It’s Earth, the modern day…and in the out there, there is a fight going on. Two vast space-empires duel for survival, locked in hateful combat. Clashes of fleets and individual spaceships are the most common method of conflict; controlling the ultimate “high-ground” of space an almost guaranteed success for any battle on a different field.
Ships of all (reasonable) sizes combat one another, from small fighter sized craft to carriers and battleships the size of skyscrapers. The weapons they commonly use against one another would not be unfamiliar to modern humanity, merely advances on what we use now; lasers, railguns, and nuclear missiles, along with a smattering of more exotic methods of inviting entropy upon an enemy.
For some reason they are fighting one another in or around the Sol system. Perhaps they were drawn here by weird radio signals that they assumed to have been from an enemy’s base. Each empire sends in expeditionary forces to investigate and they lock in combat when they “warp in” on top of one another perhaps.
How “close” do they have to fight to Earth, with the above ships and weapons, to be “noticed”? Would they be observed duking it out around Pluto? Or would they be missed if they were tossing nukes around between Earth and the Moon?
I know random chance is really everything, but discounting that, I’m after the limits of where it is reasonable to place a couple of Type I civilization space-fleets doing their best to end each other somewhere in the solar-system where they will be observed. We have good number of things pointed at space, but they all cover just a very small portion of it, and I’ve only heard of the idea of actively looking for asteroids more than a relatively short distance out. I have no clue how close something that’s actively emitting energy has to get before it is “seen”.
it happens “close" enough that more than one telescope picks it up; it should be an obvious enough event that it couldn’t/wouldn’t be covered up.
They get here by a method of an “effective FTL”, wormholes or some other technique that doesn’t violate reality, but they’ve figured out how to be moderately stealthy about it.
They use technology that is “explainable” (outside wormholes), no hand-waving; if it’s not possible they don’t have it. Their FTL method isn’t well suited for weapons or real-space communications. If it’s reasonable for humans in the next 100 or so years, they probably do have it.
No particular assumptions on their tactical and strategic decisions beyond whatever will take them to the location that they can/will be discovered.
Also; while they may or may not pointing their weapons specifically at earth on occasion, its not about the speed of light; it's about if we would notice them and look back along the trajectory of whatever and see where and what it was coming from.
The general idea is that people witness and know that there is a fight going on out there; not particularly the details, but we should be able to see the “fight” and observe the debris afterward.