The Milky Way Galaxy is the most significant for the human race, as it's home to them as well as to possibly many other alien races seen in the show.
Since the Irkens were unaware of Earth's existence, it's conceivable that Irk is not in the Milky Way, though they seemed to at least be aware of the galaxy's existence. The evidence for this is that it's technically a part of the universal map for Irken conquest, with Earth taking the form of a small, yellow paper note taped on the extreme edge of the map. Most likely, it's existence was probably just guessed at, based on long-range scans.
In "Career Day", Dib found out about "The Galactic Equinox Theory" which states that at 5 o'clock on an undetermined day, the galaxies were to be perfectly lined up, which causes all the aliens that are living off their own planets to go through a hideous molt for about a minute. Zim was aware of this and tried to hide the molt but failed horribly; however, since humans are not that observant, his cover was safe but he was fired from MacMeaties for making a mess. It's likely all the Invaders on their assigned planets were also aware of the equinox and were hiding to keep their covers from being blown.
Facts of Doom
- In real life, the Milky Way is a barred spiral galaxy with a diameter between 150,000 and 200,000 light-years. It is estimated to contain 100 to 400 billion stars and more than 100 billion planets, of which it's believed by astronomers that about one million could potentially support life.
- Since most aliens seen in the show are unaware of Earth's existence, it's probable that most are not from the Milky Way and if that's the case, then it's possible they could come from the nearest galaxy, which is the Andromeda Galaxy.
- In "Career Day", Bill told Dib that the galactic equinox would cause the galaxies to line up, though when the event actually occurred, only the planets were shown lining up.
- The Milky Way technically makes an appearance in every episode and comic issue.
- The Almighty Tallest often change the name of the plans for Operation Impending Doom II from "Universal Conquest" to "Galactic Conquest", putting into question whether the planets marked by the Irkens are in just one galaxy or several galaxies.
- Since both the Nhar-Gh'ok and the Slaughtering Rat People are aliens that resemble life on Earth, it could hint at the possibility that their home planets are somewhere in the Milky Way.