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”.

Some assumptions;

  1. 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.

  2. 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.

  3. 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.

  4. No particular assumptions on their tactical and strategic decisions beyond whatever will take them to the location that they can/will be discovered.

  5. 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.

  • $\begingroup$ Another direction to think about this from: if you're a star traveler "warping" into another system, how do you stop? Are you dropping out of "hyper-space" or decelerating from "lightspeed?" The means of travel will likely have some input into where these two fleets meet up. $\endgroup$ – Lumberjack Jun 10 '16 at 18:14
  • $\begingroup$ Realistically this is a valid concern, but ftl is sort of being hand-waved in this scenario. The idea is that there are things out there using advanced-earth-type technology to swat at each other and their detection range/issues with detection of THAT event, not the ftl drive detection $\endgroup$ – Marky Jun 10 '16 at 18:20
  • $\begingroup$ A proper answer to this question will involve piecing together the following concepts: 1) That the naked eye can see objects down to magnitude 6 or 7, amateur telescopes to 10, really big telescopes to 25. 2) How magnitude and energy compare 3) How distance affects apparent magnitude 4) The energy output (and thus magnitude) of various weapon types. Alas, I have been unable to locate all of this information. Even with all that, you only answer whether the event is observable- you still have to be lucky enough to be looking in the right direction at the right time. $\endgroup$ – cobaltduck Jun 10 '16 at 18:25
  • $\begingroup$ Does "debris" need to be "visible" or would it be enough for mankind to be able to detect the battlefield? I'm thinking radiation or a massive bombardment of neutrinos or something along those lines. $\endgroup$ – Lumberjack Jun 10 '16 at 18:26
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    $\begingroup$ @Lumberjack that's an interesting idea, as an appearance of a radiation filled field/area that wasn't there before would indicate something happened, but even then it might not be obvious what it was from $\endgroup$ – Marky Jun 10 '16 at 18:51

10 Answers 10


They will easily be detected, IF we know where to look. The heat output of a space ship can be easily detected, especially if they are maneuvering using any type of rocket or are using radiators to dump heat produced from weapon firing.

Here is a portion of a discussion about space detection (https://groups.google.com/forum/#!topic/rec.arts.sf.science/-E6r2F8rgnQ%5B151-175%5D)

As for detection range, such a system could spot a single Space Shuttle attitude control thruster firing at a range of fifteen million kilometers. Light up the whole package, main engines and SRBs, and the detection range jumps to twenty billion kilometers.

He is describing using a 2 meter IR telescope, similar to many on Earth. Pluto is well within 20 billion KM from Earth, so assuming we knew to point a 2 meter IR telescope at Pluto, we could detect the heat from all those ships maneuvering and venting (assuming they have to do that).

If they are cooking off nukes we could also detect the gamma rays and x-rays. We have lots of sensors and telescopes set up to detect and track these things, so that will probably be the biggest giveaway of a battle. Powerful visible light telescopes could probably catch explosions as well, though perhaps not as far away as Pluto (maybe the Hubble, which has 10 times the resolution of ground based visible light telescopes).

So the main problem is knowing where to look at all. Radio telescopes are not omnidirectional so radio transmissions and energy broadcasts won't just be picked up automatically. So you must either have the battle occur close enough to earth that we can see it with the naked eye to clue us in (which probably means lunar orbit or closer) or it will have to happen "co-incidentally" were we have a telescope pointed. So chose a place we often observe, like Jupiter.

I doubt lasers and such could be detected around pluto, as they would have to be fired directly at us and be EXTREMELY powerful.

As for seeing the ships themselves out by Pluto, no way unless they are simply MASSIVE. The Hubble has a 0.1 arcsecond of resolution, IIRC, and can barely observe Charon (600 km wide). 0.1 arcsecond is 72 km at 1 AU, and Pluto is 30-50 AU away from Earth, so do the math. Your only hope is that New Horizons happens to be passing by and we can task it to take a look, though I think receiving the images would take quite a while.

  • $\begingroup$ If they're throwing nukes around, good luck getting anything back from New Horizons! Expect data loss due to noise and other interference. $\endgroup$ – Thebluefish Jun 10 '16 at 21:17
  • $\begingroup$ I've been trying to work out just how far away a nuke has to be before we can't see it in the night sky with the naked eye but I'm stumped. I think it will have to be pretty close though, within lunar orbit. But if the antimatter or fusion containment system fails on a ship, THAT might be a big bang. I'm hoping I can come up with a nice equation of energy released equals distance from earth for a point of light as bright as Polaris (The Pole Star) in the sky. $\endgroup$ – Jason K Jun 14 '16 at 17:00

I would go for a No! for that question, because your premises are pretty unlikely.

But as said countless times before: space is vast. Only if your combatants are using a technology that will make them appear within each others weapon range they will start shooting at each other (or, if they are good scouts, break up contact with the enemy and run away to report enemy contact).

I remember only a few sci-fi technologies that will make ftl-ships appear at choke-points - if you just warp in the general direction of your target sun it would be possible for the two factions to appear at the same second at the most opposite places possible without ever noticing each other. Only gate jumps would lead to a shared place of appearance, or something that joints on some Lagrangian points (like the node drive from Sword Of The Stars).

Why do I write down all of this? Because except for the ftl - techniques mentioned above there will be no battle at all. Even when they are able to detect each other appearing (well, its more likely that these who appear first will notice these who appear last but not the other way round), it would be plain dumb to start a battle with someone you need to approach for a day or even longer in a way that its highly notable by your enemy to get even at maximum weapons firing range. Just write down a contact report and get the hell out of there. After all you do not send out an Aircraft Carrier to scout a remote island but deploy a plane that will run for its life if enemies had been spotted. After the contact report had been made, more decisions will be made...

So they will appear, check their sensors and make their way towards that strange source of strange radio noise. At a given point it will become clear that this is caused by "puny humans", so both of them will leave without even knowing the other side is around. Maybe. Or they notice the other side is here too and start thinking that they try to ally with these puny humans. in that case... well, everyone on earth would notice if they are going do some preventative striking.

Back to topic - so beyond all strategic, operational and tactical questions... when one thing did led to another and two groups actually start firing at each other... that would be an event that takes what? Ten minutes? A sudden radio burst from the general direction of Aquarius? Well, we do have them already. So at this point I would join the general opinion that states that you need to look at the right direction at the perfect moment - all that is so far away that its already over when signals arriving here will be impossible to get tracked down.

Its like you are sitting in your room, hearing a firework out there (if you hear it after all) and go outside, but sadly its all over already. If it was pretty close to you, you might spot a flash of light, maybe see the guys who did fire it after all, smell the powder. If it was some kilometers away you come out and notice... nothing. When you start running circles you may find the empty batteries somewhere (good luck with that). And not try to find a firework-battery in a neighborhood that has a diameter of a million kilometer.

If you can see fusion fire lighting up in high earth orbit and your satellite receiver stops receiving and litters up earth would notice, but as soon as its done in a distance of a light minute, just a bunch of hard to track signals will be received. If someone looks there after the action and can resolve junks of spaceships with whatever he is looking there its likely too to reconstruct what did happen, but in most cases... well, what was that? After all, dead spaceships will look like another uninteresting asteroid... at least as long as no probe tries to land on it.

So if you want them to do a spectacle have them brawl in high to low earth orbit. Just hide one side at the dark side of the moon while the others are approaching and place a officer in command with a nervous (or happy) trigger finger. Everything else? Incredible luck needed.

For the finish, I remember a radio spot here that is used to show how good radio commercials can be: the marsrover is calling home, telling us, that he is bored with red stones eeeevery day and more red stones and even more and please pick me up home. But wait, someone is approaching.... silence.

So let these guys pickup or destroy an earth bound probe and let the other side going for that "evidence" they just collected - that would be perfect, because half of all space agencies on earth would try to reestablish communication with that lost probe and are looking with their finest equipment in the right direction at the right moment.


EDiT: Well, if you want the most greatest audience possible, place your point of storytelling some time in future, let the whole world (or at least these who own a TV or a PC) witness the brave mars explorer crew placing their first foot at Mars. Just in the moment the mission commander places himself and his crew in front of a UN-Flag to make a selfie-stick supported group selfie, a unknown ship approaches and takes these guys in custody to find out what part they do play in their interstellar war - on livestream.


This is quite simple

The speed of light is 299792458 meters a second or 186282 miles a second. For example it takes the light 9 minutes to travel from the sun to Earth. Even if I have a super powerful telescope, I still need to wait for the speed of light to send the signals. So depending on how quickly you want the battle to be seen from earth your distance follows this. For example if the space fight occurs around Alpha centauri A it will only be detectable from earth 4.3 years after it happens and this assumes their lasers are extremely bright, if the lasers are as bright as lightbulbs or lazer pointers, it is unlikely we will ever see it.

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    $\begingroup$ thats only if a laser is pointed directly at the earth, and if its strong enough to travel that far. Would I be able to observe a 10kt nuke going off at Alpha Centauri? would I be likely to? $\endgroup$ – Marky Jun 10 '16 at 18:03
  • $\begingroup$ Alpha Centauri, or any star, is putting out many orders of magnitude more energy than 10kt, so no. $\endgroup$ – Seeds Jun 10 '16 at 18:05
  • $\begingroup$ @Marky if my math serves me right, eventually yes, but it would be soo dim compared to Alpha centauri A, you would need to already know where it is to be able to notice it $\endgroup$ – TrEs-2b Jun 10 '16 at 18:06
  • $\begingroup$ @TrEs-2b I think you're right. From Orders of magnitude (power), Tsar Bomba, the largest nuke ever built, weighs in at 33.8YW, while the output of our sun is 384.6YW $\endgroup$ – Cort Ammon Jun 11 '16 at 0:23

Let me quantify the notice part, given (in other answers) that ordinary and common instruments can detect your postulated actions.

With programs like LSST, it will be noticed within a week if it's on the night side of the planet.

With terrestrial instruments, any action going on out there on the far side of the sun (that is, visible in the daytine sky) will be washed out by the sky so it will take a few months before the event is visible against the night sky.


We have a number of radio telescopes that scan the sky so if the fleets are emitting radio signals there is a good chance those will be picked up.

If they are using nuclear weapons widely the flashes will probably be picked up too.

The distance does not make that much difference, it won't be a problem to pick those up from the edge of the solar system.

Radio waves are probably the better option though. New Horizons for example is communicating with Earth through the DSN on regular bases, so if loud radio wave sources appear in the vicinity of Pluto it will detected fairly quickly.

  • $\begingroup$ Would they be detected from behind a planet? Surely distance makes SOME difference? As for the flashes, are there not asteroid impacts on planets in our system that "flash" brightly, but we miss? at what point does the probability scale tip from "we could detect that" to "we will detect that?" you seem to be suggesting distances measured in light minutes/hours/days/years beyond the edge of your solar system $\endgroup$ – Marky Jun 10 '16 at 18:15
  • $\begingroup$ @Marky Pluto is tiny, it's under 1500 miles across so it won't be able to hide the battle. The nuclear flashes will be much brighter than any asteroid impact and those are quite rare, while fleets battling it out with nuclear weapons will likely produce hundreds or even thousands of them. $\endgroup$ – ventsyv Jun 10 '16 at 18:23
  • $\begingroup$ Unless the battle concludes very quickly there will be plenty of time for us to detect it and the nuclear flashes and/or radio waves will make it extremely clear what's going on. $\endgroup$ – ventsyv Jun 10 '16 at 18:47
  • $\begingroup$ Um, you might want to read up on the Inverse-square law, distance makes a huge difference, some might say all the difference. $\endgroup$ – Seeds Jun 10 '16 at 21:14
  • $\begingroup$ For a signal around a gigawat at 1 mile distance, a rough calculation tells me the signal would be about 6 picowatts at earth. $\endgroup$ – Seeds Jun 10 '16 at 22:04

Something the size of a [small] planet is only just barely visible at the range of Pluto, so unless they have REALLY big ships, they probably won't be visibly. Nukes are just a brief, bright, flash, unless you know what you're looking for, you may see it and discount it as a closer in meteoroid or some such.

Now, if someone was using a radio telescope in that direction, they might detect enough interesting EM noise to suggest that optical telescopes focus out there, after figuring out where the signals are coming from.

Still you aren't going to see much except flashes.

Now if there were in as close as Mars, that'd be a different story.

  • $\begingroup$ So you are saying "maybe-kinda-but-sorta-no" for a battle around Pluto and "probably-maybe-sorta-kinda-yes" for a fight around Mars? $\endgroup$ – Marky Jun 10 '16 at 18:21
  • $\begingroup$ Right, at least for Mars we can see surface features in optical telescopes, and the planet itself is naked eye visible. So things happening on a large enough scale would be noticed and be distinguishable. $\endgroup$ – Seeds Jun 10 '16 at 18:26
  • $\begingroup$ Pluto is barely visible because it's very faint not because it's small. $\endgroup$ – ventsyv Jun 10 '16 at 18:35
  • $\begingroup$ Low albedo. $\endgroup$ – Lumberjack Jun 10 '16 at 18:36
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    $\begingroup$ Pluto is, mostly, barely visible because it's so far away, and only very recently has it been visible as anything other than a smudge. So it's pretty much guaranteed that something as small as a spaceship isn't going to be visible at all. Thus my suggestion that Mars-like distances would be better. $\endgroup$ – Seeds Jun 10 '16 at 20:51

We noticed when the aurora went haywire. The sky was lit from horizon to horizon with brilliant green dancing fire. That first night, the whole world watched in awe of the beauty. As the days went by and the aurora only intensified, I watched as awe was replaced by curiosity, and curiosity replaced by fear.

After two weeks of uninterrupted aurora, we found it. Or should I say we found "Them."

Normally aurora is caused by charged particles from the sun, but evidently solar flares aren't the only way to create a massive stream of charged particles....

  • $\begingroup$ I like the inworld perspective, and the idea of radiation from the fight causing an aurora is fun, but how grounded in reality is this? would a nuke fight out near Neptune case this? Would laser splash from Saturn?It does give people a reason to go looking where they might not have before but a few weeks is kind of a long turn around $\endgroup$ – Marky Jun 10 '16 at 19:28
  • $\begingroup$ @Marky I was thinking more along the lines of a Photon Torpedo or Ion cannon. $\endgroup$ – Lumberjack Jun 10 '16 at 20:02
  • $\begingroup$ @Marky The aurora change could also be caused by their propulsion systems. $\endgroup$ – Lumberjack Jun 10 '16 at 20:06
  • $\begingroup$ I think if they were in orbit of Earth using some kind of charged particle propulsion, it might excite some small localized auroras, the energy to do the whole sky for weeks would probably sterilize the planet. :) $\endgroup$ – Seeds Jun 10 '16 at 21:07
  • $\begingroup$ @Seeds Would it really though? This NASA article seems to imply that the atmosphere and magnetic field are effective protection against positively charged heavy ions from the sun. $\endgroup$ – Lumberjack Jun 10 '16 at 21:15

This is an interesting question that was answered by the hilarious question of, "how many flashlights would it take to show up on the moon".


While this doesn't answer your specific question, it lets you know the sheer magnitude of light needing to be put out to show up as small scale objects.


Yes. And no.

We regularly detect fast moving, large asteroids, and their courses are tracked. So far, observers around the world have found and tracked more than 10,000 near-Earth objects. Most are a about 140m (I don't have a source for this). Rosetta was identified and tracked from near the distance Jupiter is from us, but it's pretty large.

One of our observers would see anomolous moving 'asteroids' and get very curious about it. But we can't even see lunar equipment with any detail. So this would require the time and energy to go near this space war, which likely would be over or moved long before we got there.

So we could see that there's something artificial moving around, but it would be very difficult to find out what was going on. Complicated by trying to get a trajectory if dots of light are moving long distances.


Spotting the fight is going to be somewhere on unlikely end of a scale of probability.

Lasers we won't see unless they miss their target and directly hit a telescope. A good laser only projects energy along the beam, unless it hits something (or you) you never know its there.
Railguns we won't see at all.
Nukes we won't see unless a radio telescope is pointing the right way at the right time, and even then we're on a speed of light delay. Even if we see something it may well not be until everyone has long since cleared the area. One won't be enough to extrapolate information from, we'd need to see a cluster before we started considering that option.

Following the line of thought that says only nukes could be seen we need to work out how far away we could spot them from and how many we'd need to see before we worked out what was going on.

I'm leaning towards it being highly unlikely we'd see the brief speck in the vast darkness that would be a space battle.

  • $\begingroup$ this is my inclination too, but we WOULD notice if if they started playing with each other in orbit (I hope.) If we noticed there, we would probably notice around the moon to... but what about mars? juputer? out in the interstellar gulf between Sol and Alpha-Centauri? $\endgroup$ – Marky Jun 10 '16 at 19:23
  • $\begingroup$ @Marky maybe sometimes the shooting stars are actually the slugs from railguns burning up in our atmosphere. We'd never know. $\endgroup$ – Separatrix Jun 11 '16 at 20:46

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