The accent used for their characters comes from their parents.
Stargate's ring have 39 glyphs or chevrons. In this TV series as in Stargate SG-1 (1997) and Stargate Universe (2009) is explained that the number of glyphs in a stargate depends of the galaxy where this stargate belongs.
Two of the main cast went on to be main characters in superhero series based on DC comics: David Nykl (Dr. Radek Zelenka) went on to play recurring and sometimes regular character Anatoly Knyaezev on Arrow and Jason Momoa (Ronon Dex) went on to play Arthur Curry/Aquaman in the DCEU. Paul McGillion (Dr. Carson Beckett) also went on to play minor recurring character Earl Cox on The Flash (which exists in the same on-screen universe as Arrow).
The machine is a system to open a wormhole. A wormhole is a hypothetical way of space travel called an Einstein-Rosen Bridge, named after scientists Nathan Rosen and Albert Einstein. According to them, the wormhole should capable to unite two distant points in the universe, altering Space-Time Laws to cross from a point to another in a so brief period of time. The name wormhole was given after a comparative between the universe and an apple, with a worm moving inside. The same concept was used in Contact (1997) as well as Stargate (1994) and their TV series Stargate SG-1 (1997) and Stargate Universe (2009).
The trivia items below may give away important plot points.
In season1, it is stated that approximately 60 Wraith hive ships exist in the Pegasus Galaxy. Over the course of the series, and including a crossover episode with Stargate SG-1 (1997), whether shown on screen or stated by a character, only about 26 hive ships had been destroyed by series' end.
Richard Dean Anderson (Jack O'Neill) and Michael Shanks (Daniel Jackson) are the only two actors to appear in the pilots of both Stargate SG-1 (1997) and "Stargate: Atlantis". Amanda Tapping (Samantha Carter) and Gary Jones (Walter Harriman) are the only actors to appear in the final episodes of both series, as well as the only two actors to appear in the pilot of "Stargate SG-1" and the finale of "Stargate: Atlantis".
A stargate is a ring composed of a fictional superconductive mineral called "naqahdah", marked with 39 glyphs that operates using a combination of 7 glyphs or chrevrons to establish a space route to travel from a point to another. Using mathematical combinatorics, it implies that a single stargate can locate 77,519,922,480 places throughout the galaxy, increased to 45,379,620 if in the combination one of some glyphs can be re-used. Using a 8 glyphs combination for an extragalactic travel, a stargate can locate 2,480,637,519,360 places throughout the universe, increased to 5,352,009,260,481 if one or more glyphs can be re-used.