"This planet is dying, and it's probably our fault."
— Maj. Samantha Carter
SG-1 travels to K'Tau, a world protected by the Asgard, but inadvertently doom its people when their wormhole introduces a superheavy element to the planet's sun.
"Red Sky" provides examples of the following tropes:
- Alien Non-Interference Clause: The Asgard maintain that they cannot overtly interfere to fix K'Tau's sun without violating their Protected Planets treaty with the Goa'uld.
- Ambiguous Ending: The ending of the episode leaves it ambiguous as to whether Carter's plan worked or the Asgard decided to step in after all after the sun suddenly returns to normal.Daniel: We'll never really know for sure, will we?
- Artistic License – Chemistry: While superheavy elements have been synthesized for many decades using particle accelerators, the elements synthesized have an incredibly short half-life, meaning they exist for time periods between a few milliseconds to a few minutes. They also have only been synthesized in quantities on the atomic scale, though we never actually see the element so it's impossible to gauge what size it was (the casing does seem to indicate it was much larger than that).
- Call-Back: O'Neill, Carter and Daniel are transported to a kind of underground cavern with a holographic representation of Freyr, similar to the Hall of Thor's Might.
- Crystal Dragon Jesus: The people of K'Tau worship Freyr, but their religious observances are done in a style very similar to that of a Christian Mass.
- Ditto Aliens: Lampshaded with the Asgard; after O'Neill is summoned before the council he begins to say that they all look the same, before realizing that it might be considered something of a faux pas, which it definitely is considering what the Asgard are.
- Failsafe Failure: Carter guiltily admits that she deliberately bypassed the failsafes in the gate system in order to get a lock on the planet.
- Loophole Abuse: O'Neill suspects that the Asgard exploited this in order to fix the sun without tipping off the Goa'uld.
- Nice Job Breaking It, Hero: The team accidentally doom the people of K'Tau when they somehow manage to dump plutonium into the sun as their wormhole passes through it, causing it to shift towards the red spectrum of light. Even worse, it turns out that the gate system actually has inbuilt security features to prevent such a thing from occurring, but Earth's dialing program bypasses these in order to reach otherwise inaccessible planets.
- "Not So Different" Remark: O'Neill points out that although the Asgard might be benevolent compared with the Goa'uld, they're still posing as gods to people who don't know any better.
- Screw You, Elves!: O'Neill gives the Asgard a speech to this effect when they refuse to intervene. It doesn't go over well.
- Signs of the End Times: The townspeople interpret the arrival of the team, followed by the sudden change in the sun, as a sign that Ragnarök is approaching.
- Space Elves: Invoked, as the locals insist on referring to the team as "elves".
- Star Killing: The team manage to accidentally poison a sun, though it gets fixed by the end of the episode.
- Time Skip: Three weeks pass after Carter comes up with her plan to send a rocket to the sun, during which time the situation on K'Tau grows ever more dire.
